Chapter 1: Forces

2.1.0 Forces: Introduction When and how to use these pages The Introduction in the Student Book indicates some of the ideas and skills in this topic area that students will already have met from KS2 or from previous KS3 work, and provides an indication of what they will be studying in this chapter. Ideas you have met before is not intended to comprehensively summarise all of the prior ideas, but rather to point out a few of the key ones and to support the view that scientific understanding is progressive. Even though students might be meeting contexts that are new to them, they can often use existing ideas to start to make sense of them. In this chapter you will find out indicates some of the new ideas that the chapter will introduce. Again, it isn’t a detailed summary of content or even an index page. Its purpose is more to act as a ‘trailer’ and generate some interest. The outcomes, then, will be recognition of prior learning that can be built on, and interest in finding out more. There are a number of ways this can be used. You might, for example:

• Use Ideas you have met before as the basis for a revision lesson as you start the first new topic. • Use Ideas you have met before as the centre of spider diagrams, to which students can add examples, experiments they might have done previously or what they found interesting.

• Make a note of any unfamiliar/difficult terms and return to these in the relevant lessons. • Use In this chapter you will find out to ask students questions such as: • Why is this important? • How could it be used? • What might we be doing in this topic?

Overview of the chapter This chapter develops ideas about forces, building on material from Book 1. The first part explores situations in which forces are in opposition, such as the actions of friction and drag in opposing movement, and then explores Hooke’s Law, developing a more quantitative approach. The second part considers pressure both in relation to solids and fluids, developing explanations around applications such as floating and sinking and using calculations to work out pressure.

Obstacles to learning The students may need extra guidance with the following concepts. Students may think that a non-zero resultant force produces a steady speed: for example, an object sinking at a steady speed does that because there is a constant non-zero downward force acting on it. They may think that whether an object floats or sinks is purely a function of weight – heavier objects sink and lighter objects float

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Chapter 1: Forces

How the Programme of Study is covered by the Student Book Topic

Pressure

Forces

Contact forces

Big idea

Lesson

Programme of study reference

2.1.1 Analysing equilibrium

Opposing forces and equilibrium: weight held by a stretched spring or supported on a compressed surface Using force arrows in diagrams, adding forces in one dimension, balanced and unbalanced forces

2.1.2 What a drag!

Forces associated with rubbing and friction between surfaces, with pushing things out of the way; resistance to the motion of air and water

2.1.3 Understanding stretch and compression

Forces associated with deforming objects Measurements of stretch or compression as force is changed

2.1.4 Investigating Hooke’s Law

Forces associated with deforming objects; stretching and squashing – springs Measurements of stretch or compression as force is changed Force–extension linear relation, Hooke’s Law as a special case

2.1.5 Exploring pressure on a solid surface

Pressure measured by the ratio of force over area – acting normal to any surface

2.1.6 Exploring pressure in a fluid

Pressure in liquids, increasing with depth Atmospheric pressure; decreases with increase of height as the weight of air above decreases with height

2.1.7 Calculating pressure

Pressure measured by the ratio of force over area – acting normal to any surface

How the AQA KS3 Syllabus is covered by the Student Books and Teacher Guide Forces Student Book

Teacher Guide

Know When the resultant force on an object is zero, it is in equilibrium and does not move, or remains at constant speed in a straight line.

1.1

One effect of a force is to change an object’s form, causing it to be stretched or compressed. In some materials, the change is proportional to the force applied.

1.3, 1.4

Skill: Sketch the forces acting on an object, and label their size and direction.

1.1

Equilibrium: State of an object when opposing forces are balanced.

1.1

Deformation: Changing shape due to a force.

1.3

Linear relationship: When two variables are graphed and show a straight line which goes through the origin, and they can be called proportional.

1.4

Newton: Unit for measuring forces (N).

1.1

Resultant force: Single force which can replace all the forces acting on an object and have the same effect.

1.1

Friction: Force opposing motion which is caused by the interaction of surfaces moving over one another. It is called ‘drag’ if one is a fluid.

1.2

Tension: Force extending or pulling apart.

1.3

Compression: Force squashing or pushing together.

1.3

Contact force: One that acts by direct contact.

1.1

Apply Explain whether an object in an unfamiliar situation is in equilibrium.

1.1

Describe factors which affect the size of frictional and drag forces.

1.2

Describe how materials behave as they are stretched or squashed.

1.3, 1.4

Describe what happens to the length of a spring when the force on it changes.

1.3, 1.4

Extend Evaluate how well sports or vehicle technology reduces frictional or drag forces.

1.2

Describe the effects of drag and other forces on falling or accelerating objects as they move.

1.2

Using force and extension data, compare the behaviour of different materials in deformation using the idea of proportionality.

1.3, 1.4

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Chapter 1: Forces

Pressure Student Book

Teacher Guide

Know Pressure acts in a fluid in all directions. It increases with depth due to the increased weight of fluid, and results in an upthrust. Objects sink or float depending on whether the weight of the object is bigger or smaller than the upthrust.

1.6

Different stresses on a solid object can be used to explain observations where objects scratch, sink into or break surfaces.

1.5

Skill: Use the formula: fluid pressure, or stress on a surface = force (N)/area (m2).

1.7

Fluid: A substance with no fixed shape, a gas or a liquid.

(1.6)

Pressure: The ratio of force to surface area, in N/m2, and how it causes stresses in solids.

1.7

Upthrust: The upward force that a liquid or gas exerts on a body floating in it.

1.8

Atmospheric pressure: The pressure caused by the weight of the air above a surface.

1.6

Apply Use diagrams to explain observations of fluids in terms of unequal pressure.

1.6

Explain why objects either sink or float depending upon their weight and the upthrust acting on them.

1.8

Explain observations where the effects of forces are different because of differences in the area over which they apply.

1.5, 1.7

Given unfamiliar situations, use the formula to calculate fluid pressure or stress on a surface.

1.7

Extend Use the idea of pressure changing with depth to explain underwater effects. Carry out calculations involving pressure, force and area in hydraulics, where the effects of applied forces are increased. Use the idea of stress to deduce potential damage to one solid object by another.

