The Scientific Harrovian - Issue 2, June 2017

Issue II 2017

Harrovian

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CONTENTS PREFACE INTRODUCTION TO SCIENTIFIC HARROVIAN ISSUE 2017

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MESSAGE FROM THE EDITOR-IN-CHIEF

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SCIENCE IN APPLICATION THE FUTURE OF MANUFACTURING: 3D PRINTING

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BY CHARLES GAI

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ABOUT NERVE AGENTS

BY MRS L SMITH

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CLOSED TRAUMATIC BRAIN INJURY

BY RONALD HSU

APPRECIATION OF SCIENCE THE BEAUTY OF PHYSICS

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BY AMY WOOD

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HOW DOES THE SUN PRODUCE ENERGY

BY JADE HOI LAM WONG

A PERSONAL STORY: THE CONTINUOUS SHIFT BETWEEN MAGIC AND REALITY

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BY TRACY CHEN

EXPERIMENTAL RESEARCH AN INVESTIGATION INTO MANUFACTURING OF BIODEGRADABLE STARCH-BASED PLASTIC 35 FOR LESS DEVELOPED COUNTRIES

BY CHARLES GAI

INVESTIGATING THE STRETCHING OF A SLINKY PRODUCED BY ITS OWN WEIGHT

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BY GREG CHU, DR MICHAEL DANIEL, COURTNEY LAM

AN INVESTIGATION OF THE EFFECT OF NON-ALCOHOLIC DRINKS ON THE GROWTH OF L. CASEI SHIROTA FROM YAKULT IN NON PH-REGULATED SIMULATED GASTRIC

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CONDITIONS IN VITRO

BY RYAN THANG

THE BIGGEST OVERHANG WITH N ONE-METRE RULERS

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BY DR MICHAEL DANIEL, KATRINA TSE, ZELI (BENJAMIN) WANG

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MEASURING THE VISCOSITY OF GLYCEROL

BY ZELI (BENJAMIN) WANG

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From the Editor-in-Chief The Scientific Harrovian is the School’s science journal that provides a forum for students in the Prep and Upper School to publish scientific articles or reports on scientific work and research. The journal is published annually and an editorial board consisting of four Year 12 students and 3 Year 13 students 1 is responsible for the publication this year.

A Scientific Harrovian article could be the result of a genuine interest a student has on a topic in the Physical and Biological Sciences or it could be the report on research that a student has carried out for a Gold CREST Project, a British Physics Olympiad Experimental Project, or a project carried out as an Extra Curricular Activity in a Science Club.

Writing an article helps a student prepare for life in higher education and beyond. In any scientific based degree students are expected to write several scientific papers and reports over the course of their degree, so learning how to do this well early will give the student the edge. Also, the publication of an article in a Science Journal can be included in a student’s Personal Statement and this will allow the student to talk about his/her research interests in a University/College interview.

Requirements for writing an article for the Scientific Harrovian • • • •

The article must be your own work and not a copyright of an another person The article must be on a scientific topic The article must be factually correct The style of the article should be2: o Formal – avoid colloquial language; o Concise – write precisely and avoid waffling; o Structured – break the article into sections with appropriate headings o Impersonal – avoid writing in the first person; o Referenced – if you make a claim that is not your personal findings, it should be supported by reference.

Articles for publication Articles for publication in the Scientific Harrovian must be submitted to the editorial team as Word documents in normal layout: scientific-harrovian@harrowschool.hk Editor-in-Chief Teacher Editors Dr Michael Daniel (Editor-in-Chief) Mrs Lotje Smith

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Student Editorial Board (2016-17) Greg Chu (Y12) (Student Editor-in-Chief) Zeli Wang (Y12) Victor Yang (Y12) Ruijia Zhang (Y12) Foster Chen (Y13) Charles Gai (Y13) (Student Editor-in-Chief) Ronald Hsu (Y13)

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Graphic Designers Ruijia Zhang (Y12) Charles Gai (Y13)

Message from the Editor-in-Chief Dear Readers, It is a pleasure to welcome you back to the second edition of the Scientific Harrovian.

The School’s Science Journal came into existence last year, with the publication of articles written by students in Year 13, and it is encouraging to see that this year we have, also, contributions from students lower down the Senior School.

In every school that I taught in the UK (King’s School (Canterbury), Saint Paul’s Girls’ School (London), and King Edward’s School (Birmingham)) I always wanted to start a science journal to allow students to publish articles in topics of science about which they felt passionate. I had to come to Hong Kong for this dream to materialise. Last year, encouraged by the excellent articles appearing in the Harrovian, I went for it. I appointed myself Editorin-Chief, told the Head Master about the idea and he accepted it – he said ‘that is fine, go ahead’ – and with the Head of Science providing money for the publication, the Scientific Harrovian Issue 1, MMXVI came into existence.

Enjoy reading the articles in the second edition of the journal.

I take this opportunity to thank the Editors for all their hard work and valuable time in in editing the various articles that were submitted for publication. They have done an excellent job. Next academic year Mrs Lotje Smith takes over as Editor-in-Chief.

Yours faithfully, Dr Michael Daniel Teacher of Physics

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SECTION I

SCIENCE IN APPLICATION

The Future of Manufacturing – 3D Printing Charles Gai1 Harrow International School Hong Kong Printing has long been developed throughout the history. The earliest known form of printing, woodblock printing, was developed in China even before 220 A.D [1]. From there, human slowly developed our techniques of printing to the modern standard with a variety of methods such as inkjet printing, thermal printing and laser printing. 3D printing, also known as additive manufacturing, is a new and fast booming technique of manufacturing. With accurate computer coding and control, the desired object is created through successive layering of materials. In some’s opinion, the development of 3D printing marks the beginning of a third industrial revolution [2], replacing the traditional production line with 3D printing machines that are fast yet flexible in prototyping and manufacturing. Currently, 3D printing technology has already been implemented in multiple fields including medicine, clothing and may be soon used to a build moon base in the near future [3]. Between the various types of 3D printing, Fused Deposition Modelling (FDM) is the one most widely used outside industrial scale production. This article will summarize and explain the basic principle behind FDM 3D printing and current challenges that is waiting to be solved as well as the various specific applications of 3D printing in general.

I.

INTRODUCTION

1. Designing and Modeling Stage 3D printing normally begins with the computer-aided design (CAD) software. It can also be done through 3D scanner or photogrammetry software [8]. CAD design has a higher accuracy than other methods as well as ensuring the possibility to alter the design whenever required.

At Harrow, our CAD-CAM club utilities AutoCAD as the main source of CAD software with the support of Rhinoceros software for transferring the file from .dmg (Disk image) or .dxf (Drawing Exchange File) into printable format of .stl (stereolithography).

After designing the object, the model in .stl format will be transferred and processed by another software, usually known as the ‘slicer’. Here, the model is converted into coding that the printer can follow and thus construct the object. This G-Code file contains information about the surface temperature of the platform, number of extruder and its corresponding temperature, idling speed and printing speed. Most importantly, the G-Code file slices the model into series of layers and calculates the movement of the extruder in all X, Y and Z axis. The G-Code can then be ran by the 3D printing client software that is specific to each type of printer.

Fig.1 Harrow CAD-CAM Club Student Designs Fig.2 3D printer (Type FlashForge) 4

2. Printing Stage The printer is automatically set to print a base platform for the object in order to prevent the object from tipping or moving during printing process as well as damaging when being removed from the original platform. To construct overhanging parts, supporting materials are being calculated and printed during the process. However, it is not recommended to print overhanging parts with sharp angle greater than 60 degrees with FDM printers because the time taken will be significantly prolonged and the chance of error calculation will also substantially increase.

Fig.3 Printing the prototype of Harrow school logo The time taken for the printing process greatly depends on three factors, the design of the print, the setting on the extruder and the material choice. Firstly, the complexity and size of the object determine the amount of material usage as well as the time duration. Ironically, 3D printer generally prints complex object with many hollow spaces faster than a solid block.

This can be explained by the layering process as complex object requires less material in each layer. Secondly, the setting on the extruder plays a major role. A higher idling speed and printing speed can result in a shorter period production but may cause deviation in layers and a lower accuracy in general. Production with multiple extruders to create variety in colour and texture can also extensively increase the time duration. Moreover, a setting with a thinner layer (More slicing of layers) can greatly improve the accuracy in the model but the time taken will increase exponentially in return. Lastly, the material choice can affect not only the appearance of the object but also the production time. The main two sources of material in the market are PLA (Poly-lactic acid) and ABS (Acrylonitrile butadiene styrene). PLA, a type of biodegradable plastic, has a lower extruding temperature and a higher density than ABS. Thus, objects made from PLA generally require less time but are less resistive to heating and impact.

Fig.4 PLA chemical formula [10]

Fig.5 ABS chemical formula with three different monomers [11]

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3. Polishing and Finishing Stage After printing, the object should be allowed to cool for 5 minutes before taking off the platform. For ABS-made objects, the surface can be polished and bleached with chemical vapour process [9] such as acetone. On the other hand, abrasive paper (sand paper) can be used for PLA-made objects.

Fig.6 Example of printout (CAD-CAM Student Design)

II.

CHALLENGES

There are still few challenges and issues remain unsolved in FDM 3D printing field.

Although some problems can be better tackled with alternative printing methods such as photo-polymerisation, however, the cost is generally higher than FDM printing. The following are just the two most urgent problems waiting to be solved.

1. Time duration As mentioned in the previous paragraph ‘Printing Stage’, there are multiple factors that affect the production time. If any of the aforementioned factors can be overcome, 3D printing can replace or combine with traditional production line with a lower cost and less requirement of space.

2. Legislations Patent and copyrights of the original designed model remain to be unsolved problems. If a design is patented, any replication, usage and selling is seen as an infringement to the designer. However, anyone who can access the Internet can easily model and produce the same design as long as they have found relative pictures and information about the product. It is hard to distinguish and justify copyrights in such scenarios.

Another alarming aspect of 3D printing is related with gun legislation. It is impossible to prohibit the online distribution of 3D printable weapon files. Although the quality produced by 3D printing are not yet to the standard of those industrialised production, it can be a potential threat to national security as technology keeps on innovating. Some US legislators purpose an implementation of security sensor on each 3D printer to prevent such production whereas some believe the ultimate solution is to regulate the trade on gunpowder [14]. Up to date, the related legislation is still waiting to be decided.

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III.

APPLICATIONS

Over the last three decades, 3D printing in general has already been implemented in multiple fields for different purposes. The fields listed below are just few examples of its application.

1. Structural Engineering MX3D, a start-up design company, is planning to build a bridge in Amsterdam using 3D printing technology in 2017 [5]. Their machine, printing lines with molten metal wire with temperature up to 1,500 !, will construct the bridge from both side and move along with the bridge while building it.

Fig.7 MX3D’s proposal on the construction [5] In addition, a Chinese company had printed a five-stories building using 3D printing technology in 2015. It is estimated that it saved 30%-60% materials and reduced 50%-70% working time, which overall saved at least 50% construction cost [12].

2. Scientific Research 3D printing technology has assisted scientists to explore and carry out experiments with specific geometric-shape apparatus requirement, even in microscopic scale. Researchers from University of Texas had conducted investigation on bacteria communication on a cell-to-cell level in 2013 [7]. They utilized a microscopic three-dimensional (3D) printing strategy to manipulate the 3D geometry of populated bacteria colonies into adjacent, free-floating or nested colonies.

3. Prototype manufacturing Companies had long been exploring the possibility of producing prototype with 3D printing since the birth of this technology back in 1984. For instance, Boeing tests and designs their airplane parts with 3D printed (additive manufactured) prototype. Moreover, a group of students in University of Michigan used an inkjet-based 3D printer to produce a prototype of their self-designed solar-powered car, Infinium [6].

Fig.8 Solar-powered car Infinium [6]

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4. Medical usage The major contribution of 3D printing in the medical field is personalized implants. Implants such as skull and human ear structure have already successfully been replicated and implanted into patients with severe injuries. With this technology, difficult surgeries such as total joint replacement have significant breakthrough in both method and success rate [13].

Furthermore, 3D printing can create tablets with greater surface area to volume ratio, which speeds up the absorption process of the tablet inside the digestive system [15].

Fig.9 3D printed human ear structure implant [16] 5. Clothing The clothing industry is currently investigating heavily on the future of personalized 3D printed customs. In the past, 3D printing has already being used in production of extraordinary outwears such as superheroes’ customs. Indeed, some parts of Iron Man’s suits used in the movie ‘Iron Man 2’ are 3D printed [17]. Sporting goods giants such as Nike and Adidas have also been heavily involved in 3D printed footwear. The Nike Vapor Laser Talon Football cleat, released in 2013, was the first 3D-printed plate to be used in sports industry [18]. Adidias’ Futurecraft series, on the other hand, is working on to establish and mass produce 3D printed running shoe as soon as 2018, which is designed and personalized to every customer [19].

IV.

CONCLUSION

3D printing, as a booming technology and market in the 21st century, has successfully integrated into multiple aspects of the society. The development in printing material associated with 3D printing, varying from 500 nanometer wide filaments for surgical usage [4] to concrete for structural construction, extends its application even further. FDM printing, the most recognisable form of 3D printing, is now available to everyone. With the online distribution of 3D printable files, anyone can design, alter and replicate any desired items they wish to manufacture. Therefore, it is the government’s responsibility to establish related legislations to both protect designer’s copyright and citizen’s safety as soon as possible.

3D printing is already changing the way companies produce their prototype, engineers verify and construct the building and doctors design surgery plans. Although there are still limitations associated with it, 3D printing is likely to bring more changes in how we regard manufacture and construction in the near future with its ever-expanding area of applications.

The cost and complexity of manufacturing is reducing to its minimum with 3D printing.

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Reference 1

Year 13 Student (Sun)

1. Shelagh Vainker in Anne Farrer (ed), "Caves of the Thousand Buddhas", 1990, British Museum publications, ISBN 0-7141-1447-2 2. Jeremy Rifkin, “The Third Industrial Revolution” 2011 3. Ehrenberg, Rachel. “THE 3-D PRINTING REVOLUTION: Dreams Made Real, One Layer at a Time.” Science News, vol. 183, no. 5, 2013, pp. 20–25., www.jstor.org/stable/23598830.

4. Alexandra Goho. “Miniaturized 3-D Printing.” Science News, vol. 165, no. 13, 2004, pp.

196–196., www.jstor.org/stable/4014762.

5. TG. “3-D Printing: BRIDGE TO THE FUTURE.” ASEE Prism, vol. 25, no. 1, 2015, pp.

16–16., www.jstor.org/stable/43531180.

6. TG. “3-D PRINTING: Desktop Manufacturing.” ASEE Prism, vol. 19, no. 3, 2009, pp. 18– 18., www.jstor.org/stable/24163158.

7. Connell, Jodi L., et al. “3D Printing of Microscopic Bacterial Communities.” Proceedings of the National Academy of Sciences of the United States of America, vol. 110, no. 46, 2013, pp. 18380–18385., www.jstor.org/stable/23757552.

8. https://en.wikipedia.org/wiki/3D_printing#cite_note-Jacobs-24 9. Kraft, Caleb. "Smoothing Out Your 3D Prints With Acetone Vapor". Make. Make.

Retrieved 2016-01-05.

10. https://en.wikipedia.org/wiki/Polylactic_acid 11. https://en.wikipedia.org/wiki/Acrylonitrile_butadiene_styrene 12. http://news.mydrivers.com/1/375/375515.htm 13. pubmeddev (2009). "Page not found - PubMed - NCBI". J Oral Maxillofac Surg. 67 (10): 2115–22. doi:10.1016/j.joms.2009.02.007.

14. "Sen. Leland Yee Proposes Regulating Guns From 3-D Printers". CBS Sacramento.

2013-05-08. Retrieved 2013-10-30.

