Handbook p8 forces and motion

Agastya International Foundation

Forces and Motion Handbook P8

“To every action there is always opposed an equal reaction.”

-Isaac Newton (1643-1727)

1

HANDBOOK P8 FORCES AND MOTION OVERVIEW OF HANDBOOK ABL

CONCEPT Force Types of Force Introduction to Motion Types of Motion Characteristics of Motion

NO OF ACTIVITIES 2 1 2 4 3

TIME (min) 40 60 35 55 70

ABL 1 ABL 2 ABL 3 ABL 4 ABL 5 ABL 6

Laws of Motion

4

60

ABLs WITH REFERENCE TO STANDARD S.No. 1 2 3 4 5

STANDARD 7 6, 9 9 9 9

RELEVANT ABL ABL1, ABL 2 ABL 3 ABL 4 ABL 5 ABL 6

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PAGE NO

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LIST OF FIGURES, CHARTS AND WORKSHEETS S. No Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Chart 1 Chart 2 Chart 3 Worksheet 1 Worksheet 2 Worksheet 3 Worksheet 4

Name Newton’s colour disk Curved (Cycloidal) path model Speed velocity model Inertia at rest model Inertia of motion model Balloon and straw activity Tin can model Objects at motion with respect to people standing near the tree Objects at motion with respect to passengers inside the car Examples of rotating objects with Axis Speed Velocity Acceleration Newton’s second law

Page No 29 35 38 46 46 53 53 20 20 28 39 39 41 50

Note to Instructor: All the figures in this handbook are for the Instructor’s reference only. The Charts need to be printed and shown to the learners during the course of the activity. Worksheets need to be printed out in advance for the learners. The number of worksheets required is mentioned in the Material List.

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ABL 1 - Force Activity

Learning objective

1.1

What is force?

1.2

How do we measure force?

Key messages 

Force is a push or pull upon an object that results in a change of the object's position, speed and direction of motion, or shape.  A force exerted on an object can be measured in Newtons. Earth exerts a force of attraction of approximately 1 N on a 100 g mass.

Total

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Time (min) 25

15

40

4

ABL 1.1

Time: 25 min

LEARNING OBJECTIVE – What is force?

Note to Instructor – These activities show that any push or pull that changes an object’s position, shape, or speed and direction is a force.

ADVANCE PREPARATION Material List Material 1 Long, thick rope (for tug of war) (5 meters) 2 Sponge

Number Required 1 per class 1 per group

Things to do Not Applicable

Safety Precautions Handle the rope carefully. Friction on the rope will cause a burning-like sensation on the hands of the students.

SESSION Link to known information/previous activity Not Applicable Procedure Divide the class into 3 groups. Each group will perform one part of the activity.

Assign each of your three groups to one activity described below.

SESSION 1.1a Tug-of-war The first group will play tug-of-war.

Start the tug-of-war activity by finding the middle of the rope and marking it with a knot or a marker. To play tug of war, straighten the rope and put the two teams on separate sides of the rope. Have someone stand next to the middle-marker of the rope. Have the students start "pulling" on the rope. The team that moves the marker a certain distance from the person in the middle wins. It is very easy to tell who wins.

For the first game of tug-of-war, divide the students into two very uneven teams. For example, if there are seven students, put them in one team of two students and another team of five students. The team with more students will win.

Then start a new game of tug-of-war. This time the teams need to be as even as possible. The game will last much longer.

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SESSION 1.1b Arm wrestling The second group will arm-wrestle.

Have a pair of students sit facing each other, with a desk or table between them. The students will rest their right elbows on the table and grab hands, as if to shake hands. Each student will attempt to push the other student’s hand down to the table. Whoever pushes the other student’s hand to the table first is the winner.

SESSION 1.1c Squeezing a Sponge The third group will be squeezing a sponge. Have the students pass around the sponge, with each one given a chance to squeeze it.

UNDERSTANDING THE ACTIVITY Leading questions 1.1a Tug-of-war 1. Which group won the first game?

2. What did the group do to win?

3. Why did the other group lose?

4. Why did the second game take longer to finish than the first?

5. What is the difference between the two groups?

1.1b Arm wrestling 1. Who won the game?

2. What did the winner do to win?

3. Why did the other student lose?

1.1c Squeezing a Sponge 1. What happened to the shape of the sponge as you squeezed it?

2. Why do you think that the shape of the sponge changed?

1.1 Summary 1. What was common in all three activities?

Discussion and Explanation  In tug of war, the teams pulled the rope in opposite directions. The team which pulled more strongly won, and this stronger pull is nothing but a stronger force applied. When a strong force was applied to the rope, it moved so the other team got pulled.  The force changed the position of the rope and the students holding the rope. Force causes a change in the position of objects.

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6   

In the arm wrestling game, the pair of students applied force on each other from opposite sides.

The student who applied a stronger push won the game, so the force exerted by each player is in the form of push; stronger push wins.

In squeezing the sponge, students applied force on the sponge with their fingers, which resulted in a change of the shape of the sponge.

Forces can change the position, speed and direction of motion of objects, and shape of objects.

KEY MESSAGES 

Force is a push or pull upon an object that results in a change of the object's position, speed and direction of motion, or shape.

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LEARNING CHECK In the following activities, determine whether the force applied is a pushing or a pulling force, and check the appropriate box.

1

Activity Sucking juice

2

Erasing/Rubbing black board

3

Magnet attracting nails

4

Fruits falling from trees

5

Lifting weight

Diagram

Push

(Answers: 1. Pull; 2.Push; 3.Pull; 4.Pull; 5.Both (Pull by arms and push by feet).