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Chapter 1: Forces

2.1.1 Analysing equilibrium Lesson overview Learning objectives • Analyse situations to identify the various forces that are acting. • Explore static situations in which objects are held in equilibrium and the nature of the forces involved. Learning outcomes • Identify relevant forces and their directions. [O1] • Explain how opposing forces can result in an object being in equilibrium. [O2] • Explain how a more complex set of opposing forces can result in an object being in equilibrium. [O3] Skills development • Working scientifically: 2.6 Construct explanations • Developing numeracy: Use units correctly • Developing literacy: Develop explanations taking into account several factors (Q10) Resources needed Equipment and materials as detailed in the Technician’s notes; Worksheet 2.1.1; Practical sheet 2.1.1; Technician’s notes 2.1.1 Common misconceptions No forces are acting if an object is stationary. Key vocabulary contact force, balanced forces, equilibrium, resultant force, newton (N)

Teaching and learning Engage • Show a mass suspended from a newtonmeter. Point out that there is no movement, and ask the students if any forces are acting. They should identify the downward force of weight and the upward force through the newtonmeter. [O1&2]

• Pair talk The students explain what the lack of movement tells them about the forces acting on the newtonmeter. (They are balanced – they are in equilibrium.) [O1&2]

Challenge and develop • The students analyse a simple equilibrium situation, by reading the ‘Balancing Forces’ section in the Student Book and answering questions 3–5. [O1&2]

• Ask the students to draw the force arrows acting on a piece of soft foam that is stationary on a bench and to explain why there is no movement. (The upward force from the bench is in equilibrium with the downward force of the foam’s weight.) They discuss how the force diagram would be different if a large mass were placed on top of the foam. (The bench would provide a bigger upward force, which would be in equilibrium with the combined forces of the foam’s weight and that of the added mass.) [O1&2]

• Pair work The students work in pairs to exert opposite pulling forces on a heavy object on the floor, using newtonmeters. See Technician’s notes 2.1.1 and Practical sheet 2.1.1. The students consider why the two newtonmeters can pull with different forces and yet the object does not move. (The force of friction added to the smaller force balances the larger force.) [O2&3] Higher-attaining students may be able explain why equilibrium can exist for a range of different pulling forces. (Friction opposes movement – so long as the force of friction is not overwhelmed, it will resist any movement.)

Explain • The students consider a variety of equilibrium situations, such as a bulldog clip holding paper, a gymnast balancing on a beam and washing hanging on a line, and explain how the forces balance each other. [O1, 2&3] Higher-attaining students may suggest other situations in which more than two forces are acting and are in equilibrium.

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Chapter 1: Forces

Consolidate and apply • Ask the students to compare the forces acting when a heavy object is on a rigid beam to when the object is on a flexible beam. (They should identify that the forces are the same in both cases.) [O1&2]

• Pairs to fours Ask the students to compare the forces acting when an object is floating in water to when some extra weight is added so that the object sits slightly lower in the water. (The weight and upthrust forces balance in both cases; the forces are higher in the second situation.) [O2&3]

• The students analyse equilibrium through the tasks of Worksheet 2.1.1. [O1, 2&3]

Extend • Ask students able to progress further to draw diagrams, with force arrows to scale, to show the forces acting in more complex equilibriums, for example those in task 3 of Worksheet 2.1.1. They will need to show care and resilience to succeed with the scale diagrams. [O3]

Plenary suggestions The big ideas Ask the students to write down three ideas that they have learned during the lesson. Then ask them to share their facts in a group and to compile a master list of facts, with the most important at the top. Ask for ideas to be shared to find out whether groups agreed or not. [O1, 2&3]

Answers to Student Book questions 1. 2. 3. 4.

Pulling force. Gravity. Downward force of weight; upward force provided by the spring. Diagram a): weight arrow acting downwards; equal and opposite force provided by the spring. Diagram b): as for diagram a) but both arrows should be larger. 5. The forces balance; they are in equilibrium. 6. Stays the same. 7. Gravity is acting downwards; air resistance is equal and opposite. Students may comment that air resistance is lower initially. 8. Because the forces acting on it become balanced; and are in equilibrium. 9. A large force arrow shows pushing from the left; two smaller force arrows – pushing force and friction – are acting in the opposite direction. Higher-attaining students should draw the arrows to scale to show that they balance. 10. The effect of the force of friction is reduced, so she would accelerate.

Answers to Worksheet 2.1.1 1. a) All the forces acting on an object balance one another. b) i) The downward force of the person’s weight; the equal and opposite upward force from the mattress springs. ii) The downward force of the person’s weight; the equal and opposite upward force from the scales. iii) The downward force of the coat and hanger’s weight; the equal and opposite upward force from what the hanger is attached to. 2. a) The downward force of the weight of the person; the equal and opposite upward force from the beam; the downward force of the weight of the beam; the upward forces from the supports at either end of the beam; balancing the weight of the beam and the person. b) There would be a larger downward force of the weight of the person; also larger downward forces exerted on the supports of the beam; but larger upward forces to balance the extra weight. 3. a) The forces of air resistance and friction are in equilibrium with the pushing force from the engine. b) Friction from the tyres and/or the force through the steering wheel, to balance the pushing force of the wind. c) There is a large sideways force caused by air resistance against the side of the vehicle. It could cause the vehicle to swerve off course or to be blown over.

Answers to Practical sheet 2.1.1 1. Friction between the box and the floor. 2. The arrow for the friction force is in the opposite direction to the pulling force and is the same size. 3. The first pulling force is now greater than the friction force, but there is a pulling force backwards, of length equal to the difference between the forward pulling force and the friction. 4. The forces are balanced: the total forward force is equal to the total backward force. Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces

2.1.2 What a drag! Lesson overview Learning objectives • Describe the effects of drag and other forces on objects as they move. • Describe factors that affect the size of frictional and drag forces. • Evaluate how well sports or vehicle technology reduces frictional or drag forces.