15. http://www.recoveryrestart.com/3d-printed-pill-approved-use-fda/ 16. http://www.smithsonianmag.com/innovation/7-medical-advances-to-watch-in-2014180948286/ 17. https://www.fastcompany.com/1640497/iron-man-2s-secret-sauce-3-d-printing 18. https://www.fastcodesign.com/1672004/nike-vapor-laser-talon-football-s-first-3-dprinted-shoes 19. http://money.cnn.com/2017/04/07/technology/adidas-3d-printed-shoe/

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About Nerve Agents Mrs L Smith1 Harrow International School Hong Kong

INTRODUCTION Substances originally designed to effectively control insect populations in agricultural areas in Europe soon found a dark, almost unthinkably inhuman application in war zones. In this article the author will look at three examples of nerve agents; these are Tabun, VX and Sarin.

The article will cover, and try to answer, the usual questions that spring to mind when curiosity and interest are stimulated. Surprisingly, nerve agents are not particularly complex molecules and hence, A level chemists will find several compounds which form part of the production of these agents familiar. The article further explores the current issues around the application of these deadly substances and the strategies in place to prevent or mitigate tragedies when the nerve agents become available to terrorists.

1. How do these molecules look like?

Fig 1: Tabun

Fig 2: VX

Fig 3: Sarin

2. What is a nerve agent?

According to Geoghegan, J. and Tong, J.L (2006), a nerve agent is a compound that consists of an ester and an amide derivate made from phosphonic acid. Its morphology emulates molecules of organophosphate insecticides.

Fig 4: Phosphonic acid

3. What are their properties?

Nerve agents are mostly liquids at room temperature with high boiling points, low molecular masses and the ability to dissolve lipids. Sarin is the most volatile and has a similar vapour pressure as that of water. It is absorbed by the skin or by inhalation, followed by the

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penetration of the central nervous system. V agents have a long life in the atmosphere which depends on their volatilities, densities and their reactions to water and light.

Property Molecular mass Density g/cm! at 25 °C Boiling point °C Melting point °C Vapour pres. mm Hg at 25 °C Volatility mg/m! at 25 °C Solubility in water % at 25 °C

Tabun 162.1 1.073 247 -50 0.07 600 10

Sarin 140.1 1.089 147 -56 2.9 17,000 "

VX 267.4 1.008 300 -39 0.0007 10 3 (" at < 9.5 °C)

Fig 5: Table of physical properties of Tabun, Sarin and VX

4. How do these agents work?

The agents mainly suppress the secretion of acetylcholinesterase, an enzyme responsible for the breakdown of a neurotransmitter called acetylcholine.

Fig 6: Acetylcholine

Fig 7: Demonstration of how nerve agents prevent acetylcholine from breaking down

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Sarin is more soluble in water than Tabun and VX; the latter are sparingly soluble. VX, however, is more soluble in cold water but only slightly soluble in warm water. The heart of the chemical nerve agent is situated at the phosphorus atom. The P-X bond is very susceptible to nucleophilic attack; nucleophiles such as water or hydroxyl ions are particularly effective. Nerve agents decompose gradually in neutral solutions but very quickly in alkaline conditions, or with a catalyst or at a higher temperature. This forms nontoxic phosphoric acid, which is the basis of the decontamination process. VX, being less soluble, will remain on the ground unless treated with alkaline solutions with a pH between 7-10.

Fig 8: Sarin hydrolyses easier than do VX

5. Toxicity The signs of being exposed to a nerve agent include constricted pupils, profuse salivation, convulsions, involuntary urination and defecation, and eventual death by asphyxiation as control over respiratory muscles is lost. The muscular symptoms are more prominent when a person is exposed to a higher dose. The victim may suffer convulsions and lose consciousness. At this point, other symptoms might not be visible as they might not have had time to develop.

The toxicity, as well as the symptoms developed, depends on how the nerve agents entered the body. The agents are much more effective if the person inhales the gas than if he absorbed it via the skin. This is due to the complex blood circulation system in the lungs which provides a faster route to vital organs and the respiratory system in general. Death may occur within a couple of minutes if a person is exposed to a high concentration of the nerve agent. (Fig 9) Nerve agents can also be absorbed by the skin by penetrating the layers of the skin gradually.

They have the ability to dissolve lipids but it will take time to reach the blood stream.

Therefore, it might take up to half an hour before the first symptoms appear. The time elapsed will depend on the concentration of the agent and the ability to bond to acetylcholinesterase, thereby inhibiting the enzyme's normal biological activity in the nervous system. The table below compares the lethal dosages for inhalation and absorption by the skin.

LCt50 Inhalation (mg/m!)#(min) LD50 Skin absorption mg (for each individual) Tabun 70 4000 Sarin 35 1700 VX* 15 10 Fig 9: Lethal dosages (*LCt50 value is for the aerosolised form) 12

LD50 expresses the dose at which 50% of the exposed population will die as a result of their injuries; ‘LD’ stands for lethal dose and ‘50’ stands for 50% death rate. A different measure is used for inhalation: the product of concentration (C) and time of exposure (t). For example, inhalation of Sarin vapour with a concentration of 100 mg/m3 for one minute gives the same result as inhalation of 50 mg/m3 for two minutes. The toxicity sequence is the same for the two routes of exposure but the differences are much greater in skin exposure. This is mainly caused by the more volatile nerve agents evaporating from naked skin. If the evaporation is prevented, e.g., by tightly fitting clothing, the difference will be less. [Ivarsson et. al. (1992)]

6. Original Application The agents were developed as insecticides and were used for this purpose. According to the Centres for Disease Control and Prevention (CDC) (2013), Tabun was first manufactured by Dr Gerhard Schrader as insecticide in 1936 in Germany. Laura Geggel, a senior writer at ‘Live Science’, claims that Sarin was developed in 1938 in Germany, also by Schrader, and again to be used as an insecticide. VX was developed in the UK in the early 1950s, as stated by the CDC, and its only application was that of chemical warfare.

Fig 10: Dr Gerhard Schrader

7. How are these molecules manufactured?

Fig 11: Manufacturing of Tabun

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Quite a few of the molecules in this preparation forms part of the A2 syllabus and it thus does not require phenomenal chemistry knowledge to be able to produce Tabun. You will recognize the following: 1 and 2 are an amine group and POCl3 (produced from PCl5 and an OH group) respectively; compound 4 is a known salt; compound 9, which is particularly poisonous, is normally used in the nucleophilic addition mechanism with KCN; chlorobenzene, used in the final step, is made from a Friedel-Crafts reaction of benzene using chlorine gas and a catalyst (halogen carrier) such as AlCl3.

Fig 12: Manufacturing of Sarin The preparation of Sarin starts with an alcohol and produces two optically active isomers (enantiomers), covered in the A level syllabus. This reaction is short and synthesis does not require many steps. HF is used as feedstock for the preparation of the polymer Teflon and is a source for fluorine gas. Hydrogen fluoride is a highly dangerous gas, forming corrosive and penetrating hydrofluoric acid (one of the superacids) upon contact with moisture. The gas can also cause blindness by rapid destruction of the corneas.

Fig 13: Manufacturing of VX VX preparation involves a slightly more technical and skilled approach and only a few molecules are known at secondary school Chemistry. It involves more steps during synthesis and produces a racemic mixture of two enantiomers (1:1 ratio) by transesterification. Known molecules for A2 students are the starting molecule PCl3 and reactant with the phosphonate, S8 .

8. (i) When good inventions turn evil Biological and chemical terrorist attacks have occurred since the First World War. The fact that some invisible, unbeatable and mostly undetectable weapon can suddenly attack and cause a painful and certain death was an unbearable thought for soldiers as well as the public. The three

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nerve agents discussed in this article were fortunately only developed after the end of the First World War. In the Second World War, the US, Great Britain and Germany manufactured tonnes of nerve agent stocks but never used it because they were afraid that their adversaries will do the same. After the war, thousands of tonnes of shells and containers with Tabun, Sarin and other chemical weapons were disposed of at sea by the Allies.

The Soviet Union also had the facilities to produce chemical weapons but their development was kept secret.

During the Iran-Iraq War in the 1980s and the 1991 rebellion in Iraq, the government under the leadership of Saddam Hussein used chemical agents, including Sarin and VX, against Iran forces and Iraqi rebels. An example is the Halabja chemical attack.

Sullivan, J. B. (2000) recorded that in 1995, a religious sect, Armageddon, launched an attack on a Japanese subway station using Sarin gas. This killed 12 people and 5500 people were hospitalized.

In 2013, the Syrian government allegedly used Sarin in the suburbs of Damascus, killing more than 1,000 people, according to The New York Times. Syria also used Sarin in an attack on 4 April 2017, killing at least 86 people, including 28 children, according to the Turkish Ministry of Health.

(ii) Why are they such effective war weapons?

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They are not expensive to make

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They are not easily detected

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They are easily spread and transported

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They do not give warning to your senses such as colour or smell

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People who have been exposed do not immediately know that the symptoms were caused by a nerve agent

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They are mysterious and not well known (iii) How can humans, affected by nerve agents, be treated?

Nerve agents have a very quick effect and should be treated immediately. Some armed forces use an autoinjector containing antidotes to nerve agents. It is fairly easy to use; a person can inject herself or another person just by pressing a button. In most cases, nerve agent poisoning could be easily treated with oximes. VX and Sarin are the easiest to treat with oximes, while Obidoxime is the most effective against Tabun poisoning.

If an individual does not improve within a few minutes after the first auto-injection, an additional auto-injection can be administered. The individual should then be treated by qualified medical staff who will inject additional atropine and an anti-convulsant drug, diazepam.

If an individual was exposed to high dosage or over a longer period, a large dose of atropine may be required. The functional level of acetylcholinesterase will gradually be restored by the individual’s own production but this process requires at least two weeks. During this period, and probably in the future, the individual may require medical care for mental disorders such as insomnia, amnesia, difficulties in concentrating, anxiety, and muscular weakness. Mental problems are more frequently diagnosed in cases of exposure to lower concentrations over long periods of time.

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(iv) What strategies to prevent chemical warfare are in place?

In 1925, the Geneva Protocol was signed as an attempt to stop the use of chemical weapons.

It was the Protocol for the Prohibition of the Use in War of Asphyxiating, Poisonous or other Gases, and of Bacteriological Methods of Warfare. Unfortunately, looking at paragraph 8 (i) above, this treaty was not upheld and thus not very successful.

CONCLUSION AND DISCUSSION Fritz Haber, a Nobel Laureate who invented the industrial production of ammonia and hence the production of ammonium-based fertilizers, was also called ‘the father of chemical warfare’. His work during World War I involved the development of chlorine-based chemical weapons such as mustard gas. This was very effectively used at the Second Battle of Ypres.

Chemistry is a phenomenal branch of science: a Pandora’s box, but also a pot of gold at the end of the rainbow; it’s a mixture of good and evil. The good originates from chemistry research designed to improve the lives of millions; the evil is motivated by the desperation of nations or terrorists to win a battle. Good and evil is captured in the application of chemistry.

As a chemist, you will have the responsibility to apply your discoveries to the benefit of mankind. Your journey to discovery will be exciting and exhilarating. Did Fritz Haber have a choice in the application of his celebrated successes? You might one day be the one to make the morally correct choice to this regard.

Sir Humprey Davy (1778-1829) said, “Experimental science hardly ever affords us more than approximations to the truth; and whenever many agents are concerned we are in great danger to be mistaken.”

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REFERENCES 1 Teacher of Chemistry and Senior Housemistress (Keller House) 1. Geoghegan J. & Tong, J. L. (2006). Contin educ Anaesth Crit Care Pain. 6 (6): 230-234 2. Sullivan Jr, J.B.(1987), Toxic and Biological Terrorism.

3. Gupta( R.C.( et# al.(2017)( Acute( Tabun( toxicity;( biochemical( and( histochemical( consequences(in(brain(and(skeletal(muscles(of(rat.(Vol(46,(issue(3,(p(329J341( 4. March(27,(2013(CDC(Centers(for(Disease(Control(and(Prevention,(CDC(24/7:(Saving(Lives,( Protecting(People( 5. Ivarsson(U,(Nilsson(H,(Santesson(J,(eds.(1992)(A#FOA#briefing#book#on#chemical#weapons:# threat,#effects,#and#protection.(Umeå,(National(Defence(Research(Establishment.( 6. Lohs, KH: Synthetische Gifte. 3., überarb. u. erg. Aufl., (1967), Deutscher Militärverlag, Berlin (East).

7. Office of Public health Preparedness and Response. Page last reviewed: May 9, 2013.

Page last updated: November 18, 2015.

8. US Department of State. Geneva Protocol (2002). The Office website Management, Bureau of Public Affairs

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Closed TBI- Traumatic Brain Injury Ronald Hsu1 Harrow International School The brain is the most important organ, according to the brain.

Abstract( We usually associate bone fractures and punctured organs with Road Traffic Accidents, which eventually lead to internal haemorrhage and organ failure. In this article we will be discussing Traumatic Brain Injuries, the most common cause of death after trauma. It contributes to the longest hospital stay and cost, and the greatest cause of morbidity[1].

Specifically, we will be focusing on “closed” TBIs, where the cranium is not fractured. Apart from the primary damages done to a brain during the time of impact, the secondary damage after impact, which is prevalent in approximately 40% of patients[2], will also be discussed.

Two life threatening conditions - Diffuse Axonal Injury and Hematoma- will be the focus of this article.

Do you Mind?

Introduction( The brain only contributes 2% of the body mass, but takes up 20% of energy[3]. The complex connections between synapses give our brains an equivalent of 2.5 Petabytes[4], or 2.5 million Gigabytes of memory. Damage to the brain does not necessarily cause mortality, but more often than not cause morbidity. Brain trauma rarely causes immediate death, yet patients aren’t “living” with half of their bodies paralysed after a stroke. That said, when injuries are so severe that a considerable area of tissue structure is permanently damaged, patients rarely survive.

Due to the essential role of the brain, it has several protective mechanisms. First, the brain is protected by the cranium, which acts as an enclosure protecting it from external impact. As the brain develops at an incredible speed in infants, the cranium does not fully form until 24 months after birth[5], so as to provide free space for brain growth (i.e. fontanelle closing).

Between the brain and the cranium is the Meninges, composed of the Dura, Arachnoid, and Pia Matter. The Subarachnoid space, the space between the Pia and Arachnoid Mater, is filled with the Cerebro-Spinal Fluid.

Apart from the Meninges, the CSF can also be found in spaces called Ventricles. Together, the Ventricles, Meninges, and the spinal cord form a separate circulatory system from the rest of the body. In order to sustain the brain, nutrients are transported from the original circulatory system with a highly selective Blood Brain Barrier.

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Under the protection of these mechanisms, the brain works trouble free. However, in the case of TBI, these mechanisms can cause catastrophic injuries to the brain itself.

Impulsiveness damages your brain.

/%.0&%1(2.33-#4(!5+*&6()*7-%1( Instead of arranging in a random mesh of neurones, the cells are oriented in a way that the axons point at the middle of the brain (white matter), while the cell body itself is on the outer layer cortex (grey matter). As synapses have the ability to converge and diverge, the white matter is where simple neurone signals construct consciousness. Due to the uneven distribution of density, forces experienced during rapid movement could shear the brain across a large area, especially on the axons, thus the name Diffuse Axonal Injury.

Imagine you are holding 100 balloons in one hand. The helium gas lifts the mass up, and the tension in the strings is what prevents them from flying away. Now, say you are on an accelerating car with the 100 balloons. In order for the balloons to accelerate with you, the strings must provide even more tension to â&#x20AC;&#x153;pullâ&#x20AC;? them. The larger the acceleration, the larger the tension. At a certain point, the tension would be so strong that the strings would snap.

This is what happens in an RTA. When the head is subjected to sudden movement in a short period of time, the force on the brain is significant. The impulse of deceleration travels from the seat belt to the thorax, then to the spine, and finally the to brain itself. From there, the 19

impulse travels along the brain stem (hand), along the white matter axons (string), to the brain cortex cell bodies (balloons). When the deceleration is too big, the axons “snap” and cause shearing.[6] In reality, the elastic axons do not completely sever themselves. The cytoskeleton is responsible for the cell’s structural support and intercellular transportation, and it is this particular structure that is sheared. This causes loss of structural support of the cells, which eventually contributes to the mechanical damage of the cells.

The secondary damage is in(tension)al.

Secondary(Diffuse(Axonal(Injury( This primary injury is not the main contributor of Diffuse Axonal Injury. Secondary injuries, usually biochemical cascades, occur hours or days after trauma.[7] After the axons are damaged, intracellular transport along the originally-intact cytoskeletons is now disrupted. Axonal transport causes a buildup of materials at the site of damage. As the swelling pressure accumulates, the already damaged axons would no longer be able to support the increasing tension without the help of cytoskeletons. In this instance, the axons themselves break and the long structure retracts to the cell body itself, forming a “retraction ball”.

In common nerve damage, the neurolemma (outer layer of myelin sheath) provides temporary support at the site of injury. Nerve fibres send out “sprouts” under growth factors produced by nearby Schwann cells, which tries regrow reconnect the nerve. However, unlike the Peripheral Nervous System, where the neurons are myelinated by Schwann cells, the Central nervous System is myelinated by oligodendrocytes. Therefore nerve “sprouts” cannot be grown, leaving recovery impossible.

After axon severing, Wallerian degeneration occurs in an anterograde direction (proceeding from the cell body to the axon end). Approximately 24-36 hours after axon severing, both the axolemma (axon membrane) and myelin sheath degenerates, where macrophages later come in to clear up cell debris.[8]

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Meanwhile, when the axolemma gets stretched during trauma, the mechanical force may damage Sodium-pumps, creating pores in the axolemma itself. Due to the uneven distribution of a resting (polarised) neurone, large amounts of Calcium and Sodium ions flow into the cell.

The high level of intracellular Calcium ion damages mitochondria, triggering phospholipases and proteolytic enzymes that break down protein molecules. Spectrin, a protein responsible for anchoring the axolemma to the cytoskeleton, is broken down in the process. This ultimately leads to the breaking down of the axolemma and cytoskeleton.[9] If that does not kill the cell, the high level of Calcium ions would activate Caspase, an enzyme responsible for the signalling of programmed cell death.

I set fire to the (b)rain.

940&$+0&(:/&$;+6+<1=( The brain receives 750ml of blood per minute.[10] With countless branches of arteries and capillaries inside the brain, Hematoma is very common, and very serious.

During impact, the brain experiences contusions (bruises). Not only does the brain itself get damaged, the capillaries themselves are also ruptured. In contusions, the intracerebral haemorrhage is relatively controllable, as the brain tissue itself acts as a barrier to block the bleeding. The bleeding is relatively shallow and the haemorrhage has little mass effect.(see below) Usual treatment would be removing the bruised brain, decreasing mass effect and terminating intracerebral haemorrhage.

However, arteries or veins may also be torn during injury, leading to bleeding and subsequent clotting, called Hematoma. Branching into the different layers of the meninges, different parts of the cerebral arteries can cause bleeding. This sudden increase in blood flow to the the constricted volume of the skull increases the Intracranial Pressure. Compared to Sub-Dural haemorrhage, which is caused by broken veins, Epi-Dural haemorrhage on the other hand is caused by broken arteries, thus much more life threatening. Sub-Arachnoid haemorrhage, meanwhile, may cause complications such as Communicating-Hydrocephalus due its blood clot.

Your brain is no better than your kitchen sink.

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940&$+0&(:91,%+'4>;&6-#=( The brain has an isolated â&#x20AC;&#x153;circulatory systemâ&#x20AC;? called the Cerebrospinal Fluid, which circulates in the four ventricles. The volume and pressure of the CSF is always changing.

Luckily, this is one of the various negative feedback systems in our body, and if the pressure is too high, the reabsorption rate is increased. This allows our brains to function under normal pressure.

However, if the circulatory pathway is blocked, there will be little reabsorption at the Arachnoid Granulations, while continuous production at the start of the Choroid Plexus. This causes and an increase in CSF volume and pressure, causing a compression on the brain itself, known as Hydrocephalus.

Classified into two main types - Obstructive and Communicating- Hydrocephalus causes an increase in ICP, which leads to mass effect on the brain. Obstructive Hydrocephalus is the obstruction of the ducts between the separate ventricles. It is usually the obstruction of the aqueduct between the third and fourth ventricle. Obstructive hydrocephalus can be primary (where the site of obstruction is inside the duct, usually due to blood clot of cell debris) or secondary (where the site of obstruction is outside the duct, usually due to mass effects like tumour or Hematoma).

Communicating Hydrocephalus occurs when there is a malfunctioning in the reabsorption of CSF. The ducts between Ventricles are not blocked, and it is the Arachnoid Granulations (invaginations in the Arachnoid Matter that help direct the CSF into vein cavities called Sinuses) that are blocked due to its fine structure.

Therefore after the Sub-Arachnoid haemorrhage, the blood clots may block the Arachnoid Granulations. As the Choroid Plexus continues secreting CSF, pressure builds up in the ventricles and Communicating Hydrocephalus is formed.

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I am going to ruin your cake-baking career.

Hematoma((Mass(Effect)( All the injuries seem to point towards the same end result: Mass Effect. Mass effect is the effect brought to the brain itself when there is extra mass inside the constricted volume of the cranium. Mass effect can be caused by tumours and Hematoma, or Hydrocephalus, which causes an increase in the ICP. When there is a prolonged pressure on the brain, vital brain functions can be affected. Luckily, the Herniation(see below) of the brain is preceded by differentiate signs. In general, an increase in ICP will lead to headaches, nausea, vomiting (vomiting centre in Medulla Oblongata), muscle spasms (motor cortex), and even loss of consciousness. In the case of infants, the increased ICP can cause an enlargement in the head, a typical sign of Hydrocephalus.

Head enlargement in infants is a “lucky” phenomenon. Compared to adults, whose fontanelle has already been fused and thus having no room for expansion, pressure constantly builds up until Herniation occurs.

Herniation, also called “coning’, is the major cause of death in head injuries. Imagine holding a pastry bag filled with whipped cream. Squeezing the bag with the hand would put pressure on the cream, thus squeezing the contents out of the small opening at the bottom.

The same happens in the brain, except instead of having an external force increasing the pressure of the contents, the mass itself enlarges, building up pressure. At a certain point the brain structure itself cannot withstand the pressure, and is squeezed out of the foramen magnum, an opening at the base of the skull. This puts pressure on the cerebral arteries and the brain stem, terminating vital functions like cardio and respiratory control. The pressure also compresses the Oculomotor nerve, causing characteristic uneven eye pupils known as “coned eyes”.

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Conclusion( Like a Hermit Crab, our brain gains critical protection from the cranium. However, we cannot change the structure confining our brains. When brain size increases due to mass effect like Hematoma, tumours, and Hydrocephalus, pressure on the brain increases. Under slight compression, common symptoms like vomiting can give clues to the underlying complications. When pressure increases, focal signs starts to appear. The site of lesion causes focal neurological deficits corresponding to the brain area responsible for specific functions, giving an approximate idea of where the lesion is.[11] â&#x20AC;&#x153;However, the majority of patients with brain injury do not have a lesion suitable for neurosurgical intervention.â&#x20AC;?[12] Currently, in order to reach the site of lesion, the outer structure has to be mechanically damaged. Body functions localised in the outer cortex can be permanently damaged. Unlike other surgeries, it is virtually impossible to seal ruptured arterioles in the brain, as they are essential to deliver nutrients. Therefore the most common treatment for TBI is Decompressive Craniectomy, where the bone flap is removed and obvious masses (usually Hematoma) cleared. The skin is sutured without replacing the bone flap, and only when the condition gradually improves and the patient becomes hemodynamically stable would the bone be replaced through Cranioplasty.

References 1. MacKenzie EJ, Siegel JH, Shapiro S, Moody M, Smith RT. (1988) Functional recovery and medical costs of trauma: an analysis by type and severity of injury. J Trauma 2. Narayan RK, Michel ME, Ansell B, et al. (May 2002). "Clinical trials in head injury". J. Neurotrauma. 19 (5) 3. Clark, DD; Sokoloff L (1999). Siegel GJ, Agranoff BW, Albers RW, Fisher SK, Uhler MD, eds. Basic Neurochemistry: Molecular, Cellular and Medical Aspects. Philadelphia: Lippincott 4. Reber, Paul (2013). "What Is the Memory Capacity of the Human Brain?". Scientific American 5. Beasley, Melanie. "Age of Closure of Fontanelles / Sutures". The Center for Academic Research and Training in Anthropogeny (CARTA) 6. Wasserman J. and Koenigsberg R.A. (2007). Diffuse axonal injury.

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7. Arundine M, Aarts M, Lau A, Tymianski M. (2004) Vulnerability of central neurons to secondary insults after in vitro mechanical stretch. J Neurosci 8. Cowie R.J. and Stanton G.B. (2005). Axoplasmic transport and neuronal responses to injury. Howard University College of Medicine 9. Castillo M.R. and Babson J.R. (1998). Ca2+-dependent mechanisms of cell injury in cultured cortical neurons. Neuroscience. 86 (4): 1133â&#x20AC;&#x201D;1144 10. Walters, FJM. 1998. "Intracranial Pressure and Cerebral Blood Flow." Archived May 14, 2011, at the Wayback Machine. Physiology. Issue 8, Article 4 11. Franz J. Wippold II (2008). Focal Neurologic Deficit. AJNR November 29 12. Douglas Bowley, Kenneth Boffard (2002). Pattern of injury in motor vehicle accidents.

World Wide Wounds Image Source (respectively) https://upload.wikimedia.org/wikipedia/commons/8/82/DTI-sagittal-fibers.jpg https://upload.wikimedia.org/wikipedia/commons/0/09/Contrecoup.svg https://upload.wikimedia.org/wikipedia/commons/3/34/Gray631.png https://www.slideshare.net/gesmundo/loss-of-consciousness http://www.buzzle.com/images/diagrams/labeled-brain-diagrams/brain-ventricles.jpg http://www.csuchico.edu/~pmccaffrey//syllabi/CMSD%20320/images/U3Meninges.gif https://en.wikipedia.org/wiki/Hydrocephalus#/media/File:Hydrocephalus_with_sunset_eyes.j pg http://files.recipetips.com/kitchen/images/refimages/decorating/pastry_bags/howto_using_hol d_bag_correctly.jpg https://s-media-cacheak0.pinimg.com/originals/0f/51/44/0f5144260ab71d916d84807b5b31bf43.jpg š Year 13 Student (Sun)

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SECTION II

APPRECIATION OF SCIENCE

The Beauty of Physics Amy Wood1 Harrow International School Hong Kong Many people see physics as a difficult, equation-packed subject, however many people may not realise that physics brings beauty into our everyday lives which we take for granted.

Below, I shall explain the physics behind sunsets and why the sky is blue.

Visible(Light( Visible light is part of the electromagnetic spectrum and allows us to see the world around us.

White light is simply light that is made up of all of the colours and comes from the sun.

Visible light is separated into seven different colours according to their wavelengths. The diagram below shows the colours from the longest to the shortest wavelength:

Why(is(the(sky(blue?( The sun emits white light, and during the day, this white light reaches earth and enters through the atmosphere. As it enters, the white light is separated into each individual colour (red, orange, yellow green, blue, indigo, violet). Once each colour has been separated, molecules in the air, such as nitrogen and oxygen, causes each colour to scatter. The amount of light scattered is inversely proportional to the fourth power of the wavelength, therefore the shortest wavelengths are scattered most strongly.

If(the(shortest(wavelengths(are(scattered,(why(isnâ&#x20AC;&#x2122;t(the(sky(violet?( Firstly, the spectrum emission from the sun is not constant of all colours â&#x20AC;&#x201C; there is less violet or indigo light being emitted from the sun than there is red or blue. Secondly, the

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photoreceptors in the retina of the eye that detects colour (cones) are less sensitive to violet or indigo than blue, therefore causing us to see more blue than violet. Finally, whilst the strongest violet and indigo light will stimulate red light, most of the indigo or violet light will stimulate the blue light, creating a pale blue colour during the day.

D;&$('&-#4#(&(#-*#4$F( You may ask: â&#x20AC;&#x153;if blue light gets scattered, why do sunsets make the sky red?â&#x20AC;? Well, this is where physics shows its true colours. During the day, the sun will be directly above us, and this allows the blue light to be scattered everywhere by air molecules, however as the earth rotates, the sun will start to set. In doing so, the light has to travel further across the atmosphere to reach us. This causes the blue, indigo and violet light to be absorbed more easily, as they have to travel further to reach us and have shorter wavelengths. In contrast, the red, orange and yellow wavelengths are much longer in length, and are able to travel further and reach us. This causes the sky to appear pink or orange and the sun to look red, creating a beautiful sky.

Sunset from my house in Collaroy, Sydney

References 1. Year 11 (Keller)

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How does the sun produce energy?

Hoi Lam Wong Jade1 Harrow International School Hong Kong

In science lessons, teachers taught students that all energy originated from the sun. For example, the light energy plants absorb to convert to chemical energy. But how does the sun produce its energy?

The sun is mostly made of protons. Protons are subatomic particle found in every atom.

These protons have a positive charge and will repel each other because like charges repel. At the core of the sun, gravitational attraction produces immense pressure and temperature, which can reach over 15 million degrees Kelvin. Because of this, these protons are in an extremely kinetic state, travelling in rapid velocity. Thus, they are more likely to collide and fuse together instead of repelling off. In this case, the kinetic energy overcomes the force of repulsion.

In the core of the sun, hydrogen fuse to form helium. This is called the fusion process and is the thermal nuclear conversion of hydrogen into helium.

The following diagram is a p-p cycle which explains how does hydrogen become helium. The electrons are not involved as they are stripped away due to high temperature and pressure.

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Step 1: Protons move fast enough to overcome the electrostatic repulsion and they get close enough to allow the nuclear forces to take over.

Step 2: A deuterium nucleus is formed by the conversion of a proton into a neutron.

Step 3: Two helium-3 nuclei fuse to produce helium-4 and two protons.

Thus, we can conclude that the net result is: 4 Protons % Helium-4 nucleus + 2 positrons + 2 neutrinos Below is another version of the pp cycle. This version clearly states that this process is a cycle and never ending. However, this cycle will end when the hydrogen in the core is exhausted.

The core is the only part of the sun that produces the energy through fusion. 99% of the energy produced takes place within 24% of the Sunâ&#x20AC;&#x2122;s radius. The rest of the Sun is heated by the energy that is transferred from the core.

The fusion of protons ultimately leads to the loss of mass, which is converted into energy.

This is proved by Albert Einsteinâ&#x20AC;&#x2122;s famous equation: E = mc2. E stands for energy, m stands for mass, and c stands for speed of light (3 x 108, to be precise).

Even though the loss of mass is extremely small, the speed of light is unbelievably fast, therefore the energy released in every fusion cycle is quite large as well. About 4,000,000,000 kilograms of the sun are lost to energy every second.

Because the pp cycle states that 4 protons produce a helium-4 nucleus, two neutrinos and two positrons, we are able to calculate the mass deficit by obtaining the mass of 4 protons and subtracting the mass of a helium-4 nucleus and the 2 positrons.

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4 Protons → Helium-4 nucleus + 2 positrons + 2 neutrinos ! + ! + ! + ! = !"!! + 2! ! + 2!" !" = 4!!"##!!"!!! − !!"##!!"!!"!! !−!2!!"##!!"!!"#$%&"' !" = (4×1.00728) ! − ! (4.00260) ! − ! (2×0.00055) !" = !4.02921 − 4.0037 !" = !0.02542! ! = !!"#$#%&!!"#$%!!!"##!!"#$!