Learning outcomes • Explain how the streamlining of an object alters the drag. [O1] • Explain why drag is sometimes a nuisance but sometimes useful. [O2] • Identify ways in which the amount of drag can be controlled. [O3]

Skills development • Working scientifically: 2.6 Construct explanations • Developing numeracy: Gather data • Developing literacy: Evaluate the benefits of natural and artificialdesigns Resources needed Tall transparent container of water; modelling clay; scales; Worksheet 2.1.2 Common misconceptions Students may think that heavier objects always fall faster, that Key vocabulary friction, drag, streamlining

Teaching and learning Engage • Show students pictures of situations in which an object or animal is streamlined, and ask them to identify key features of the shape and suggest why they are there. [O1]

• Show the students picture of objects in which drag has been maximised; ask them to describe features of the shape and suggest why they are there. [O2]

Challenge and develop • Ask the students to explain what they think is meant by air resistance or water resistance. Draw out ideas about flow and how movement through a fluid can be resisted. Establish ideas about a fluid flowing over an object either easily or with more difficulty. [O1]

• Use force arrow diagrams to summarise the effects of forces opposing motion; show that greater drag means a greater opposing force. [O1 & 2]

Explain • Show the students the example of an aircraft wing and how its shape is changed when the aircraft is coming in to land. Ask students to explain how this affects drag and the balance of forces. [O1 & 3]

• Ask the students to explain how altering the size of the drag force explains other situations, such as a parachute slowing down a car involved in a high-speed run or a person descending by parachute. [O1 & 3]

Consolidate and apply • Set up column of water, and ask the students to design the shape of an object that will descend through water as quickly as possible. Give each group of students the same mass of modelling clay, and ask them to time its descent. [O1, 2 & 3]

• Now repeat the activity but explain that the objective is to design a shape that will descend as slowly as possible. [O1, 2 & 3] Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces

• Look at successful designs from both activities, and ask the students to suggest why they worked well. [O3]

Extend • Ask the students to explain why streamlining is more important for a sports car than for a commercial vehicle. [O1 & 2]

• Ask the students to find out what is meant by drag coefficient and what it indicates. [O3]

Plenary suggestions Ask the students to explain in their own words what is meant by these terms: fluid, drag, air resistance, water resistance, streamlining. [O1, 2 & 3] Ask students to come up with three examples (other than those used in the lesson) of objects that are streamlined and three that are not. [O1, 2 & 3]

Answers to Student Book questions 1. It reduces the air resistance and therefore the energy used in moving. 2. Smooth shape, not having a large vertical front area, not having parts sticking out that will resist the flow of air, such as handles and mirrors. 3. Pointed bow, smooth shape, cuts through water. 4. Flaps are lowered to increase drag and raised to reduce it. 5. It increases the drag. 6. Friction is mainly used where one solid is moving over another, and drag is where a fluid is moving over a solid. 7. The rider is bent over the handlebars to reduce air resistance. 8. The clothing is very smooth and the helmet is shaped and fitted so that air can flow over it easily. 9 a) The higher seat makes it easier to keep your head down and reduce resistance. b) Gears mean more friction in the mechanism and also affect the streamlining.

Answers to Worksheet 2.1.2 1.

a) to increase speed b) to increase speed and reduce fuel needed to complete journey c) to reduce energy needed to travel through water and to allow acceleration and high speed to catch prey. d) to increase speed and reduce energy needed to travel.

2.

a) various solutions are possible but generally a streamlined shape is required. b) various solutions are possible but ones that increase drag by having features that prevent water flowing smoothly will be successful. Such features should be labelled.

3.

a) close fitting, smooth, light, streamlining body shape b) crouching down – to reduce air resistance. c) at slower speeds the air is likely to be moving more slowly over the body so air resistance is less of an issue – there’s less drag to deal with. At high speeds air needs to flow quickly over the body so streamlining will make more of a difference.

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Chapter 1: Forces

2.1.3 Understanding stretch and compression Lesson overview Learning objectives • Explain the relationship between an applied force and the change of shape of an object. • Investigate the forces involved in compressing and stretching materials. • Identify applications for compressible and stretchable materials.

Learning outcomes • State that applying a force can compress or stretch an object, and state that the bigger the force the larger the deformation. [O1]

• Use the understanding of forces changing an object’s shape to consider the quality of evidence when investigating change in shape. [O2]

• Explain how forces can cause an object to deform, link the deformation to the size of the force, and recognise

that for a range of forces the amount of deformation is linear and that this can be used to design machines for measuring forces. [O3]

Skills development • Working scientifically: 2.4 Present data • Developing numeracy: Construct and interpret line graphs • Developing literacy: Use key scientific terminology to develop explanations Resources needed Materials and equipment as detailed in the Technician’s notes; graph paper; Worksheet 2.1.3; Practical sheet 2.1.3; Technician’s notes 2.1.3 Common misconceptions: Elastic behaviour refers only to stretching and does not include compressing or returning to the original shape. Key vocabulary deformation, compression, tension

Teaching and learning Engage • Perform some demonstrations (see Technician’s notes 2.1.3 for details, including safety precautions) that allow the students to compare and contrast the behaviour of an elastic material, a ductile material and a brittle material when a force is applied. If possible, show the students a video of elastic behaviour being tested. [O1]

Challenge and develop • The students consider the choice of foam for soft furniture and identify questions they would need to know the answer to in order to choose an appropriate foam. [O1]

• The students investigate how the size of the force applied affects the compression of foam. A board is placed on top of a piece of foam to distribute force evenly, and masses are placed on top. Practical sheet 2.1.3 can be used to guide students’ practical work and analysis of results. The students state the relationship between the force applied and the amount of compression. Worksheet 2.1.3 reinforces the data handling or can be used with the students’ own data. [O1, 2&3] Higher-attaining students might independently see the need for repeats and take steps to avoid problems relating to the foam compressing unevenly.

• The students can compare how much different types of foam compress. They should add masses until the foam is fully compressed, to illustrate the importance of density. [O1, 2&3]

• Ask the students to evaluate the quality of their data and suggest how it could be improved (such as carrying out repeats, or using a more accurate method for measuring thickness). [O2]

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Chapter 1: Forces

Explain • Group talk The students should link the concept of balanced forces to stretching and compression. At equilibrium, the forces of weight and restoring elastic force are balanced. When more force is added, the foam compresses more and the restoring force increases until it balances. [O1&3]

• The students explain the application to weighing machines and share explanations with other groups. [O3]

Consolidate and apply • The students plot and analyse a line graph (see Student Book questions 5 and 6 or Worksheet 2.1.3). [O1&3]

• The students apply the findings from their investigation to the choice of foam in furniture (too rigid – it does not adjust its shape to the person; too soft – it fully compresses, and so gives little additional comfort). [O3] Higher-attaining students could explain the effects as the foam approaches full compression and how this affects comfort.

Extend • Students able to progress further can use the results to suggest how a cushion on the base of a settee could be constructed for people of a wide range of body weights to be supported in comfort. (Use a greater thickness of foam; use two or more foams of different compressibility.) [O3]

Plenary suggestions The big ideas Ask the students to write down three things that they have learned during the lesson. Then ask them to share their facts in a group and to compile a master list of facts, with the most important at the top. Ask for ideas to be shared to find out whether groups agree or not. [O1, 2&3]

Answers to Student Book questions 1. 2. 3. 4. 5. 6.

7.

8. 9.

Foam, metal springs, carbon fibre, climbing ropes, rubber balls, gases. Liquids. Glass, china, some plastics. Scales labelled including units; scales chosen so that the data fills at least half the available space; points marked accurately in fine pencil; smooth line/curve through points (or line of best fit); title. Line graph correctly plotted; the greater the force applied to the spring, the more it is compressed; each additional 10 N gives 3.1 cm of additional compression; except for the last reading. a) Up to 50 N the spring compresses by 3.1 cm for every 10 N added; with 60 N it only compresses a little extra (0.6 cm). b) The spring has become fully compressed. a) It might compress fully with the applied force, and so would offer little comfort or support. b) The applied force might not compress it at all, and so it would be little more comfortable than the wood or other hard material of the chair. Springs stretch or compress in uniform amounts whenever a certain weight is added (the idea of proportionality). The sudden shock of being stopped by a rope with no stretch could injure the climber or snap the rope.

Answers to Worksheet 2.1.3 1. a) Use of a fine pencil; accurate marking of points; labelled axes with units; smooth curve drawn through the points. b) Suitable rules based on (a). 2. a) The greater the force applied, the thinner the foam becomes. Beyond a force of a certain size, the cushion does not become any thinner. b) 1000 N (or slightly less). c) i) It would be suitable for the base of a chair for all but the largest of adults because it would not be fully compressed by their weight. ii) It would be suitable for the back of a chair because it compresses only a few cm when smaller forces are applied. 3. The progressive crumpling of a bumper allows the car and passengers to slow down over a finite distance rather than coming to a sudden halt that would result in more injuries.

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Chapter 1: Forces

2.1.4 Investigating Hooke’s Law Lesson overview Learning objectives • Investigate the effects of applied forces on springs. • Generate data to produce a graph and analyse outcomes.

Learning outcomes • Carry out an investigation into springs and gather data to show simply the relationship between load and extension. [O1]

• Students to use their own data to state Hooke’s Law and explain the elastic limit of a material. [O2] • Obtain a precise set of data by investigation, produce accurately drawn graphs to illustrate Hooke’s Law, and explain the behaviour of a material at the elastic limit. [O3]

Skills development • Working scientifically: 2.1 Analyse patterns • Developing numeracy: Construct and interpret graphs • Developing literacy: Develop explanations from observations and peer assess other explanations Resources needed Equipment as detailed in the Technician’s notes; Worksheet 2.1.4; Practical sheet 2.1.4; Technician’s notes 2.1.4 Key vocabulary extension, Hooke’s Law, elastic limit, linear relationship, extension

Teaching and learning Engage • Raise the students’ curiosity by having three stands and clamps, each supporting a spring and a different hanging mass. Give the students a minute to make observations and consider questions they could investigate. [O1]

• Identify the three main questions this lesson will investigate: • Does a spring stretch by regular amounts as more load is suspended from it? • What is the elastic limit for a spring? • What happens to a spring when its limit is reached? [O2&3]

• Ask the students to recall from the previous lesson what is meant by ‘elastic behaviour’. [O1, 2&3]

Challenge and develop • Demonstrate the apparatus and procedure for investigating the extension of a spring when masses are hung from it. For ease and accuracy, clamp the metre rule alongside the spring with the zero mark aligned with the pointer label (see Practical sheet 2.1.4). Instruct the students to remove the hanging weight before increasing the load, to check that the spring is undamaged and still shows elastic behaviour. [O1, 2&3]

• The students record their observations on Practical sheet 2.1.4 from their own experiment, or from the teacher demonstration, of the outcome of adding masses until the spring is permanently deformed. [O2&3]

• The students present their data in the form of a line graph. [O1, 2&3] Higher-attaining students may realise earlier, through careful observation, when the elastic limit is reached.

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Chapter 1: Forces

Explain • The students state and explain the relationship between the load on the spring and its extension. [O2] • The students work in their practical groups to explain how they can tell when the elastic limit is exceeded. [O2&3] Higher-attaining students may be able to quantify the relationship between force and extension.

Consolidate and apply • Select some students to present their statements and explanations of Hooke’s Law. [O2&3] • Students can complete Worksheet 2.1.4 to reinforce ideas about the elastic limit, the relative size of forces and Hooke’s Law. [O2&3]

• Pair talk/pairs to fours The students suggest two good features of the statement/explanation that was presented and one for improvement, for example two WWWs (What Went Well…) and one EBI (Even Better If…). [O2&3]

• Ask the students to identify the key features of a good graph – they may have listed these in tackling question 4 of the previous lesson. [O3]

Extend For students able to progress further:

• Ask them to consider the reliability of the data they have collected – how they could judge its reliability, and how they might improve its reliability. (They should carry out repeats: when results are reliable, repeated observations are the same or close to the original readings.) [O3]

• Introduce the vocabulary for describing a relationship when a graph is a straight line through the origin: that is, directly proportional. Note: materials may stop deforming proportionally before the elastic limit. [O2&3]

Plenary suggestions Exit slips Each student describes one situation in which knowing about elastic limits is important, and writes it on an ‘exit slip’, which they have to hand in before leaving. These could be reviewed at the start of the next lesson, depending on how well the concept has been understood. [O1, 2&3]

Answers to Student Book questions 1. Newtonmeter (forcemeter), car or bike suspension, mechanical toys, bathroom scales, curly electrical lead, door closer. 2. The elastic material will return to its original shape after a force has deformed it; it easy to manufacture into the required shape; does not break easily; does not corrode. 3. a) 6 cm b) 21 cm c) 0.6 cm. 4. Words to the effect of ‘the extension of a spring is directly proportional to the force applied to it’. 5. As the force increases, the spring extends more. The extension increases by regular amounts (there is a directly proportional relationship) until a certain force is exceeded. Then the spring extends much more with an increase of force, until it breaks. 6. a) 5 N b) 5 cm. 7. a) Between about 8 N and 8.5 N (The elastic limit may be slightly beyond the linear region.) b) You can only tell by checking if the spring returns to its original length.