1.661!×10!!" = !1!! !ℎ!"!#$"!,! !" = ! (0.02542!×1.661)×10!!" !" = 0.0422!×10!!" !" = 4.22!×10!!" !" !" = !"×! ! ! = 3×10! !/! !ℎ!"!#$"!,! !" = (4.22×10!!" )×(3×10! )! !" = !4.22×10!!" ×9×10!" !" = !37.98×10!!" !" = !3.798×10!!"! !

The mass of a proton is 1.00728u, the mass of a helium-4 nucleus is 4.00260u, and lastly a positron has the mass of 0.00055u. By calculating the mass deficit, the mass lost to energy in every fusion can be calculated.

Thus, in the above calculation, it is proved that 4.22 x 10 -29 kg is lost in every fusion. By taking this mass and substituting it into Einstein’s equation, it is possible to calculate the energy released in every fusion. According to the calculations above, 3.798 x 10-12 Joules are released. According to the Universe Today2 website, about 600 million tons of hydrogen are converted into helium every second. The hydrogen basically is the proton. As shown earlier, the mass of 4 protons is 6.695!×10!!" kg and every fusion of 4 protons releases 3.798!× 10!!" Joules of energy. Hence, 600 million tons of hydrogen converted into helium per second releases 3.405!×10!" J/s Small amount of this energy, 1,21×10! J/s per square metre reaches the earth and supply us with life. Without the sun’s release of energy, life on Earth would not exist.

Medawar believes that the answer to the question “How did everything begin?” cannot be empirical in character. Such questions must seek transcendent answers such as the belief in God, that is answers that do not grow out of or need to be validated by empirical experience.

On the other hand, the question about where does the energy come from to allow fusion to take place can be answered. Research shows that this energy came from the loss of gravitational potential energy when the atoms came together to form a protostar that ultimately gave rise to the star we call the Sun, giving energy to all.

Reference 1

Year 11 (Keller) YouTube video https://www.youtube.com/watch?v=Ux33-5k8cjg 2 Google search

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The Continuous Shift Between Magic and Reality Tracy Chen1

Harrow International School Hong Kong

INTRODUCTION Magic has always been something that people, especially children, have an interest in. I still remember that astonishment when I first saw magnets repelling or attracting each other. I thought I saw magic power. Clearly, that was not magic but a scientific phenomenon, called the Magnetic Effect. I only understood this later, and consequently, stop yelling and pointing like a fool at two magnets and rather investigate the world of science behind this phenomenon. After that, whenever I found my young friends astounded by similar “magiclike” phenomenon, I would say to them with pride, “That is nothing related to magic, it is just basic science.”

I do not believe in magic or fantasy anymore, but I kept my fascination with science. I was still interested in the amazing phenomenon around me as well as the reasons behind it. And in fact, the “reasonable” science seemed far more reachable and understandable than the “magic” lying behind fairy tales.

Then, one day, I suddenly realised that it would be impossible to separate “magic” and “science”, or try to limit myself in “the world of science”. In other words, I found that magic itself, to some extent, is science.

DEFINITION OF MAGIC Oxford dictionary (1) defines magic (n.) as: The power of apparently influencing events by using mysterious or supernatural forces.

And the definition of supernatural (adj.) is: attributed to some force beyond scientific understanding or the laws of nature.

From the definitions above, we can infer that magic is something “beyond scientific understanding.” Seemingly, this contradicts my statement that “science is magic”, but if we take a closer look at the phrase “scientific understanding”, it should appear more reasonable.

Science understanding is not complete, and it is always changing. Atoms had been once said to be the smallest inseparable particle; an imaginary substance called phlogiston had thought to be the cause of combustion; geocentric theory had been considered to be the irrefutable fact of science… The fact that these theories are all superseded by more developed theories provides evidence that in science, what might be considered as absolute fact, may still be challenged and altered in the future.

OUR CURRENT SCIENCE WAS MAGIC IN THE PAST Long ago, our ancestors thought that lightning was magic created by God, but now our science has told us that it is caused by a procedure called electrostatic discharge when a cloud is charged and then discharged during a thunderstorm. Therefore, the former “magic” has become science, whilst lightning itself remains unchanged.

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Not only can a “magic event” be explained by science, but we can also use science to fulfill our dream of magic. Flying vehicles, such as the chariot of the sun, which were once thought to exist in fiction only, are now a normal means of transportation (airplanes).

Everything around us can be considered as “magic” but most of us are so used to our surroundings that we simply ignore its magic. Consider mobile phones, aren’t these devices providing the sort of “remote hearing magic” described in the past? And the video chatting online can resemble the “magic mirror” that allow people to see each other at a distance.

WHAT IS NEXT? – AN ONGOING ATTEMPT OF TELEPORATION Teleport (v.) means to transport or be transported across space and distance instantly according to the Oxford dictionary (2) Some creative ideas, such as teleportation, might seem “unrealistic”, “impossible” and even “against science” to some of us now, but there is a possibility for them to actually happen in the future.

In this article, I will use the example of teleportation. Scientists have been investigating it since the twentieth century despite how fictional it may sound.

When talking about the possibility of teleportation, there is an essential physics concept that should be introduced: quantum entanglement. When two particles, e.g. two photons, are in an entangled quantum state, they behave as a single entity, when one of them undergo a change of state (e.g. when the direction of spin alters), the other one will undergo a change corresponding to the change of the former particle, regardless of the distance between these two particles (3). Even when the distance between this pair of entangled particles is long and even when there is no medium of information transportation between them, this phenomenon still happens. In other words, by altering the state of one particle, we can indeed interfere with something elsewhere, even if it is in another solar system. This may sound impossible and violate our classical view of the world, however, it had been verified to be a fact in quantum physics.

The phenomenon of quantum entanglement was mentioned in 1935 by Einstein and his group of researchers (4), but it was Schrödinger who first used the word “entangled” in the same year to describe this physical state (5). As Schrödinger stated: “the entangled particles, can no longer be described in the same way as before, that is to say, by endowing each of them with a representative of its own” and this phenomenon “enforces its entire departure from classical lines of thought.”

In the following decades, the verification and testing of such entanglement had been taking place but since it is difficult to take measurements without disturbing the system, this process was rather slow. Then in 1964, physicist John Stewart Bell, came out with a suggestion of suitable experimental technique (6). This technique allowed quantum entanglement to be verified by other physicists including the team of Alain Aspect in 1982. (7) This newly discovered quantum phenomenon had led to the development of new technology such as the “quantum teleportation”, which was suggested by Charles H. Bennett and his team in 1993 (8). In their published article, “Teleporting an Unknown Quantum State via Dual Classical and Einstein-Podolsky-Rosen Channels”, Charles H. Bennett and his team 32

confirmed the feasibility of such teleportation. Hereafter, many successful experiments have been carried out, (from teleporting photons (9) to atoms (10)) and the process of developing quantum teleporting is still continuing.

Quantum physicists nowadays are focusing on its possible use of tele-communication, in other words, transferring digital data, instead of teleporting organisms or human beings.

Using quantum teleportation to transfer data may sound less interesting than transferring a human being, the importance of it, however, should always be highlighted. On the one hand, teleportation in the IT field is indeed revolutionary and this improvement in communication can change our lives significantly and to a great extent. On the other hand, teleporting large objects or organisms is theoretically possible, though the practical barriers are huge.

Nonetheless, just like stated earlier, as our knowledge expands, the “impossible magical events” can become feasible realities, meaning that even the teleportation of humans can become possible in future.

CONCLUSION—SO WHAT? Long ago, one of my friends who constantly dreamt about the fantasy world, told me that she thinks science is boring, and those who are interested in the scientific reasons behind this world, are “dull nerds who are too serious to have dreams.”

I have lost contact with that friend and don’t know if she still believes in magic or not…..but now I am. As stated before, an interchange between “magic” and “science” can be seen. By gaining deeper understanding of our world, developing science theories and applying them, it is highly possible to achieve the “unbelievable magical effects” that we thought of in our childhood dreams. Teleportation of humans might happen in the future, flying brooms are not impossible and magic wands may not only exist in fairy tales! There is one thing, however, that must be kept in mind - without the use of science, without effort and hard work, such magical events will not happen.

Furthermore, there is another important aspect: imagination and belief. Imagine, if the physicists refuse to think outside the box (5) and if the Wright brothers did not believe that their big machine could fly, neither will the quantum teleportation nor the motorised flight be possible.

Therefore, I believe that we should not forget about the magical world of our childhood or our feeble attempts to explain the unknown. We should believe in them, and through hard work and scientific understanding, turn them into reality.

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Reference: 1 Year 12 Student (Keller) 1) "Magic".

Oxford Dictionaries.

Oxford University Press. https://en.oxforddictionaries.com/definition/magic date retrieved: 04.20.2017 "Supernatural".

Oxford Dictionaries.

Oxford University Press. https://en.oxforddictionaries.com/definition/supernatural date retrieved: 04.20.2017 2) "Teleport".

Oxford Dictionaries.

Oxford University Press. https://en.oxforddictionaries.com/definition/teleport date retrieved: 04.20.2017

URL: URL:

URL:

3) Harry Buhrman, Richard Cleve, Wim Van Dam (2001) “Quantum Entanglement And Communication Complexity”, date retrieved: 05.05.2017 SIAM J. Comput., 30 (2001), pp. 1829-1841 4) Einstein A, Podolsky B, Rosen N; Podolsky; Rosen (1935). "Can Quantum-Mechanical Description of Physical Reality Be Considered Complete?". date retrieved: 04.20.2017 Phys. Rev. 47 (10): 777–780.

5) Schrödinger E (1935). "Discussion of probability relations between separated systems". date retrieved: 04.20.2017 Mathematical Proceedings of the Cambridge Philosophical Society, 31, pp 555-563 6) J. S. Bell (1964) “On The Einstein Podolsky Rosen Paradox” date retrieved: 05.02.2017 Physics Vol. 1, No. 3, pp. 195-200 7) Alain Aspect, Philippe Grangier, and Gdrard Roger (1982) “Experimental Realization of Einstein-Podolsky-Rosen-Bohm Gedankenexperiment: A New Violation of Bell's Inequalities” date retrieved: 05.02.2017 Physical Review Letters Volume 49, Number 2 8) Charles H. Bennett, Gilles Brassard, Claude Crepeau, Richard Jozsa, Asher Peres, William K. Wootters (1993) “Teleporting an Unknown Quantum State via Dual Classical and Einstein-Podolsky-Rosen Channels” date retrieved: 05.02.2017 Physical Review Letters Volume 70, Number 13 9) D. Bouwmeester, J.-W. Pan, K. Mattle, M. Eibl, H. Weinfurter, A. Zeilinger, (1997) “Experimental Quantum Teleportation”, date retrieved: 05.05.2017 Nature 390, 6660, 575-579 10) Riebe, M.; Häffner, H.; Roos, C. F.; Hänsel, W.; Ruth, M.; Benhelm, J.; Lancaster, G. P. T.; Körber, T. W.; Becher, C.; Schmidt-Kaler, F.; James, D. F. V.; Blatt, R. (2004).

"Deterministic Quantum Teleportation with Atoms". date retrieved: 05.05.2017 Nature. 429 (6993): 734–737

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SECTION III

EXPERIMENTAL RESEARCH

An Investigation into Manufacturing Biodegradable Starch-Based Plastic for Less Developed Countries Charles Gai1 Harrow International School of Hong Kong

ABSTRACT Biodegradable plastic is now widely recognized as the next revolutionary product in manufacturing plastics. However, the biodegradable plastics used today such as Polylactide (PLA) are expensive and require chemical treatment in the manufacturing process. A significant amount of research about biodegradable plastic has focused on the extraction and properties of PLA whereas little research has been done on starchbased plastic that requires negligible chemical treatment. This report discusses the possibility of a starch-based bio-plastic that can be formulated and produced in less developed countries. Soluble starch was used as the base and the polymeric matrices.

Glycerol and sorbitol were used as plasticizers. Water and vinegar were each used as solvent and disordering ions. PLA was tested as a comparison. Other variations including soap, bleach, and raw paper were also tested. Other potential developments such as the transformation of cornstarch into soluble starch with no chemical additive were also carried out as an alternative trial. The impact of different additives on biocomposite properties was studied in terms of three different aspects: antiseptics, mechanical properties, and appearance. A new approach to fabricate a biodegradable plastic was designed. All of the raw materials used are cheap and easy to access in less developed countries.

I.

INTRODUCTION

The increasing demand for plastics and its associated waste problem has raised the awareness of bio-plastics and their potential applications. Currently, 10% of plastics are produced from crude oil [2], causing severe pollution issues in oceans and atmosphere.

Plastics debris in the ocean often result in particles that can degrade and release toxic chemicals such as BPA (Bisphenol A), antimony oxide, heavy metal inks, and styrene monomers [7]. The demand for traditional plastics is particularly strong in developing countries due to their cheapness and durability. However, the continued mass production of such plastic from crude oil may further exacerbate the deterioration of the environment. It is critical to develop cheap and degradable plastics to solve the environmental problems mentioned above.

The concept of developing a new biodegradable material as the replacement for prevailing oil based plastics is both appealing and accessible. The majority of possible biopolymers for this replacement are polysaccharides, for example, starch. Among biopolymers, PLA is a potential solution proposed a few decades ago for the industry and it has already used in many applications such as packaging. However, for PLA the related issue of low thermal stability remains unresolved and attempts have been made to address this issue through various techniques such as compounding strategies. The results revealed additional setbacks, such as biodegradability, taking place when the thermal stability was increased [1]. Moreover, the glass transition temperature (Tg) for typical PLA, such as PLLA

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(Poly (L-lactic acid), is usually around 60 °C as a result of slow crystallization. This relatively high Tg limits PLA’s applications but can be reduced to room temperature through the addition of plasticizers such as glycerol [2].

Another issue with PLA is its relatively high cost. Although PLA has a promising high tensile strength and stiffness, it usually cannot be produced under standard conditions. It requires a range of chemical treatments to transform from starch into PLA. Therefore, PLA cannot be produced nor effectively used in less-developed countries such as Congo and other African nations. As an alternative solution, starch-based plastic will be a suitable alternative for production. According to the Mauritius Sugar Industry Research Institute (MSIRI), bioplastic can be derived from sugar cane waste without affecting the sugar production [15]. If starch-based plastic can be produced in various shapes and sizes and it can withstand a certain amount of compression and tensile forces, it will be possible for people to selfproduce daily-required items. This is a very attractive property especially for less developed countries.

Regarding the goal of improving starch-based plastic’s strength without undermining its biodegradability, it is being proposed that cellulose can be physically blended into the plastic. The hypothesis is tested and reported about the possibility of processing proteins by thermoplastic techniques [1]. The report covers a range of techniques but in general, water and glycerol act as the plasticizer under various temperature conditions. However, very little data has been collected regarding combining current materials with proteins and cellulose. It is hoped that the ability of cellulose to withstand high tension and compression can be successfully combined with plastic without interfering with other beneficial properties such as its lightness in weight and flexibility.

Another aim of the biodegradable starch – based plastic is to limit the spread of disease. According to the World Health Organization (WHO), approximately one and a half billion years of healthy lives are lost annually due to preventable infectious diseases [10].

Many infectious diseases are transmitted as a result of poor hygiene and unclean water supply. Hypothetically, those issues can be overcome and controlled by altering the materials that inhibits bacterial growth. With additives such as bleach and soap, it is hoped that the starch-based plastic can restrain the outbreak of diseases and can potentially be used in local hospitals and health care infrastructure.

My research focused primarily on the production of a biodegradable plastic that is cheap, durable and tough as well as having the antimicrobial effect that can be produced under standard condition in places with the abundant supply of starch and glycerol. The materials chosen for this experiment are all relatively easy to obtain in ample volume. The plastic is aimed to widely implement in replacement of the crude oil-based plastic.

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II.