Answers to Worksheet 2.1.4 1. a) i) As the spring unwinds it makes the toy move; it can be used again and again. ii) The rope absorbs more of the shock of a fall than a non-elastic rope would. iii) It makes the costume tight fitting but still allows the person to move. b) i) The spring would break (or stretch), meaning that the toy would not work (so well). ii) The rope could be weakened and may snap more easily in the future. iii) The material could rip or be left permanently stretched. 2. a) Suggested order: vii), v), i), viii), vi), iii), ii), iv). 3. Elastic behaviour, so can be used many times; predictable, linear extension or compression makes calibration and reading straightforward. Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces

2.1.5 Exploring pressure on a solid surface Lesson overview Learning objectives • Explain how pressure can be applied to a solid surface. • Describe some effects of varying pressure.

Learning outcomes • Describe the effects of varying pressure on a solid surface and suggest factors that affect this. [O1] • Explain how the pressure on a solid surface may vary and the effects that this has. [O2] • Analyse situations in which factors have been changed to alter the pressure applied. [O3]

Skills development • Working scientifically: 2.6 Construct explanations • Developing numeracy: Understand surface area • Developing literacy: Describe relationships between factors and link these to observations Resources needed Wine bottle corks; steel pins; drawing pins; coloured strips of paper (two colours, one of each per student); Worksheet 2.1.5a (copied onto card); Worksheet 2.1.5b Common misconceptions Force and pressure are the same. Key vocabulary pressure, area

Teaching and learning Engage • Ask the students to make predictions about pressure: for example, ‘Will an elephant do more or less damage to a wooden floor than a woman in stiletto heels?’ (An elephant weighs about 5000 kg and a woman 2 about 50 kg. An elephant’s foot is about 40 cm in diameter with an area of about 1200 cm ; the area of a 2 stiletto heel is less than 1 cm .) [O1&2] Higher-attaining students should be able to bring in the quantitative idea of surface area.

Challenge and develop • Ask the students to imagine the forces needed to cut modelling clay, first using a ruler and then using a knife. Relate ‘sharpness’ to the degree of pressure. [O1&2]

• The students analyse the effect of pressing a drawing pin into a wine bottle cork (or similar) compared with an ordinary steel pin. (Make it clear that you expect sensible behaviour here.) Elicit that with the drawing pin the force at both ends is the same, but that the pressure is very much different. [O1&2]

• Present the students with a range of situations in which high pressure is desirable or low pressure is desirable – the students sort them by pressure value. For example: • ice skates, nails, scissor blades, hole punch (high pressure desirable) • skis, caterpillar tracks on a digger, multiple broad pillars on a bridge (low pressure desirable). [O1&2]

• Based on the previous activity, the students discuss the reasons why and how pressure is either reduced or increased. The students can answer questions 1 to 6 in the Student Book. Worksheet 2.1.5b also supports the students’ learning here. [O3] Higher-attaining students may be able to suggest and explain their own examples of reducing and increasing pressure.

Explain • Pairs to fours The students explain how pressure varies between a sledge with runners compared with one with a large, flat base and how well each works on different textures of snow. The students consider the quality of evidence that they would need to test their explanations. [O1, 2&3] Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces Higher-attaining students may be able to appreciate that pressure causes ice or snow to melt under a sledge runner, which provides lubrication and reduces friction.

Consolidate and apply • Give pairs of students a shuffled set of the cards from Worksheet 2.1.5a, and ask them to match up the stems and ends of sentences about high and low pressure. [O1&2] Higher-attaining students may be able to produce their own sentence ends and also their own statements about pressure without scaffolding.

Extend • The students can answer questions 7–9 in the Student Book. [O3] • Present students with the context of heavy furniture with small metal castors being stood on a floor. Challenge them to suggest why putting larger discs under the wheels would reduce the stress on the floor. [O3]

Plenary suggestions Heads and tails Each student writes a question about pressure on a coloured-paper strip and the answer on a different coloured strip. In groups of six to eight, each student gets a question and an answer at random. One student reads out their question – the student holding the answer then reads it out, followed by reading out their question. [O1, 2&3]

Answers to Student Book questions 1. 2. 3. 4. 5. 6. 7. 8. 9.

Newton (N). … smaller the pressure. There is very high pressure at the point of the pin. The feet have a large surface area, so the pressure due to the camel’s weight is reduced; this helps stop the camel sinking in the sand. A sharp blade directs the force through a smaller area than a blunt one; the higher pressure cuts more easily. Wheels have a larger contact area than a blade, and so exert less pressure; there would be very low friction, so the roller skates would slip, and steering and stopping would be difficult. Narrow racing skis exert a higher pressure and would sink into soft snow; the wider powder skis would exert a low pressure on hard icy snow and would be hard to control. Longer handles, acting as levers, would produce a bigger force; a narrower cutting blade would concentrate the force onto a smaller area, and the higher pressure would cut the tin lid more easily. Annotated diagrams should show wide padded straps to reduce the pressure on the shoulders, and a waist belt to spread the weight further.

Answers to Worksheet 2.1.5a a) With ii b) With v c) With i d) With iii e) With iv.

Answers to Worksheet 2.1.5b 1. a) True b) True c) False d) True e) False. 2. E, B, C, A, D. 3. a) The large area reduces the pressure on the ground, and also of the reaction force on the foot; this is needed because of the huge weight (force). b) The large number of small teeth provides high pressure at the point of each tooth; this helps the saw cut through the material. c) The pointed teeth create high pressure, which helps the teeth to penetrate the prey. d) The caterpillar tracks cover a much larger area than wheels, and so the pressure on the ground of the large weight of the vehicle is reduced; this helps to stop the tank sinking into the ground and getting stuck.

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Chapter 1: Forces

2.1.6 Exploring pressure in a fluid Lesson overview Learning objectives • Describe how pressure in a liquid alters with depth. • Describe how pressure in a gas varies with height above the Earth. • Explain pressure changes in relation to particles and gravity.

Learning outcomes • Describe how pressure increases with depth in a fluid, and some effects of this. [O1] • Explain why pressure increases with depth in a fluid. [O2] • Identify implications of differing atmospheric pressure at different heights and across the world. [O3]

Skills development • Working scientifically: 2.6 Construct explanations • Developing numeracy: Construct graphs • Developing literacy: Use sentence stems to link scientific ideas and evidence Resources needed Equipment and materials as detailed in Technician’s notes; Worksheet 2.1.6; Technician’s notes 2.1.6 Common misconceptions Wind flows from high- to low-pressure systems. Key vocabulary atmospheric pressure, depth, height, fluid

Teaching and learning Engage • Show the students a can with three holes in its side at different heights. Before they see the Student Book, ask them to predict the outcome of filling the can with water. [O1&2]

• Ask the students to attempt to explain why the water squirts furthest from the lowest hole. [O1&2] Higher-attaining students may realise that it has to do with water pressure varying with depth.

Challenge and develop • The students predict what will happen when a plastic bag full of water is punctured in several places at the same height with a knitting needle – demonstrate this. (The water flows from all the holes showing that pressure does not depend on direction.) [O2]

• The students predict and explain what would happen if a beaker covered in an elastic membrane were to be submerged in deep water – demonstrate this. (Regardless of orientation, the membrane will bulge inwards due to the water pressure.) [O2]

• The students can do tasks 1 and 2 of Worksheet 2.1.6. In task 2 they present evidence in the form of a graph showing how pressure varies with depth. [O1&2]

• Ask the students to suggest how the graph could inform the design of a submarine. [O3]

Explain • Show the students a U tube partially filled with water. They compare the levels in the two sides and try to explain what they see in terms of particles and gravity. Ask them further to explain why, when water is poured into one arm, the levels equalise again. [O2&3] Higher-attaining students may be able to appreciate that atmospheric pressure is also acting but is the same on both sides.

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Chapter 1: Forces

• Pair talk The students collaborate to discuss the pressure that a diver experiences in a tall, narrow tank of water compared with a swimming pool of the same depth. (Pressure is the same in both cases because the number of particles of water in a column above the diver is the same.) [O2&3]

Consolidate and apply • The students can do questions 1–5 in the Student Book. [O1, 2&3] • Remind the students of how water pressure varies with depth, and ask them to use this to explain the variation of air pressure with height. (Air particles have weight because gravity is pulling them. The higher you are, the fewer air particles there are to press down on you.) [O2]

• Discuss why mountaineers experience difficulty in breathing. (The higher the altitude, the lower the air pressure, so fewer oxygen molecules are available.) [O3]

• Pair talk/Pairs to fours The students explain (verbally, in writing and using diagrams) what would happen to a balloon partially inflated at sea level and then released to a high altitude. [O1, 2&3] Higher-attaining students should be challenged to explain what would happen to the balloon if it were taken under water or warmed up in relation to its surroundings.

• ‘I think that is… because…’ The students watch a demonstration of a partially inflated balloon in a bell jar being evacuated using a vacuum pump (see Technician’s notes 2.1.6). They then write their own explanation. [O2&3] Lower-attaining students could be provided with various explanations to select from.

Extend Ask students able to progress further to:

• read the ‘Explaining pressure in the atmosphere’ section of the Student Book and answer questions 6–8 [O3] • do task 3 of Worksheet 2.1.6 [O3] • explain why a syringe with a narrow opening will squirt further than one with a wide opening (the force is acting through a smaller area when the opening is narrow, therefore the pressure is higher) [O3]

• find out about the challenges presented by high-altitude balloon flight. [O3] • consider implications for the design of submarines of pressure increasing with depth and explain why they can’t descend to more than a certain depth. [O2]

Plenary suggestions ‘I think that is… because…’ Challenge students to provide explanations for why:

• a dam wall is wider at the base than at the top • a sealed pop bottle full of air will gradually collapse when it is taken down into deep water, and then will expand to its original size when it is brought back up again. [O1, 2&3]

Answers to Student Book questions 1. There is more water above you pressing down. 2. a) The pressure could crush their bodies and damage lungs, bones, etc. b) A whale’s body is flexible; the ribs are joined by very flexible cartilage, and so can be compressed without damage. 3. There are more particles above B compared with A. 4. The particles in a liquid behave in a similar way to the marbles; they are both closely packed, touching and cannot be compressed; when pressure is applied to either, it is transferred throughout the particles/marbles. 5. The marbles do not move/flow as freely as water particles; pressure is not distributed so evenly. 6. The weight of gas particles pulled towards the Earth by gravity. 7. Gas particles are attracted to massive objects in space because of gravity, so between the massive objects there are few particles. 8. Answer – two diagrams showing particles arranged so as to be spaced out and moving in all directions but in the second diagram (25km) they will be more spaced out.

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Chapter 1: Forces

Answers to Worksheet 2.1.6 1. a) lower b) squash/compress c) withstand high pressure d) The pressure drops and their bodies expand and rupture. 2. a) Check for: appropriate scales, labels, accurate points, straight line. b) 1000. c) It makes the numbers easier to manage. d) Pressure is proportional to depth. e) Cannot confidently agree; the student may be correct but it is a much higher pressure than the data we have, so there is a chance that the relationship does not remain the same. 3. Good points are in bold; suggested additions/alterations are italicised. The pressure in a liquid depends on how deep it is. The closer to the surface you are, the lower the pressure. When you are in deep water, the column of water above you presses down to create pressure. Divers cannot avoid the pressure of the column of water on their ear drums by ensuring their ears do not point towards the surface. The pressure in a liquid acts in all directions. Pressure has a variety of different effects. If a dam in a reservoir leaks near its base, the water will flow out much more quickly than if the leak were near the surface. Submarines have to be very strong to withstand the pressure in the deep oceans. The huge weight of water particles above the submarine causes very high pressure, which presses on the submarine from all directions.

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Chapter 1: Forces

2.1.7 Calculating pressure Lesson overview Learning objectives • Identify the factors that determine the amount of pressure on a solid. • Calculate the amount of pressure exerted.

Learning outcomes • Describe the factors that affect the pressure applied to a solid. [O1] • Calculate the pressure applied from the force and the area. [O2] • Explain how the force and area can be varied to alter the pressure applied. [O3]

Skills development • Working scientifically: 2.1 Analsye patters • Developing numeracy: Use formulae to perform calculations and understand units • Developing literacy: Describe in words the relationships shown in formulae Resources needed Equipment and materials as detailed in the Technician’s notes; calculators; Worksheet 2.1.7; Practical sheet 2.1.7; Technician’s notes 2.1.7 Key vocabulary pascal (Pa)

Teaching and learning Engage • Ask pairs of students to compare the pressure exerted on modelling clay by two wooden blocks with masses on top – one block should have twice the surface area of the other. The students should see that, when the force on the larger block is twice that on the smaller block, the depth of the indent is the same in each case. They should attempt to explain this. [O1] Higher-attaining students may make quantitative links between force, area and pressure.

Challenge and develop • Ask the students to complete the statements: • As force increases, pressure… (increases) • As area increases, pressure… (decreases) Then ask them to suggest which of these formulas is correct: pressure = force ÷ area

or

pressure = force × area 2

Then ask them to suggest the units that pressure is measured in, given that force is in N and area is m . 2 (1 N/m = 1 pascal, Pa.) [O1, 2&3] Higher-attaining students may be aware of other commonly used units for pressure – bars, psi.