EXPERIMENTS 1. Materials and reagents

Soluble starch and cornstarch were purchased from the company SciChem. Glycerol, vinegar, bleach, and sorbitol were provided from the school through a local supermarket. The Water used was straight tap water. Walch soap was purchased from a local supermarket. Due to the difficulty of acquiring any primary source of cellulose from local sources or the school, cellulose was filtered and extracted from paper towels and newspaper. All materials were kept in a dry environment for 24 hours before the experiment.

A

B

FIG.1. A) General equipment usage and the products of first two trials B) Oven used to stimulate the temperature near equator

2. Preparation of the blends Starch, glycerol, and water were prepared at room temperature. The blends were obtained by physical blending at room temperature along with heating with a hot pan at a temperature of around 100!C. Glycerol acts as a plasticizer and the volume must be well controlled. The percentage of glycerol will significantly influence the stability of extrudates over long-term storage [3]. After several trials, it was determined that the ratio of blends will be kept the same while mixing in additives. The general recipe for the experiment is water 100cm3, glycerol 10cm3, vinegar 5cm3 and soluble starch 20g. Glycerol will act as plasticizers and vinegar add movable ions to the solution, which increases the rate of the process of disordering the polymer molecules [8].

3. General Processing Method and addition of alternatives 1, Materials’ required: • 1x hot pan • 1x pot • 1x 100ml measuring cylinder

• • •

1x glass rod 1x meter ruler 1x top pan balance

The blends are mixed and heated in a pot on a hot surface under standard conditions.

The temperature is set to 350!C to minimize the time taken. Stirring is required throughout the process. When the water reaches 100!C, fizzing and bubbling will take place. The solution will begin to turn sticky and colour changes from white to brown. After reaching a state where a drop of the solution will not fall from a glass rod within 5 seconds, the solution is transported into a suitable mould where the solution cools down into the shape of the mould. The sample is then left for drying in either the oven under a controlled temperature or outside at room temperature. The changes are obrved daily. Constant flipping around of the sample for faster drying may be required as well. Tests are carried out after the sample is fully solidified.

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4. Experimental techniques The entire experiment is carried out in a fume cupboard and all the blends are aimed to be kept around 5mm in thickness and 5cm in diameter. The hot pan is cleaned and preheated to 40°C one hour before the experiment begins to ensure there is no systemic error with the hot pan and the thermometer. During the experiment, the starch is measured with a top pan balance and cellulose and glycerol are added according to the predetermined ratio.

5. Preparation and extraction of cellulose Methodology and process 1, Additional materials required: • Newspaper or paper towel 50g • 1x blender

•

4x 200cm3 beaker

Paper towel is first cut into smaller pieces and then being dissolved in boiled water in a ratio of 1:20 respectively. The mixture is left to settle and soften the paper for one day and then thoroughly mixed by the usage of a blender for 3 minutes. The resulting solution is left to settle for two days and is treated as an additive of cellulose. Alternative methods used by other researchers [9] suggests a better pure solution can be obtained through re-boiling and treating the solution with 5% (w/v) reagent grade sodium hydroxide, NaOH, followed with 2% (v/v) of reagent grade sodium hypochlorite, NaClO. The solution was then filtered and washed with distilled water until a neutral pH was achieved. However, such method may not be suitable for the production in developing countries where chemical items such as NaOH may be hard to obtain and are potentially hazardous (e.g. NaClO). Therefore, most of the experiment is carried out as the previously described method in part 3. General Processing Method.

6. Addition of Bleach Bleach has been tested as a source of antimicrobial and as a countermeasure to the brown appearance of the newspaper additive sample. The 30cm3 bleach was added to the general ratio of the blend for this trial. The same process method as stated in part 3. General Processing Method was carried out. Four alternative trials were carried out to eliminate the colour of the newspaper solution. Each sample had 5g of small pieces of newspaper added to them. Sample 1 was added with 20cm3 acetone (1mol/dm3). Sample 2 was mixed with 10cm3 ethanol and 10cm3 HCl (2 mol/dm3). Sample 3 was mixed between 50cm3 of newspaper paper pulp and 75cm3 HCl (2 mol/dm3). Sample 4 was mixed with 10cm3 bleach and 10cm3 HCl (2 mol/dm3).

7. Transforming Corn Starch into Soluble Starch A trial was carried out to transform cornstarch into soluble starch with an excess of vinegar (150cm3), a purposed replacement of HCL, with 10g of cornstarch as suggested in previous studies [17]. The trial was stirred periodically over a month and was kept under standard conditions inside the laboratory.

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III.

CHARACTERIZATION METHOD 1. Morphology

Scanning Electron Microscopy (SEM) Microscopic level analysis was carried out with parts of samples that were smooth and clear. Samples were coated with a gold/ palladium alloy and underwent scanning. The scanning electron microscope, Quanta TM 250 FEG, at a voltage of 15.00 kV was used to analyze and support the results of mechanical properties from the Young Modulus tests.

2. Mechanical Properties Tensile Testing Machine After the SEM scans, different parts of the four samples were processed and molded for Young Modulus testing under the standard conditions at 26°C and 75% humidity. RGM4100 was used to determine the Young Modulus of each sample and record the breaking stress. Calculation of the percentage of elongation at break and resistance to load were carried out.

3. Biodegradability Agar Dish Tests The antimicrobial and antiseptic effect of the additives was tested using three different samples with different additives (Newspaper and Soap) and one with no additives acted as a control. The bleach sample was not tested as it cannot successfully solidify. All three 10g samples were cut into 10 equal pieces and sealed in three different fresh agar dishes. Bacteria are added by using a cotton bud scratching the table ten times and ten times on the petri dish before adding the samples. The dishes were kept in the oven with a set temperature of 47°C. The observations were made after an initial 3-day interval and thereafter compared throughout one week.

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IV.

RESULTS AND DISCUSSION 1. Requirements for equipment, temperature and time

The effect of different additives on Tf, Tg and Tm of the starch-based plastic are summarized in Table 1. The formation temperature for all of the trials except trial 5 is 100!C, which is exactly the boiling point of water. The stability in Tf, Tg and Tm suggest a consistent based solution for the experiment and the size of crystallite is similar over the trials. Water acts as a solvent for the experiment and disrupts the pattern of starch molecules while heating. The cross-linking between the molecules takes place during this process. When dried, the disordered polymer chains entangle with each other and form a neat film [8]. This film becomes the base of every starch-plastic throughout the experiment. The time required for the formation of the film increases as additives are added. From the data, it can be deduced that Walch Soap had little effect on disturbing the formation of the plastic, as there is only a 3-minute increment.

Table 1. Thermal properties of different trials

1.Original trial Tf (!C) Tg (!C) Tm (!C) Time taken average (mins) Appearance

100 71 98 15

2.Added Walch Soap 100 71 97 18

Colourless Colourless

3.Added Paper towel

4.Added 5.Added Newspaper Bleach

100 74 97 23

100 72 98 24

N/A N/A 88 31

6.Forming corn starch to soluble starch 100 70 97 19

White

Brown

Brown

Colourless

However, adding paper to the solution resulted in an 8 to 9 minutes increment in time period. The presence of cellulose slows the rate of film casting and cellulose cannot dissolve in water. The product of trial 3 and 4 had similar properties as both consist of a mixture of the cellulose and the disorderly-filmed long chain polymers. Moreover, Trial 5 with bleach resulted in a 16 minutes increment. From the results, it is indicated that bleach interrupts the formation of film the most compared to the other additives that were tested. This may be due to the size of the lattice and the strong electrostatic attraction between the Na+ and ClO3- ions.

There is no vulcanization between those ions and the long chain starch polymer.

Consequently, the bleach additive trial did not result in a solid state as was the case in the other trials but stayed in a rather transparent transitional state. The appearance of the trials also became less transparent due to the un-dissolved paper pulp (cellulose). While trials 1,2 and 6 had a transparent appearance, trial 3 had a milky white appearance and trials 4 and 5 both had a very dark brown colour. This colour variance is primarily caused by the impurities inside the paper that had not been eliminated during the experimental process. Trial 4 had more ink contaminants. The reason behind the dark brown appearance of the bleach trial is not yet understood and all four alternative trials on bleach had shown no effect on the removal of the ink pigment.

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2. SEM Analysis Fractured surfaces, as a result of bending, stretching and pinning from the mechanical test, were studied using SEM and all the relevant photos are present in Fig 3, Fig 4, Fig 5 and Fig 6. Fig 3 shows the morphological aspects of the original trial (cooled under standard conditions). The surfaces with no additives reveal a significant amount of stretching and cracks. The cracks observed were usually longer than 1mm. The same trend can be observed in soap additives plastic heated to 45!C. However, this plastic has cracks that were smaller in both width and depth. Moreover, the cracks were observed more of a random pattern in comparison to the non-additive control. These results demonstrate that the poor mechanical properties of starch plastic with no additives resulted from a lack of adhesion on the microscopic level. From the results, it can be deduced that effective heating during crystallization assists the formation of patterns in the starch and thus may improve overall mechanical properties of the plastic.

The greatest improvement in microscopic level structure was in the trials with paper additives (newspaper and paper towel). The two paper additives trials had little differences in both pattern and crack appearance. Both of the trialsâ&#x20AC;&#x2122; surfaces became smooth with no clear pattern. It can thus be concluded that ink chemicals have little effect on microscopic level structure. The number of cracks decreased substantially and cracks observed tend to be very short, small and shallow. The cracksâ&#x20AC;&#x2122; length varies from 50!" to 150!!"! The reduction in cracks number and length of cracks explains the stronger mechanical properties of those two trials in comparison to the non-additive control. The graphs in the next four pages (P8-11) are organised horizontally where sign A, B and C represent the two pictures beside each other.

FIG 2. The samples tested in SEM

a) Trial 1 with no additive

b) Trial 2 with soap additive and heating

c) Trial 3 with paper towel additive

d) Trial 4 with newspaper additive 41

A

B

C

FIG 3. SEM micrograph of trial 4 with no additives (A) 80x (B) 200x (C) 2000x

A

B

FIG 4. SEM micrograph of trial 6 with soap additives (A) 80x (B) 200x (C) 2000x

42

C

A

B

C

FIG 5. SEM micrograph of trial 7 with paper towel additives (A) 80x (B) 200x (C) 2000x

A

B

C

FIG 6. SEM micrograph of trial 9 newspaper additives (A) 80x (B) 200x (C) 2000x

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3. Mechanical Properties Test The effect of different additives such as newspaper and bleach, on the mechanical properties of the starch-based bio-composite plastic was investigated. Figures 8 to 11 summarize the force-extension results and relevant calculations are carried out to determine the Young Modulus. The effect of heating alone on the plastic was not carefully monitored and evaluated. From the results, a clear increment in both tensile strength (4.94MPa and 0.22MPa) and Young Modulus (30.06 MPa and 7.66MPa) can be seen in the newspaper additive in comparison to the non-additive control. This result is consistent with the SEM analysis results, which showed that newspaper additive, specifically with the addition of cellulose, improved the overall mechanical properties of the plastic.

The tensile properties of paper towel additive, on the other hand, show negligible increment in both modulus (8.08MPa and 7.66 MPa) and strength (0.47MPa and 0.22 MPa).

This result is most likely be caused by the uneven distribution of paper towel in the sample as it was added manually. Furthermore, the paper towel sample test was only carried out once due to the limited availability of materials. Therefore, the uncertainty in the result was undefined and thus may be unreliable.

Heating the soap additive for faster solidification revealed to have increased the strength (2.45MPa) and modulus (18.46MPa) of the plastic. It is highly unlikely the soap additive will have an effect on the mechanical properties as its chemical composition has no interaction with the starch polymer chain. The heating effect may reduce the percentage of water in the composite and thus reduce the distance between the polymer chains. However, the result may again be unreliable due to the limited number of testing trials.

Contrasting with PLA, the starch-based plastic has generally a lower strength and Young modulus. Normal PLA has a tensile strength around 40-60 MPa and a Modulus of 3000-4000 MPa. The value of newspaper additive is 9.88% strength and 0.86% Young Modulus of the value of PLAâ&#x20AC;&#x2122;s strength and Young Modulus. The lack of strength and modulus may be remedied through a more concentrated addition of newspaper. Nevertheless, it is highly unlikely to achieve such high value without effective chemical treatment.

FIG 7. RGM-4100 for mechanical tests

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Table 2. Mechanical properties of newspaper additives

Sample Name

Reger_BH_001 Reger_BH_001 Reger_BH_001 Reger_BH_001 Maximum Value Minimum Value Average Value Standard Deviation Coefficient of variation (%)

Original Length

Width

Height

Area

mm

mm

mm

mm2

25 30 25 25

5.82 11.40 5.06 5.87

1.02 1.15 1.15 1.16

5.94 11.63 5.82 6.81 11.63 5.82 7.55 2.39 31.61

Largest Load (Fm)

Young Modulus (E) MPa

Elongation at break

N

Tensile Strength (Rm) MPa

31.77 61.81 27.29 30.05 61.81 27.29 37.73 14.00

5.35 5.32 4.69 4.41 5.35 4.41 4.94 0.40

26.81 29.53 30.62 33.28 33.28 26.81 30.06 2.32

19.50 19.50 16.00 14.50 19.50 14.50 17.38 2.19

37.10

8.15

7.71

12.61

%

FIG 8. Force Against Extension Graph of newspaper additive Table 3. Mechanical properties of non-additive Sample Name

Reger_BH_001 Maximum Value Minimum Value Average Value

Original Length

Width

Height

Area

Largest Load (Fm)

Tensile Strength (Rm)

Elongation at break

MPa 0.22

Young Modulus (E) MPa 7.66

mm 27

Mm 5.50

mm 6.72

mm2 36.96

N 8.01

36.96 36.96 36.96

8.01 8.01 8.01

0.22 0.22 0.22

7.66 7.66 7.66

5.50 5.50 5.50

FIG 9. Force Against Extension Graph of non-additive 45

% 5.50

Table 2. Mechanical properties of soap additive with approximately 50!C in oven for a day Sample Name

Reger_BH_001 Maximum Value Minimum Value Average Value

Original Length

Width

Height

Area

Largest Load (Fm)

Tensile Strength (Rm)

Young Modulus (E)

Elongation at break

Mm 25

mm 4.96

mm 3.60

mm2 17.86 17.86

N 43.74 43.74

MPa 2.45 2.45

MPa 18.46 18.46

% 17.50 17.50

17.86

43.74

2.45

18.46

17.50

17.86

43.74

2.45

18.46

17.50

FIG 10. Force Against Extension Graph of soap additive with approximately 50!C in oven for a day Table 3. Mechanical properties of paper towel additive Sample Name

Reger_BH_001 Reger_BH_001 Maximum Value Minimum Value Average Value Standard Deviation Coefficient of variation (%)

Original Length

Width

Height

Area

Largest Load (Fm)

Tensile Strength (Rm)

Young Modulus (E)

Elongation at break

Mm 30 30

mm 10.2 10.5

mm 3.4 3.0

mm2 34.68 31.50 34.68

N 19.46 11.62 19.46

MPa 0.56 0.37 0.56

MPa 9.07 7.08 9.07

% 35.00 15.50 35.00

31.50

11.62

0.37

7.08

15.50

33.09 1.59

15.54 3.92

0.47 0.10

8.08 1.00

25.25 9.75

4.81

25.21

20.65

12.33

38.61

46 FIG 11. Force against extension graph for paper towel additive

4. Antiseptic Test The effect of different additives on limiting bacteria growth had been recorded over a 3-day interval. The resulting photos are shown in Fig.12 and Fig.13. All three trials exhibit some extent of bacteria growth on the plastic. The no additives control had significant growth after four days with dark spots appearing near the plastic. The paper additive, on the other hand, had also experienced bacterial growth near the plastic in the second observation.

However, the spots were more widely spread and dissolved into the plastic. The soap had limited the growth in the first 3-day interval but failed in the second interval. White colonies of bacteria appeared next to the plastic and the plastic undergoes rapid decomposition. The agar dish became misty and hard to recognize. From these results, it can be deduced that soap had a limited long-term effect on prohibiting the growth of the bacteria. Long lasting effect of soap on the resistance of bacteria in the plastic needs further exploration. The addition of bleach was not considered due to the unsuccessful solidification of the plastic.