• The students should calculate pressures in a range of examples such as those in the ‘Example calculations’ section of the Student Book and task 1 of Worksheet 2.1.7. [O2]

• The students collaborate in pairs to investigate how pressure affects how far a block sinks into sand when different forces are applied (Practical sheet 2.1.7). [O2]

Explain • The students analyse their data and use it to describe and explain the relationship between force, area and pressure and how far the block sinks into sand. [O1, 2&3]

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Chapter 1: Forces

Consolidate and apply • Pair work The students work in pairs to write questions that require pressure calculations. After working out the answer to their own questions, they share questions with other pairs. [O2] Higher-attaining pairs could be grouped together so that they can challenge one another more effectively.

• The students could calculate the pressure they exert on the floor. The area of a foot can be estimated by drawing round it on squared paper. [O2]

• The students can then do tasks 2 and 3 of Worksheet 2.1.7. [O2&3]

Extend • Students able to progress further should explain, using their own estimates for force and area in pressure calculations, how the pressure exerted by an army tank caterpillar track compares with that of the tyres of a family car (a typical caterpillar track is 5 m long and 0.5 m wide, and a tank weighs about 500 000 N; a typical 2 contact area for a car tyre is 0.3 m , a typical weight of a car is 15 000 N). [O2&3]

Plenary suggestions The big ideas The students write down three ideas that they have learned about pressure. They then share their facts in groups and compile a master list with the most important at the top. Ask for ideas to be shared and find out which group(s) agreed. [O1, 2&3]

Answers to Student Book questions 1. 2. 3. 4. 5. 6. 7. 8.

2

Pascal (Pa); N/m . P = F ÷ A. 2 N/cm . 10 Pa. 125 Pa. Pressures are 20 Pa and 40 Pa, respectively; the second crate exerts the greater pressure. 2 0.5 m . a) The pressure is higher when the person is standing; the area of the feet is smaller than the area of the bottom and legs when sitting. (Higher-attaining students may realise that the force is not applied equally over the contact area, so the situation is actually more complex.) b) Estimate the contact area in both cases by drawing the outline on squared paper; measure the weight of the person in newtons; use the pressure formula. c) The force is higher when you bounce, so the pressure increases.

Answers to Worksheet 2.1.7 2

2

2

1. a) A: 12 m ; B: 8 m ; C: 6 m . b) i) 1.25 Pa ii) 1.67 Pa (to 3 significant figures) iii) 0.83 Pa. 2. a) 20 000 Pa; 25 000 Pa. b) 1200 N; 200 N. 3. a) Any reasonable ideas; minimum of four contact points. b) Need to know the combined weight of the rack and load; measure the total contact area of the mounting points for the rack; use the formula P = F ÷ A. c) Fit more contact points; or ones with a larger combined area. d) i) The pressure that the roof can withstand; the maximum total force that the car body can support without damage; a sensible safety margin to allow for bumpy roads and misuse of the rack. ii) People may overload the rack; the rack may weaken with age; bumpy roads will lead to greater force and pressure.

Answers to Practical sheet 2.1.7 1–3. The students’ own answers. 4. Pressure causes objects to sink in sand. When the pressure becomes too large, the sand might not support the object. 5. Choose more solid ground or build wide, strong foundations to reduce the pressure. 6. Pertinent comments relating to whether reported figures are close to true value, e.g. how well the depth of the indent can be measured and ways of improving, such as thinking about where the depression is measured from.

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Chapter 1: Forces

2.1.8 Explaining sinking and floating Lesson overview Learning objectives • Explain why some objects float and others sink. • Relate floating and sinking to density, displacement and upthrust. • Explain the implications of these ideas.

Learning outcomes • Suggest why some objects float and others sink. [O1] • Explain why some objects float and others sink using concepts of density, displacement and upthrust. [O2] • Apply ideas of density and displacement to predict the outcome of various situations. [O3]

Skills development • Working scientifically: 2.9 Collect data • Developing numeracy: Make careful measurements, using appropriate units • Developing literacy: Translate information from diagrams into written explanations Resources needed Equipment and materials as detailed in the Technician’s notes; Worksheet 2.1.8; Practical sheet 2.1.8; Technician’s notes 2.1.8 Key vocabulary density, buoyancy, upthrust, displaced

Teaching and learning Engage • Check the students’ understanding of density from earlier work by asking them to explain why steel and wooden blocks of equal volume have different weights, and why wood floats but steel sinks. [O1&2]

• Suspend a piece of wood from a forcemeter, and note its weight. Identify the students’ prior knowledge by asking them to predict how the forcemeter reading will change when the wood is lowered slowly into water. Repeat with an object that sinks. [O2] Higher-attaining students may notice that water is displaced.

Challenge and develop • Ask the students to push a tennis ball or a block of wood into a bowl of water to feel the upwards pushing force (upthrust). Then ask them to explore the existence of upthrust on objects that sink, by repeating with a block of aluminium. [O2]

• The students can then investigate the readings on a forcemeter and top-pan balance as they lower blocks of different materials into water. They can use Practical sheet 2.1.8 to guide their method and subsequent data analysis. They will be required to act responsibly for this activity to be successful. [O2]

• The students should also measure the volume of water displaced when a block is lowered into water. They then relate the weight of water displaced to the size of the upthrust measured. [O2]

• Return to the discussion of why wood floats and aluminium sinks, asking the students to suggest explanations using the terms ‘density’, ‘displacement’ and ‘upthrust’. [O1&2]

• Ask the students to explain the evidence that the upthrust is the same for steel and aluminium blocks (of the same size) when submerged in water. (Archimedes’ principle: upthrust = weight of fluid displaced.) [O2]

Explain • Ask the students, working individually, to explain floating and sinking in relation to density, using diagrams and text. [O1&2] Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces

• Pairs to fours Working in pairs the students produce an explanation of how a boat made of steel floats. Then they join with another pair to check agreement and refine their explanation. Take feedback. [O3]

Consolidate and apply • Use the Student Book questions for consolidation. [O1, 2&3] • The students suggest why a can of diet cola floats in water whereas a can of standard cola sinks. (The density of standard cola is higher because of dissolved sugar.) [O1, 2&3] Higher-attaining students could draw particle diagrams to explain the difference between the two types of cola.

• Ask the students to apply the idea of average density to explain why the shape and the total mass of a steel ship are important. [O3]

Extend • Ask students able to progress further to predict, investigate and explain the effect of upthrust with a denser liquid than water such as strong saline solution. [O3]

Plenary suggestions ‘I think that is… because…’ Show the students four boiling tubes, sealed with bungs – one is full of water; one is half full of water; one is full of strong saline; one is half full of water with some lead shot added. The students predict whether each will float or sink, and explain why. Alternatively, task 3 of Worksheet 2.1.8 may be used. [O1, 2&3]

Answers to Student Book questions 1. 2. 3. 4. 5.

For example: stone, copper and pottery sink; wood, cork and expanded polystyrene float. They are no longer supported by the upthrust of the water. The particles are more massive and/or are more tightly packed. How large the upthrust force is: 7 – 4 = 3 N. a) The wood is less dense than water. b) The water provides upthrust, which partially supports the weight of the steel. c) The object displaces water equivalent to its own volume. d) The boat is buoyant because it displaces a large volume of water, which gives a large upthrust. 6. a) Equal sized upward and downward arrows. b) Equal sized upward and downward arrows, bigger than in (a). c) Two downward-acting arrows (weight and the downward push) balanced by a large upthrust arrow. d) Small downward arrow (weight) and large upthrust arrow. 7. The weight of the boat would increase and it would sit lower in the water; the upthrust would increase the lower the boat sat, as more water was displaced; eventually the water overflows out of the boat and it sinks.

Answers to Worksheet 2.1.8 2. a) Balance 10 N; forcemeter 7 N. b) Balance 13 N ; forcemeter 4 N. c) Balance 11.5 N ; forcemeter 5.5 N. d) Balance 17 N ; forcemeter 0 N. 3. a) A with ii B with iv C with iii D with i. D must contain lead because lead is the densest of the materials involved and so will sink. C must be a tube of water in a beaker of salt solution because it is most buoyant; it is the least dense liquid in the tube and the most dense in the beaker. B is the opposite case to C. A is between B and C because the tube and beaker contain liquids of equal densities (water). b) The glass and bung of the boiling tube must be more dense than water.

Answers to Practical sheet 2.1.8 1. Always the same. 2. Much lower. 3. The difference between the forcemeter reading in air and that when submerged in water. Key Stage 3 Science Teacher Pack 2

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Chapter 1: Forces

2.1.9 Checking students' progress The ‘Checking your progress’ section in the Student Book indicates the key ideas developed in this chapter and shows how students progress to more complex levels. It is provided to support students in:

• identifying the key ideas • developing a sense of their current level of understanding • developing a sense of what the next steps in their learning are. It is designed either to be used at the end of a chapter to support an overall view of progress, or alternatively during the teaching of the chapter. Students can self-assess or peer assess using this as a basis. It would be helpful if students can be encouraged to provide evidence from their understanding or their notes to support their judgments. In some cases it may be useful to explore the difference in the descriptors for a particular idea so that students can see what makes for a ‘higher outcome’. It may be useful with some descriptors to provide examples from the specific work done, such as an experiment undertaken or an explanation developed and recorded. If marking and feedback use similar ideas and phrases, this will enable students to relate specific marking to a more general sense of progress.

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Chapter 1: Forces

To make good progress in understanding science students need to focus on these ideas and skills: Students who are making modest progress will be able to:

Students who are making good progress will be able to:

Students who are making excellent progress will be able to:

Represent forces using force diagrams.

Describe the size and direction of forces using force diagrams.

Explain how the size and direction of forces determines their effects.

Describe how materials behave when subjected to forces of tension or compression.

Explain the relationship between the amount of change in shape and the size of the force.

Explain that, in some materials, the change is proportional to the force applied.

Explain that friction is a contact force opposing the direction of movement.

Identify factors which affect the size of frictional and drag forces.

Evaluate how well a design reduces frictional or drag forces.

Recall that if the forces on an object cancel out that it is in equilibrium.

Explain that if a resultant force is zero, the object will remain at rest or continue to travel in a straight line at a steady speed.

Apply ideas about resultant forces and equilibrium to unfamiliar contexts.

Describe the causes and effects of varying pressure on and by solids.

Explain how force and area can be varied to alter the pressure applied.

Calculate the pressure applied by a solid from the force applied and the contact surface area.

Describe the variation of pressure in liquids with depth and the effects of this.

Explain the variation of pressure with depth in liquids.

Identify the causes and implications of variation of pressure with depth.

Explain why some objects float and others sink.

Use the concepts of density, displacement and upthrust in explaining floating and sinking.

Apply ideas about density and upthrust to predict the outcomes of various situations.

Describe how atmospheric pressure varies with height; state some implications of variations in pressure.

Explain why atmospheric pressure varies with height; describe how the effects of pressure are used and dealt with.

Identify some implications of pressure variation in situations such as weather patterns and high-altitude activities.

Recognise that pressure acts in a fluid in all directions.

Explain how liquids are used in hydraulic systems to transmit forces.

Carry out calculations relating to hydraulic systems in which the applied forces are increased.

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Chapter 1: Forces

2.1.10 Answers to Student Book questions This table provides answers to the ‘Questions’ section at the end of Chapter 1 of the Student Book. It also shows how different questions assess attainment in terms of the focus and style of a question as well as the context. Question level analysis can indicate students’ proficiency in approaching different aspects of scientific understanding and different types of answer.

2

d

1

x

x

x

3

d

1

x

x

x

4

a

1

x

x

x

5

c

1

x

x

x

6

10 N (resultant) pushing force

1

x

x

x

The scooter will get faster/accelerate

1

x

x

x

Density of wood < density of water

1

x

x

x

Density of steel > density of water

1

x

x

x

The downward force of each chair leg would be spread over a larger area …

1

x

x

x

… so the pressure on the floor would be reduced

1

x

x

x

9

A = B = D (all have load of same mass), C

2

x

x

x

10

d

1

x

x

x

11

Reference to low % of oxygen

1

x

x

x

Reference to drop in fitness

1

x

x

x

Reference to acclimatisation

1

x

x

x

Reference to fitness being never as good as at sea level

1

x

x

x

Total possible:

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8

5

4

7

6

4

4

Pressure

x

Contact forces

x

Longer written answer

x

8

Context

Short written answer

1

Objective test question

d

Evaluation of evidence

1

7

Style

Application

Focus

Knowledge & understanding

Answer

Marks available

Q

13

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