FIG 12. Antiseptic results Day 1

FIG13. Antiseptic results after 4 days

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V.

CONCLUSION

In this study, the possibility of manufacturing a bio-composite plastic has been tested with a range of targeted aims. Different obtainable additives: bleach, paper towel, soap, and newspaper were tested. The appearance, mechanical properties and antimicrobial of this biodegradable plastic with additives were investigated using agar dishes, a Young Modulus testing machine and SEM techniques. A much-required stable Tf (100 °C) throughout the experiment indicated a promising stability in energy and temperature requirements. Thus, the cost for processing in terms of energy can be calculated with small uncertainty. The duration for drying and crystallization for most of the trials were around 2-3 days, which suggests a fast cycle of production. A higher ambient temperature for drying purposes is favourable for the formation of the biodegradable starch plastic, which widens the application of this plastic in countries near the equator as they have longer periods of daylight. Furthermore, biodegradation of those bio-composites could take place as soon as one week, if left outside in the open.

The SEM morphology test showed a positive result with paper additives in microscopic level analysis. The number of cracks and gaps on the surface were reduced effectively compared to the non-additive control. In addition, the plastic had a better performance in flexibility in comparison with the control sample. These improvements were the result of the addition of cellulose, which provided more crossovers between particles in molecular level over the film casted.

The mechanical property test results reaffirmed the results from the SEM test. The newspaper additive was indicated as having the highest tensile strength and Young Modulus throughout all the samples. The improvement was predicted to be primarily caused by cellulose inside the newspaper. This can be tested by extracting the cellulose through acid and oxide hydrolysis during the extraction process [12]. However, studies indicate that cellulose nanofibre-based materials have exhibited high biodegradability and excellent mechanical properties as well as low toxicity, which make it the most ideal additive to the plastic [16]. Other important factors such as the concentration of the additive, the concentration of the paper towel, and heating were not carefully controlled in the experiment.

This may lead to a biased result and may require more investigation of the effect of those factors. The perfect ratio of additive and blend may also play a role. It can be deduced from the results that effective heating will enhance the mechanical properties but lower the flexibility of the plastic. A higher concentration of additive such as paper (cellulose mainly) is also favourable for a better mechanical performance. However, the paper used in the experiment is newspaper, which is already processed and hence difficult to relate the improvement in mechanical property to a specific substance inside the newspaper. Moreover, the ink pigments that result in the brown opaque appearance of the plastic may be removed from the paper through chemical treatment before adding to the plastic in the future, which will significantly enhance its appearance. Further experiment and investigation is required to determine the substance responsible for the improvement in mechanical properties and extract it in vast quantity for mass production of this biodegradable plastic. The specific type of cellulose used as the additive may be an area for additional research. It is proposed that milkweed stemâ&#x20AC;&#x2122;s fibres have a higher content of cellulose compared to rice straw, wheat and most other lingo-cellulosic by-products as well as requiring less treatment [13]. However, milkweed stem is mainly found in North and Central America, which may require further consideration, such as transportation and potential harm to the local eco-system, if distributed and planted to less-developed economies.

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The agar dish test results showed a potential application of antiseptic usage in biodegradable plastic but still require further experiments to improve the performance and long lasting effect of the additives. The effect of soap additive disappeared after 3 days and the growth of bacteria increased to a standard similar to the other non-soap additive trials.

The bleach trial demonstrated another potential additive to the plastic that requires more investigation. The time duration for formation of the plastic increased by 106% compared to the non-additive control. This may be caused by the lack of linking between the bleach and the polymer, as the strong attraction between the ions in bleach is not overcome by the energy provided. Direct addition of bleach to the plastic, as bleaching agent, proved to have no effect on getting rid of the dark brown colour of the newspaper additive. Other treatments to the newspaper may be needed to achieve this aim. A potential danger of using bleach as an additive may be the release of Clâ&#x2C6;&#x2122; free radicals after long-term biodegradation. In fact, the availability of bleach is not as common as the other sources of materials used in the entire experimental process and thus may raise the cost of the plastic to a level where it is not affordable in many less developed countries.

The transformation of cornstarch into soluble starch indicates a path for further development of starch-based plastic. The cornstarch after 1 month in excess vinegar solution began to behave like a soluble starch at the beginning of the manufacturing process but the product at the end was still very difficult to shape and solidify. If the transformation could be done more quickly than immersing cornstarch in vinegar but with no specific chemical treatment, the manufacture of starch-based plastic will be more feasible and practical in developing countries.

In conclusion, the starch-based plastic, with its excellent flexibility in shaping, has a variety of potential applications in the less-developed countries. Additives, such as newspaper, soap and bleach, are readily available inputs that can be implemented to enhance the final biocomposite properties for a targeted function such as seed storage for agricultural purposes. Moreover, the relatively simple method of production may be widely taught throughout a country with almost no need for understanding the scientific techniques of each processing step. The large number of different additives to the plastic suggests a range of improvement in different aspects of the plastic and therefore a multitude of applications in the less developed countries.

ACKNOWLEDGEMENT The SEM morphology and mechanical test were performed in Shenzhen Universityâ&#x20AC;&#x2122;s Engineering lab. The department of material science is gratefully acknowledged for technical support. The author is also thankful to Mrs. Cliffe for providing the experiment with all essential equipment and the fruitful discussion for potential development of the investigation and Mrs. Morris who acted as the Centre coordinator. The author especially appreciates the discussion with Mrs. Smith, who acted as the supervisor and examiner. Those discussions provided tremendous help throughout the experiment and finalizing process of the report.

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50

Investigating the stretching of a Slinky produced by its own weight Greg Chu1, Dr Michael Daniel2, Courtney Lam3 Harrow International School Hong Kong

The Slinky is an example of a loosely wound spring, which is capable of oscillating vertically under the influence of gravity without having an additional mass hanging at the end of it. In this article, we are going to investigate how much a Slinky is stretched when it is fixed at one end and is allowed to hang vertically under the action of its own weight.

( ( ( ( ( ( ( (

The spring constant of a fraction of a spring If a spring has a spring constant k, what is the spring constant of a fraction of the spring?

To answer this, we regard the spring of length L to be equivalent to n springs of length L/n, all connected in series. A force F acting on the spring of length L will produce an extension !x, which is equal to the sum of the extensions of the n springs of length L/n, also f is the fraction of the whole spring, therefore f=1/n !! !

!

!!!

!!!

From Hookeâ&#x20AC;&#x2122;s law !x = F/k and !xi = F/kf. Hence, ! ! ! ! !!

Consequently, the spring constant of a fraction of a spring, whose spring constant is k, is given by

51

!! ! !" !

! ! !! ! ! !

The stretching a Slinky under its own weight

When a Slinky is hung vertically from one end, it will stretch under its own weight. We would like to calculate by how much a Slinky of length L and mass m will be elongated, when is allowed to hang vertically at equilibrium.

y y+! y+"y +++++++y!

Consider a section of the Slinky between y and y+!y. When the Slinky is hanging vertically in equilibrium, this section will be extended by "y. Let Âľ be the mass per unit length of the Slinky. The mass of the section of the Slinky between y and y+!y, which is in equilibrium, is subject to the pull of gravity downwards, the pull of a tension T (acting at y) upwards and the tension T-!T (acting at y+!y) downwards. Hence, ! ! ! ! !! ! !!"# ! !

(1)

From Hookeâ&#x20AC;&#x2122;s law, the extension "y of this section of the Slinky satisfies ! ! !! !

!

!! !

!"!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!!(2)

The tension T is the weight of the mass of Slinky corresponding to the section of the Slinky of length L-y. Hence, ! ! ! ! ! !" ! ! !

! !

!" ! ! ! ! !"

(3)

where, f, the fraction y/L of the total length of the Slinky. Using equations (1), (2) and (3) we obtain ! ! ! !"!! ! !!"#!! ! !"# In the limit !f # df, and "y # dy, we finally obtain

52

(4)

!" !

1 − ! !" = !"

(5)

Integrating equation (5), with the condition that the tension vanishes at the lower end of the Slinky gives !" !

!−

!! !

= !(!)

For f=1, equation (6) gives !! ≡ ! 1 =

(6) !"

2!

Hence, the length of the Slinky elongated under the action of its own weight is L+y0.

(

The stretching of a Slinky with a mass M suspended at the end of it In this case, the Slinky is elongated under the action of its own weight and the weight of the attached mass M at the end of it. Consequently, equation (6) is modified and now reads !! !" !" !− + ! = !(!)

2 ! !

(7) For f=1, equation (7) gives

!

!"

!

!!

!= !+

(8)

The total length, l, of the slinky with mass M attached at the end is given by !

!"

!

!!

!= !+

+!

(9)

By varying M and measuring l it is possible to plot a graph of l against M. Equation (9) shows that a graph of l against M should give a straight line with gradient equal to g/k and !" intercept + !. !!

53

Experiment The Slinky used in the experiment had 70 coils with a non-stretched length L=0.055m and mass m=0.212kg.

Measuring the extension of the slinky

Data ;$77#</=>?&?@#

A!./"3#<4=>?&??@#

#

!"#$%&'&

!"#$%&(&

!"#$%&)&

*+$,&-$%.+&

11.13#

1.066#

1.069#

1.067#

1.067#

21.12#

1.162#

1.165#

1.166#

1.164#

31.15#

1.269#

1.267#

1.268#

1.268#

41.11#

1.369#

1.366#

1.370#

1.368#

51.15#

1.468#

1.471#

1.474#

1.471#

61.16#

1.573#

1.565#

1.569#

1.569#

54

l vs. M 1.8 y = 10.082x + 0.9551

1.6 1.4

l(m)

1.2 1 0.8 0.6 0.4 0.2 0 0

0.01

0.02

0.03

0.04

0.05

0.06

0.07

M(kg)

From the equation of the best-fit line we deduce that ! ! !"!!"!!!!"

(10) ! !"

! ! ! !!!""!!

(11) With L=0.055m equations (10) and (11) give a value for the mass of the Slinky, m, to be equal to ! ! !!!"#!!" !!

This is less than 0.212kg, which is the mass of the slinky measured directly with the use of an electronic balance. The difference can be accounted for, if we take into account the Slinky’s pre-tension. For the Slinky to start stretching under the action of its own weight you have to apply enough force to overcome the “excess” spring force that is keeping the slinky collapsed. This minimum force is called the pre-tension. For the Slinky used in our experiment the pre-tension is equivalent to the weight of 9±1 coils of the 70-coil slinky. This means that the effective mass of the Slinky is given by !""#$%&'#!!"## ! !!!"! ! !

! ! !!!"# ! !!!!" !" !"

which is comparable to the value of 0.179kg obtained from the analysis of the experimental data shown above.

References 1 Year 12 (Peel) 2 Teacher of Physics 3 Year 12 (Gellhorn)

55

The effect of non-alcoholic drinks on L. casei Shirota from Yakult in non pH-regulated gastric simulation in vitro Ryan Thang1 Harrow International School

Preamble ( Yakult, a commercial probiotic drink, contains the bacterial strain Lactobacillus casei Shirota (henceforth referred to as L. casei S). Due to its relatively small volume of drink per bottle (125mL), consumers may choose to consume another drink after Yakult. This investigation aims to observe how some of these drinks consumed after Yakult impact the growth of L. casei S such that the probiotic effect of Yakult can be fully utilised.

Experimental design ( The investigation is planned to be conducted in three distinct phases to tackle the aim of the investigation: 1. Growing the L. casei S in different concentrations of aqueous Yakult solutions to determine qualitative results of how L. casei S would appear when plated on agar.

There is a concern it may have to be isolated from other bacteria before being able to grow it in vitro. The optimal concentration of Yakult to be used should be found in this phase and it will be expected that a fewer amount of L. casei S would grow later due to the conditions it would be grown in.

2. Growing L. casei S in simulated oral and stomach conditions to determine suitable simulated stomach conditions for the L. casei S, as factors such as gastric pH is dependent on many factors. It would be expected that in certain trials, there may be no L. casei S growth at all as some conditions may be too harsh. The concentration of Yakult used may be changed if none of the proposed models for stomach conditions are possible.

3. Growing L. casei S in simulated oral and stomach conditions with food substances to compare the growth of L. casei S in different types of food and beverage and hence make up the bulk of experimental data. The data will be used to formulate a conclusion to the investigation, and is aimed to allow people to make more informed choices as to what they might want to consume alongside Yakult in order to fully take advantage of the probiotic effect of L. casei S.

56

The first trial (Phase 1) ( Preface: Finding out what they look like compared to an agar plate confirmed to have L. casei S, as well as the amount of L. casei S in Yakult would enable the rough determination of how much Yakult is needed, as well as testing if colony counting is practical.

Results and evaluation: For (1) and (3) there was no visible growth of any microorganism, but for (2) there was a blue-black patch of what was assumed to be fungi. Essentially, the trial yielded no visible L. casei S and so was considered a failure. Temperature should not have been a problem as it was close to the optimal range of 35˚C 1. It is expected that in anaerobic conditions, they should grow adequately 2.

The second trial (Phase 1) ( Preface: MRS agar will be used in this trial 3,5. Concentrations of 5% (4), 1% (5) and 0.1% (6) will also be used. The temperature of 37˚C is used, which was the greatest accuracy of temperature (±1˚C) that could be used based on evidence suggesting that mean human body temperature is at 36.8˚C4.

Results and evaluation: The best to observe growth was (6) as it gave a number of easily countable colonies (102 colonies) and they were not too closely distributed to each other. Figures 1-6 show growth of L. casei S after 7 days of incubation for (1) to (6) respectively. Note that this is 3 more days than the intended 4 days of growth.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

57

The third Trial (Phase 2) ( Preface: Human gastric fluid is in the range of 1.5-3.5 pH 6. Mean human salivary α-amylase (ptyalin) is 2.64mg/mL 7. To simulate oral conditions, an aqueous solution of 2.64mg/mL of ptyalin is made up. To simulate stomach conditions, the use of USP (United States Pharmacopeia)Gastric fluid, simulated, test solution (henceforth referred to as “Simulated gastric fluid TS”) was proposed, containing 2 mg/mL of NaCl, 3.2 mg/mL of pepsin, and 0.06M solution of HCl 8. It was decided that a range of 0.01-0.06M HCl would be used.

A pilot test was run where only the ptyalin solution was tested to ensure that it did not immediately arrest the growth of L. casei S. Figures 7 and 8 show the plates without the ptyalin solution and with it respectively. There were no visually significant effects of using the ptyalin solution as there were still bacterial colonies growing in the agar.

Figure 7 Figure 8

Results and evaluation: All plates had colonies, but there was a trend seen that as the concentration of HCl increased, the number of colonies decreased. 0.01M of HCl (pH 2) had the most number of colonies and hence would give the greatest accuracy of results while being in the range of human gastric fluid. As a result, this concentration of HCl will be adopted in future experiments.

The fourth trial (Phase 3) ( Preface: After determining the appropriate conditions to grow the L. casei S in, a trial went underway to grow the culture with food substances included in the solution. It was arbitrarily decided that white bread would be the solid food product, and Vita Lemon Tea (VLT) and Ribena would be the liquid food products to test growing L. casei S. Results and evaluation: 58

Plate Number 1 2 3 Mean (±σ)

Number of colonies per plate Water (Control) VLT 258 517 232 284 172 340 221 (±44) 380 (±122)

Ribena 181 118 205 168 (±45)

There was a large range of the number of colonies in the different test substances. It was a time-consuming process to count all the colonies of each of the agar plates. Bacterial colonies were obscured by pieces of bread, which made it impossible to count the number of colonies that grew. Using solid food substances is not a viable idea as there is no uniform way to compare food substances and beverages other than by mass, which is also not a suitable method as the different food and drinks have different densities, and so would affect the concentrations of the other components in the solution.

Whilst there is data gathered for each test substance, the standard deviation varies considerably, giving up to 32.1% error in the worst case (VLT mean value). This may be very likely due to inconsistency in plating techniques and inconsistent volume of solution used. As a result, using solid agar medium is not a viable method.

The fifth trial (Phase 2) ( Preface: A new model is proposed, where a liquid medium (MRS broth) would be used instead of an agar plate. This allows the conditions to be more carefully controlled and a more accurate quantitative method to be used.

Limitations due to equipment only allow OD590 to be measured instead of the standard of OD600. Using OD is based on the principle of the Beer-Lambert Law expressed as A=Log(I0/I1) where A is absorbance/optical density, I0 is the incident intensity and I1 is the transmitted intensity of light. This is applied here as the bacterial growth increases, scattering of light increases, and I1 decreases and results in a higher absorbance value, and vice versa.

Results and evaluation: Test tube number OD590 Water (Control) Before incubation 0.23 After incubation 1 2.00 2 1.52 3 Mean 1.76

Ribena 0.18

VLT 0.13

2.00 2.00 1.82 1.94

2.00 2.00 1.94 1.98

Results of many samples went beyond the highest measurable absorbance of 2.00, meaning growth beyond a measurable limit. There was also a problem with dissolving the, as the

59

solubility of pepsin in deionised water is limited to 10mg/mL 9. To tackle both the problems of over-growth and undissolved pepsin, the original solution (4mL of MRS broth, 1.5mL of more concentrated simulated gastric fluid TS, 2.5mL of test substance, 1mL of ptyalin solution and 50µL of Yakult), will be changed to a new solution (3mL of MRS broth, 3mL of more concentrated simulated gastric fluid TS, 3mL of test substance, 1mL of ptyalin solution and 50µL of Yakult).

The sixth trial (Phase 3, final trial) ( Preface: This final trial is planned to obtain results for the following drinks: distilled water, Ribena Blackcurrant Fruit Drink, VLT, Vita Malted Vitasoy, Vita Chocolate Milk, Schweppes Soda Water, Coca-Cola Zero, 7-Up, Schweppes Tonic Water, Schweppes Cream Soda. Packaging information of the drinks are shown in figures 9 to 17.

Method: 1. Mix MRS broth solution and more concentrated simulated gastric fluid TS in a 1:1 volumetric ratio, making up 6mL of this combined solution per test tube being used, and stir well. Put 6mL of this combined solution in each test tube being used.

2. Mix Yakult and ptyalin solution, with Yakult added to the 50µL/mL ptyalin solution, making up 1mL of this combined solution per test tube being used, and stir well.

3. Add 1mL of the solution from step 2 to each of the test tubes used in step 1.

4. Add 3mL of test substance to each test tube being investigated for each test substance, and gently swirl the test tube well to mix. Label test tubes accordingly.

5. For each test substance, select a test tube and dilute samples with deionised water in a 1:9 volumetric ratio of sample to deionised water. Put the diluted samples into cuvettes, and measure absorbance at 590 nm.

6. Incubate at 37˚C for 1 week.

7. Shake test tubes thoroughly and dilute samples with deionised water in a 1:9 volumetric ratio of sample to deionised water. Add each diluted sample into cuvettes and measure absorbance at 590 nm. Compare absorbance before and after incubation.

Drink (1) Distilled water *(control) (2) Ribena- Blackcurrant Fruit Drink (3) VLT (4) Vita Malted Vitasoy

Sugar content (g/100mL) 0

OD590 After/OD590 Before (%) 160.00

t-test t value n/a

Change in OD590 compared with control (%) n/a

11

88.89

1.1315

55.56

13.6 6.5

166.67 84.66

0.1078 1.2311

104.17 52.91

[10]

60

!"#$%&'($')*+,-'./01#2&3'4/' ./$42/5'678'

>(%:2&'<,'

*"##$##%&

*###$##%& )##$##%& (##$##%& '##$##%& "##$##%& #$##%&

!"##$##%&

#&

"&

(5) Vita Chocolate milk (6) Schweppes Soda water (7) Coca-Cola zero (8) 7-up (9) Schweppes Tonic Water (10) Schweppes Cream Soda

'&

10.4 0 0 7.7 8.9 11.7

(&

)&

*#&

9:%#2'./$4&$4'6%;<--0=8'

87.50 219.05 123.81 633.33 533.33 1900.00

1.1776 0.8255 0.5801 3.003 3.4797 8.0203

*"&

*'&

*(&

54.69 136.90 77.38 395.83 333.33 1187.50

Results The relationship between each drink and OD590 of the solution after incubation compared to the control is shown in figure 18, including bars indicating upper and lower bounds. It can be observed that drink (10) produced the highest OD590 compared to the control, while drink (4) produced the lowest comparative OD590. The growth of L. casei S, the relationship between sugar content and OD590 compared to the control is represented in figure 19. While it may seem that there is a positive correlation, a two-tailed spearmanâ&#x20AC;&#x2122;s rank correlation coefficient test was carried out with a significance level of 95%, showing a value of 0.1779 hence showing no significant correlation between the sugar content and OD590 of the solution after incubation.

For testing H0: There is no significant difference between the change of OD590 value of the test drink and the change of OD590 for the control, an unpaired two-tailed t-test was used with a 5% significance level and 4 degrees of freedom, and the only statistically significant results were for (8), (9) and (10), as they all had t values above 2.78. Thus for (8) to (10), H0 was rejected.

Discussion ( Several potential inaccurate results were identified in this investigation, including results with OD590 values )0.01 or *0.1. This is due to the relationship between the Beer-Lambert Law, concentration of L. casei S in the solution and precision of the colorimeter used in this investigation.

The Beer-Lambert Law states that T=10-A hence A=-Log(T), where T is the transmission of light and A is the absorbance of light in the solution. Values of OD590 ) 0.01 are prone to inaccuracy as it is the minimum scale of the instrument. To avoid this in the future, a more precise colorimeter or spectrophotometer may be used instead. Values of transmission were 61

not measured in this investigation; so further detail into absorbance values is not possible through the use of the Beer-Lambert Law. Values of OD590 * 1.00 are also inaccurate as the relationship between concentration of bacteria in suspension and absorbance are non-linear above absorbance of 1.0011.

Due to this, the results for (4), (5), (8), (9), (10) before incubation and (4), (5) after incubation were inaccurate. However, with the analysis of the amount of error, results with values of OD590 can still be analysed and discussed. The values for (4) and (5) can be considered very inaccurate, even showing high turbidity after a dilution by a factor of 10. These two sets of data will be omitted from discussion, except for the evaluation of this investigation. If such an investigation were to be repeated, a calibration curve may be drawn to show the relationship between the dilution of any substance and the resulting OD590 value so that highly turbid solutions such as (4) and (5) can be diluted to give accurate results.

As (8), (9), and (10) had an OD590 of 0.01 before incubation, the upper bound for the change in OD590 became very high. As mentioned in the previous trial, not diluting it by a factor of 10 would cause many of the results to have an OD590 above 1.00. In this trial, the tested drinks were the cause of the OD590 being more than 1.00, and the values of 0.01 were not encountered in the previous trial.

For both (4) and (5), the OD590 decreased, which could mean that the solution became less turbid. Figure 20 shows the appearance of the solution before incubation after dilution by a factor of 10; figure 21 - the solution after incubation; and figures 22 and 23 - the solution after incubation and dilution by a factor of 10, and note that the solutions for (4) and (5) were not diluted yet. All figures show the solution with drinks (1) to (10) from left to right. These highlight one of the major limitations of the method: it is assumed that any particles or colouring agents in the solution that cause light scattering or absorb 590nm wavelength light are not affected by L. casei S. However, as the independent variable consists of many components (for example sugar and flavouring agents), determining the growth of L. casei S

!"#$%&'($')*+,-'./01#2&3'?(4"'./$42/5'678''

>(%:2&'<C' "+##$##%& "###$##%& *+##$##%& *###$##%& +##$##%& #$##%&

*2($@A'6<B<-8'

62

in such a complex environment cannot solely be found by colorimetric methods or strictly counting colonies. A different technique of growing bacteria may need to be developed in order to facilitate such an investigation.

Nevertheless, based on currently obtained data, (10) increases growth the most, followed by (8) and then (9). As a result, it may be beneficial to consume any of these after Yakult.

Values for (2) to (7) cannot be confirmed to be statistically different from the control (1) so they may be investigated further into in order to fully determine their relationship with L. casei S.

Figure 20

Figure 21

Figure 23

Figure 22

Conclusion While the drinks (8), (9) and (10) appear to promote the growth of L. casei S the limitation that any colouration in the drink could be affected by L. casei S may render the investigation invalid. This phenomenon may warrant further investigation to ensure that the results in this investigation are valid. As for (2) to (7), the results were inconclusive due to no significant differences compared to the control (1).

In addition to this, the reality is that other food and drink will be consumed alongside Yakult, so the results from this investigation may not represent what actually happens in the human stomach. This is further shown, as the conditions of the growth of L. casei S were not constantly regulated. Improvement of the methods in future similar investigations could include either the development of a new technique to measure bacterial growth, using automated equipment such as a bioreactor to grow L. casei S, using more precise instruments and /or factoring in how the growth of L. casei S could affect colouration of the food used in the investigation.

63

References 1

Year 13 (Peel) 1. Oh S, Rheem S, Sim J, Kim S, Baek Y (1995) Optimizing Conditions for the Growth of Lactobacillus casei YIT 9018 in Tryptone-Yeast Extract-Glucose Medium by Using Response Surface Methodology. Applied and Environmental Microbiology 61(11), 3809-3814 2. Zotta T, Ricciardi A, Ianniello RG, Parente E, Reale A, Rossi F, et al. (2014) Assessment of Aerobic and Respiratory Growth in the Lactobacillus casei Group.

PLOS ONE 9(6): e99189. DOI: https://dx.doi.org/10.1371%2Fjournal.pone.0013352 3. Sigma-Aldrich (2013) Product Information 69964 MRS Agar (Lactobacillus Agar acc. to De Man, Rogosa and Sharpe). St. Louis, Missouri, USA. Retrieved from: http://www.sigmaaldrich.com/content/dam/sigma-aldrich/docs/SigmaAldrich/Datasheet/1/69966dat.pdf 4. Mackowiak PA, Wasserman SS, Levine MM (1992) A Critical Appraisal of 98.6°F, the Upper Limit of the Normal Body Temperature, and Other Legacies of Carl Reinhold August Wunderlich. JAMA. 268(12):1578-80, DOI:10.1001/jama.1992.03490120092034 5. De Man JC, Rogosa M, Sharpe ME (1960) A medium for the cultivation of Lactobacilli. Journal of Applied Bacteriology 12(1): 130-35 6. Marieb EN, Hoehn K (2010). Human anatomy & physiology. San Francisco: Benjamin Cummings. ISBN 0-8053-9591-1 7. Mandel AL, Peyrot des Gachons C, Plank KL, Alarcon S, Breslin PAS (2010) Individual Differences in AMY1 Gene Copy Number, Salivary ι-Amylase Levels, and the Perception of Oral Starch. PLoS ONE 5(10): e13352. DOI: https://doi.org/10.1371/journal.pone.0013352 8. Abrahamsson B, Ungell AL (2009) Biopharmaceutical Support in Formulation Development. M. Gibson (Ed.), Pharmaceutical Preformulation and Formulation: A Practical Guide from Candidate Drug Selection to Commercial Dosage Form (2nd ed.) (pp. 247-288). New York, NY: CRC Press.

9. Sigma-Aldrich (2016) Pepsin. St. Louis, Missouri, USA. Retrieved from: http://www.sigmaaldrich.com/life-science/metabolomics/enzyme-explorer/analyticalenzymes/pepsin.html 10. FairPrice((2017)(Ribena&Ready3To3Drink&B'Currnt&Reg&6S&200ML&Product& Description.(Singapore,(Singapore.(Retrieved(from:( http://www.fairprice.com.sg/webapp/wcs/stores/servlet/ProductDisplay?storeId=1 0001&productId=37290&urlRequestType=Base&catalogId=10051( 11. Lerchner J, Schulz A, Poeschel T, Wolf A, Hartmann T, Mertens FO, Boschke E (2012) Chip calorimetry and biomagnetic separation: Fast detection of bacterial contamination at low cell titers. Engineering in Life Sciences 12(5):1-6, DOI: 10.1002/elsc.201200029

64

The biggest overhang with n one metre rulers Dr Michael Daniel1, Katrina Tse2 and Zeli (Benjamin) Wang3 Harrow International School Hong Kong

First, we are going to assume that the rulers are identical and they are uniform in density.

This means that their mass is uniformly distributed. We are also going to assume that only one ruler occurs at each level and all the rulers are in one plane. Later on, we are going to relax this assumption and consider cases where more than one ruler occurs at each level.

Derivation of formula for the maximum overhang with n rulers Let xn be the overhang achieved with n rulers as shown in Fig. 1. This is achieved by having the centre of mass, Gn, of the n rulers taken together to be directly above point A, which is the corner of the base relative to which we are measuring the overhang.

Let us now add another ruler, the (n+1) th ruler, to above arrangement. We can slide the entire arrangement of the initial set of n rulers over the (n+1) th ruler so that the centre of mass of the (n+1) rulers, Gn+1, is now on top of A. In this arrangement the centre of mass, Gn, of the initial set of n rulers is shifted horizontally by a distance x . See Fig. 2.

The arrangement in Fig. 2 will be in equilibrium if x satisfies !

! ! ! ! !"# !

where m is the mass of a single ruler. Hence, with (n+1) rulers we have an overhang of xn+1, which satisfies the equation

65

! ! !!!! ! ! ! !! ! !!!

If we use the fact that the overhang achieved by using a single ruler is !, the above equation has a solution given by ! ! ! ! !! ! ! ! ! ! ! ! !! ! ! ! ! where Hn is the nth harmonic number given by

where $ = 0.57722

! !! ! !"#! ! ! ! ! !! ! !

Alternative derivation The one metre rulers can be modelled as massless rods of unit length with two unit masses fixed at both ends. Let E1, â&#x20AC;Ś, En be the extensions of the n rulers. To maximise the overhang the n rulers rest in equilibrium on the support Sn. This means that the centre of mass of the n rulers is directly above the support Sn, so that the reaction of the (n+1) th ruler acts through Sn. See Fig.3.

Fig.3 Taking moments about Sn the anticlockwise moment, An, can be recursively defined as !! ! ! ! !! ! !!!!! ! ! ! ! !! !

where 1-En is anticlockwise moment due to the nth ruler, while !!!! is the anticlockwise moment due to n-1 rulers taken about the Sn-1 support. Moving the Sn-1 support to the left by the extension En has the effect of decreasing the An-1 moment by (n-1)En. The clockwise moment, Cn, can be similarly calculated as !! ! !! ! !!!!! ! ! ! ! !! !

Equilibrium demands that An = Cn and An-1 = Cn-1 which gives ! !! ! !!

Thus, the total overhang is given by

! !! ! !! !

66

A more challenging problem If we relax the requirement that only one ruler occurs at each level, then the problem becomes much more challenging. With only three rulers the maximum overhang is equal to 1, as shown by the diagram below, Fig.4.

1

In this article, we are going to concentrate on the next case when we have four rulers at our disposal and show that in this case the maximum possible overhang is given by !" ! !!! ! !!!"#$% !

With four rulers, the biggest overhang can be achieved by arranging the rulers in the second layer so that they have a gap between them as shown in Fig. 5.

Fig.5 (G represents the centre of mass of a ruler and the distances x and y represent respectively the distance of the top ruler and the distance of the bottom ruler from the corner of the supporting base at the bottom of the diagram) The overhang in this case is equal to (1+z-y) and our objective is to find the maximum possible value for this expression.

67

To analyse the problem, we consider the ‘free body’ diagrams corresponding to the four rulers: Ruler 1(top ruler) !! + !! = !!!!!!!!! 1 where W is the weight of a ruler and F1 and F2 are the reaction forces on the top ruler from the two middle rulers Ruler 2 (left middle ruler) !! + ! = !! !!!!!!!!!!!(2) 1 − ! !!!!!!!!!!!!!(3) 2 1 1 !× = !! × − ! !!!!!!!!!!!!(4) 2 2

!×! = !! ×

where F3 is the reaction force on the left middle ruler from the bottom ruler.

Ruler 3 (right middle ruler) !! + ! = !!!! !!!!!!!!!(5) 1 − ! !!!!!!!!!(6) 2 1 1 !× = !! × − ! !!!!!!!!!(7) 2 2 !×! = !! ×

where F4 is the reaction force on the right middle ruler from the bottom ruler.

Ruler 4 (bottom ruler) !! + !! + ! = !! !!!!!!!!!!!!!!(8) !! ×

1 1 + ! + !×! = !! × − ! !!!!!!!(9) 2 2

Taking moments about A the condition for equilibrium demands that !×! + !×

1 1 − ! + ! = !× + ! + ! + !×!!!!!!!!(10) 2 2

which implies that ! + ! − 3! − ! = 0!!!!!!!!!!!!(11) Equations (1), (2) and (5) imply that !! + !! = 3!!!!!!!!!!!!(12) and using (12) and (9) we deduce that 3 !! = ×! + 4!×!!!!!(13) 2

68

However, equation (7) gives !! =

!×1/2 !!!!!!!!!!!!(14) 1 2−!

Substituting (14) in (13) we finally obtain 3 1 1 − !!!(15) != × 4 1 − 2! 2 Substituting (15) in the expression for the overhang, which is (1+z-y) we finally express the overhang as a function f(z), where f(z) is given by 11 1 ! ! = +!− !!!!!!(16) 8 4 − 8!

The condition for maximum overhang is !"(!) !"

=0

(17)

Equation (17) leads to the quadratic equation 8! ! − 8! + 1 = 0 whose solutions are != !

The solution ! = + !

! !

1 2 ± 4 2

is incompatible with eq. (11), therefore the value of z that produces a !

maximum overhang is given by ! = − !

! !

!. Substituting this in equation eq. (16) gives

!"#$%&%!!"#$ℎ!"#!!"#$%!!"#$!!"#$!% = References 1 Teacher of Physics 2 Year 10 (Keller) 3 Year 12 (Churchill)

69

15 − 4 2 8

Measuring the viscosity of glycerol Zeli (Benjamin) Wang1

Harrow International School Hong Kong

1

Abstract

This experiment measures the viscosity of pure glycerol at 22 ± 0.5 degrees Celsius by dropping steel spheres of different diameters into a cylinder of glycerol and measuring the times taken for them to descend 10 cm and 20 cm respectively.

At terminal velocity with a balance of forces, invoking Archimedes’ principle and Stokes’ law, the viscosity h determined is 1.23 ± 0.12 Pa s. This matches the viscosity of glycerol measured by Segue and Oberstar (1), which is 1.19 ± 0.05 Pa s. Uncontrolled factors such as temperature, available apparatus, and modelling assumptions all pose significant systematic errors.

2

Introduction

First, let the aim of the experiment be clarified. Let ms , rs , r, V , D, and v denote respectively the mass, density, radius, volume, diameter, and terminal velocity in glycerol of the steel sphere. Let mg be the mass of glycerol displaced and rg be the density of glycerol. Then we have the weight acting downwards on the sphere equal to W = ms g = rsV g 4 = pr3 rs g 3 1 = pD3 rs g.

6

(1)

By Archimedes’ principle, the upthrust on a body in a fluid is equal to the weight of the fluid displaced by the body, we also have U = mg g = V rg g 1 = pD3 rg g.

6 70

(2)

Assuming the sphere is not dropped near to the side of the cylinder, and the flow around the sphere is laminar, Stokesâ&#x20AC;&#x2122; law dictates that the viscous drag on the sphere due to the glycerol is F = 6phrv = 3phDv.

(3)

When the sphere descends at terminal velocity, it has no acceleration so there is no resultant force acting on it. Therefore by Newtonâ&#x20AC;&#x2122;s first law, the upthrust and drag opposes the weight exactly, so combining the above yields F =W U 1 1 3 3phDv = pD3 rs g pD rg g 6 6 18hv = D2 g(rs rg ) g(rs rg ) â&#x2021;Ľ D2 . v= 18h

(4)

Comparing the above with the equation of a straight line y = mx + c gives a y-intercept of zero and a gradient m = g(rs rg )/18h. Thus h can be found by dividing g(rs rg )/18 by the gradient of the graph of v against D2 . Note that the units of the gradient must be (m/s)/m2 or 1/(s m).

3

Procedure

The material used included a cylinder of glycerol, some steel spheres of varying diameters, an outside micrometer, a stopwatch, some magnets, and some tissue paper. A stand and clamp is used to secure the cylinder in place, with rubber bands used to mark distance intervals. An electronic balance and a measuring boat is used to weigh the spheres. The apparatus setup is shown below.

71

glycerol level

53 cm

rubber band v1

10 cm t1

10 cm

t2

rubber band

v2 rubber band

The independent variable, D, is measured using an outside micrometer. The instrument is chosen for its high precision of Âą0.01 mm. However, surface irregularities of the sphere can increase the actual uncertainty. Generally, since the spheres have diameters on the order of a few millimetres, the uncertainty is less than one part in a hundred. The measurement of D is repeated 5 times, to decrease the effects of errors due to roughness of the spheres. The measurements are within instrumental uncertainty. Note that zero errors must be accounted for when using the instrument, and the fine-adjustment ratchet stop should be used to avoid over-tightening.

The dependent variable, v, is measured indirectly using a stopwatch to find the times taken (t1 and t2 ) for them to descend 10 cm and 20 cm respectively. The eyes of the experimenter must be level with the relevant rubber band to avoid parallax error. These lengths are chosen near the bottom of the cylinder to allow the spheres to reach terminal velocity. The 10 cm intervals each have an uncertainty of Âą0.4 cm. Although the stopwatch is chosen for its high precision of 0.01 s, reaction time differences drastically decrease precision. Since the measurements are on the order of a few seconds, it seems that the uncertainty should be less than 1 %.

However, this is a gross underestimate. At least five stopwatch readings are made GEOLOGY 101 REPORT

72

!1

for each independent D since this is needed to reduce random error. Measurements may be repeated if there are anomalies. The sphere is removed from the cylinder after each repeat by a magnet which attracts it from the outside of the cylinder.

Errors • Systematic – Temperature of the glycerol, kept constant within ±0.5 degrees Celsius with air-conditioning • Random – Reaction time affects the measurement of t1 and t2 – Whether or not the spheres reached terminal velocity – Thickness of the delimiting rubber bands Safety risks are minor. Glycerol is a slight hazard if it contacts the skin, eye, or is ingested as it is an irritant. Exercise due care so that glycerol is not splashed anywhere. Wipe hands with tissue paper or wash hands to minimise risk.

Brief running order 1. Set up apparatus 2. Measure D for each sphere.

3. Drop sphere in the middle of the cylinder 4. Take reading of times with the stopwatch (using relevant buttons) 5. Write down readings for t1 and t2 6. Use magnets to attract the sphere, removing it from the cylinder 7. Clean sphere with tissue paper and reset timer 8. Repeat five times or more if necessary 9. Use a sphere with different diameter 10. Repeat with seven spheres (in the actual experiment, only four was done)

73

4

Results

The data collected on 24 November 2016, the day of the experiment, is presented below. Since the absolute uncertainty of the diameters D are all 0.01 mm, the % uncertainty DD(%) = 100% â&#x2021;Ľ (0.01/D). Multiply this by 2 to get the % uncertainty in D2 . The absolute uncertainty in D2 , |DD2 |, is D2 â&#x2021;Ľ (DD2 (%)/100).

For the full raw data and the derivation of the remaining figures in the table, see Appendix 1.

D (mm) DD(%) 5.02 0.20 3.97 0.25 2.97 0.34 1.48 0.68

D2 (mm2 ) 25.20 15.76 8.82 2.19

DD2 (%) 0.40 0.50 0.67 1.35

|DD2 | 0.10 0.08 0.06 0.03

v (cm/s) 7.61 5.54 3.25 0.90

|Dv| 0.44 0.12 0.04 0.01

Dv(%) 5.72 2.23 1.30 1.09

Legend: uncertainty is denoted by D, absolute uncertainties have | . . . | around them. Note that the absolute uncertainties are plotted on the graph.

The graph is plotted below.

74

5

Analysis

The graph shows that v increases proportionally as D2 increases, with the high R2 value of 0.9933 indicating strong correlation. The y-intercept of 0.4108 cm/s alludes to the existence of systematic errors.

The density of the steel spheres used is 7868 ± 55 kg/m3 , equivalent to an uncertainty of 0.7 %. Refer to Appendix 2 for calculations. The density of glycerol is 1260 kg/m3 at 25 degrees Celsius. Since the experiment is conducted at 22 degrees Celsius, this figure should be quite accurate. In fact, source (2) states that this is correct to three significant figures. The standard acceleration due to gravity, g = 9.81 m/s2 will be used here. As discussed earlier, the viscosity of glycerol is g(rs rg )/18 divided by the gradient. The gradient of the above graph is 0.2921 (cm/s)/mm2 or 2921 /(s m). The maximum and minimum gradients are 3057 and 2506, in the same units (see Appendix 1), respectively. Therefore the percentage uncertainty in the gradient is 100% ⇥ (3057 2506)/2 = 9.43%. g(rs rg ) 18 becomes

9.81 ⇥ (7868 18

1260)

which is 3602 kg/(s2 m2 ).

Dividing yields the viscosity 1.233 Pa s. Ignoring uncertainties in the acceleration of free fall and the density of glycerol, the percentage uncertainty in the viscosity is therefore 9.43 + 0.7 = 10.13% which is 0.125 Pa s. This gives the viscosity measurement 1.23 ± 0.12 Pa s. Assuming a purity of 100%, this agrees with the 1.19 ± 0.05 Pa s figure at 22 ± 0.5 degrees Celsius, determined by interpolation using data by Segue and Oberstar (1). See Appendix 3 for how the interpolation is done.

The usage of Stokes’ law comes with many assumptions. The spheres must be homogenous. There is no way to ensure that this is the case in this experiment.

The spheres must also be smooth, which is part of the reason the data collected using the 12 mm sphere is discarded, since it is rough with a |DD| of ±0.03 mm.

The balancing of upthrust and drag with weight required that the spheres are travelling at terminal velocity. Using the erratic data from a stopwatch, this is difficult to ascertain. Even though the temperature stayed within 22 ± 0.5 degrees Celsius, the viscosity of glycerol can still vary by 0.10 Pa s. (See Appendix 3) In future experiments, experimenters should consider using finer variations of sphere size, to increase the number of independent variables, for a more reliable graph and gradient calculation. They should carry out precautions to make sure that the glycerol stays pure. They should also film the falling process of the 75

spheres to calculate times more accurately, since playing back the video frame by frame is not dependent on human reaction time. The position can be plotted on Tracker to ensure that terminal velocity is reached. Also, a heat regulator (e.g. a hot water bath) can be used to guarantee that the temperature of the glycerol remains constant (to a greater certainty) throughout the experiment. Small bubbles in the glycerol will interfere with the path of the spheres, thus complicating measurements. Therefore, a large cylinder may be desirable since it is then unlikely that two spheres will repeat the exact downwards path.

Even though the h measured here matches the h in published literature, the uncertainty is large. In sum, further experiments are required to close this open case.

6 6.1

Appendices Appendix 1

t1 and t2 are the times taken for the sphere to descend 10 cm and 20 cm respectively. v1 and v2 are its speeds through the first and second 10 cm, respectively. (See ”apparatus” for clarification) The change in velocity is calculated thus: d v(%) = 100% ⇥ (v2 v1 )/v1 . If the velocity changed more than 10% from the first 10 cm to the second 10 cm, then the data is discarded due to unreliability. Also, the large negative d v(%)’s for the 12 mm sphere clearly indicate that terminal velocity is not reached.

The terminal velocity reading, v, for a particular diameter D is calculated by taking the average of the v2 ’s. The absolute uncertainty in v, or |Dv|, is half the range of the v2 values. The percentage uncertainty, Dv(%) is 100% ⇥ (|Dv|/v).

The results are tabulated on the next page.

76

Results t2 (s) 2.71 2.65 2.77 2.69 2.62 2.59 2.65 2.57 3.52 3.51 3.59 3.58 3.52 6.09 6.13 6.07 6.03 6.01 21.47 21.71 21.47 21.63 21.56

v1 (cm/s) 7.58 7.81 7.14 7.25 7.63 7.41 7.30 7.63 5.68 5.85 5.71 5.71 5.81 3.37 3.26 3.30 3.37 3.44 0.95 0.95 0.96 0.96 0.96

v2 (cm/s) 7.19 7.30 7.30 7.63 7.63 8.06 7.81 7.94 5.68 5.56 5.43 5.46 5.56 3.21 3.27 3.29 3.27 3.23 0.91 0.90 0.91 0.89 0.89

d v(%) -5.04 -6.57 2.19 5.34 0.00 8.87 7.03 3.97 0.00 -5.00 -4.89 -4.37 -4.44 -4.81 0.33 -0.33 -2.94 -6.13 -3.93 -4.94 -5.35 -6.70 -7.33

D (mm) t1 (s) t2 (s) 5.02 1.52 2.82 12.02 0.51 1.08 12.02 0.44 0.93 12.02 0.39 0.95

v1 (cm/s) 6.58 19.61 22.73 25.64

v2 (cm/s) 7.69 17.54 20.41 17.86

d v(%) 16.92 -10.53 -10.20 -30.36

D (mm) 5.02 ” ” ” ” ” ” ” 3.97 ” ” ” ” 2.97 ” ” ” ” 1.48 ” ” ” ”

t1 (s) 1.32 1.28 1.40 1.38 1.31 1.35 1.37 1.31 1.76 1.71 1.75 1.75 1.72 2.97 3.07 3.03 2.97 2.91 10.52 10.58 10.44 10.44 10.37

Anomalies

The graphs of maximum and minimum slopes below are used to calculate the uncertainty in the gradient of v against D2 .

77

Maximum slope: gradient = 3067 /(s m)

Minimum slope: gradient = 2506 /(s m)

6.2

Appendix 2

On the next page is the raw data of masses and diameters, allowing the density of the steel spheres to be calculated by rs = ms /D. The average is 7868, and the absolute uncertainty is (7936 7825)/2 = 55, giving rs = 7868 Âą 55 (kg/m3 ).

78

D (mm) 22.20 15.98 5.02 3.97

6.3

ms (g) 45.04 16.72 0.52 0.26

rs (kg/m3 ) 7862 7825 7850 7936

Appendix 3

The graph below shows the glycerol viscosities in centipoises against temperature (source 1). (1000 centipoises = 1 Pa s) The y axis is logarithmic. The data points show that viscosity decreases exponentially with temperature. Interpolating using h(cP) = 7516 ⇥ 10 0.3631T between the data points for 20 and 30 degrees Celsius, the viscosity at 22 ± 0.5 degrees is 1.19 ± 0.05 Pa s.

7

Bibliography 1. Segur, J. B.; Oberstar, H. E. (1951). ”Viscosity of Glycerol and Its Aqueous Solutions”. Industrial & Engineering Chemistry. 43 (9): 2117–2120. doi:10.1021/ie50501a040 2. ”Specific Gravity and Percent Glycerol by Weight.” Physical Properties of Glycerine and Its Solutions. New York: Glycerine Producers’ Association, 1963. 2-3. Print.

1

Year 12 (Churchill) 79

â&#x20AC;&#x2DC;We aim high.

We would like the next Nobel Laureate in Physics from Hong Kong to be an Old Harrovian.â&#x20AC;&#x2122;