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Pull

Both

8 Time: 15 min

ABL 1.2 LEARNING OBJECTIVE – How do we measure force?

Note to Instructor – Students will discover that we can measure gravitational force with a spring balance.

ADVANCE PREPARATION Material List 1 2 3 4 5

Material Spring balance (1 kg) Rubber band Weights (50 to 200 g) Thread Vertical stand

Number Required 1 per group 1 per group 1 set per group 1 roll 1 per group

Things to do Adjust the pointers of the springs on the spring balances to coincide with zero.

Suspend the spring balances from the vertical stands with the thread.

Safety Precautions Do not put heavy weights on the spring balance.

SESSION Link to known information/previous activity We learned about a quantity called force. If force is a quantity, then it should be measurable. If we can’t see a force when it is applied, how can we measure it?

Procedure Fix the 100-gram weight to the hook of the spring balance and observe the readings of spring balance on both sides. Repeat the activity for different weights, including weights of 50 grams and 200 grams, and observe the readings of the spring balance.

UNDERSTANDING THE ACTIVITY Leading questions 1. What happens to the readings of the spring balance as you increase the weights? Why is that so?

2. What are the units marked on the spring balance?

3. How is force exerted on the spring balance?

Discussion and explanation  When a weight is suspended on the spring balance, it exerts a force (pull) on the spring balance, resulting in the downward movement of the pointer. (Actually the earth attracts the weight Agastya International Foundation. For Internal Circulation only.

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  

towards it; the weight, in turn, pulls the spring in the balance). The balance readings show how much force (pull) is exerted by the weight.

In the first case, the pointer shows nearly 1 newton with a 100-gram weight. This means that 100 grams of weight exerts a force of 1 newton on the spring balance.

Similarly, a 200-gram weight exerts approximately 2 newtons of force. We see that force is measured in newtons.

A newton (N) is the unit of force in the M.K.S. system.

KEY MESSAGES 

A force exerted on an object can be measured in Newtons. Earth exerts a force of attraction of approximately 1 N on a 100 g mass.

LEARNING CHECK How much force does a typical book exert on earth? A 7th-standard student?

(Answers: A typical paperback novel has a mass of about 0.5 kg, so it weighs approximately 5 N. This means that the earth attracts the book towards itself with a force of 5 N and the book exerts the same force on the earth. Similarly, a 7th-standard student has a mass of between 40 and 50 kg, so he/she weighs 400 to 500 N! It also means that the earth attracts the student towards itself with a force of 400 to 500 newtons and the student also exerts the same force on the earth.)

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10

ABL 2–Types of Force Activity

Learning objective

2.1

What are the types of forces?

Key messages 

A force that is exerted when one object comes into contact with another is called a contact force.

Muscular force, tension, and friction are the contact forces.  A non-contact force is a force applied to an object by another body that is not in direct contact with it. Magnetic force, electrostatic force, and gravitational force are the noncontact forces.

Total

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Time (min) 60

60

11

ABL 2.1

Time: 60 min

LEARNING OBJECTIVE – What are the types of forces?

Note to Instructor – These activities demonstrate the following forces: muscular force, friction, tension, magnetic force, electrostatic force, and gravitation.

ADVANCE PREPARATION Material List Material 1 Bar Magnet, pencil 2 Iron Nail 3 Marker/Chalk 4 Small wooden block (10 cm x 10 cm; smooth on one surface and rough on other surface) 5 Thread 6 Spring balance 7 Rubber band 8 Vertical stand 9 Slotted weights (50 g to 500 g) 10 Pencil 11 Nylon/cotton cloth 12 Straw 13 Plastic covers 14 Scissors 15 Plastic balls, papers, chalk pieces, etc.

Number Required 1 each per group 1 per group 1 per group 1 per group 1 roll per class 1 per group 1 per group 1 per group 1 set per group 1 per group 1 per group 1 pack per class 2 square meters 1 per group Several per group

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the previous activity, we learned how to measure force by measuring the force a weight exerts on a spring balance. This is not the only kind of force that we might want to measure; what other kinds of forces are there?

Procedure SESSION 2.1a Agastya International Foundation. For Internal Circulation only.

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12 Contact and non-contact forces Mark two points A and B on the table with some distance between them (at least 20 cm). Place a nail at point A, and ask one of the students to displace the nail to point B using a pencil.. He or she will move the nail by pushing the nail by the pencil.

Now challenge the other students to bring back the nail from point B to point A without touching the nail.

(Hint: use a magnet!)

SESSION 2.1b Muscular force Ask the students to jump, run, and exercise for few minutes.

SESSION 2.1c Friction Place a wooden block on the floor with the smooth surface touching the ground, and fix the spring balance to the wooden block with the thread. Gently drag the wooden block on the floor for a distance of 20 cm, and note down the readings of spring balance.

Repeat the activity with the wooden block inverted, so rough surface is touching the ground.

SESSION 2.1d Tension Suspend a spring balance from a vertical stand with thread, and then fix a rubber band to the hook of the spring balance. Hang a weight of 100 g to the rubber band. Observe what happens to the rubber band.

Add different weights to the rubber band, such as 200 g, 300 g, or 400 g, and observe what happens to the rubber band each time.

SESSION 2.1e Magnetic force Suspend an iron nail from the vertical stand. Make the nail stay still without swinging, and ask the students to bring a bar magnet slowly near the nail. Once the nail is attracted by the magnet, move the magnet around the nail and observe the motion of the nail.

SESSION 2.1f Electrostatic force Attach a sharpened pencil horizontally to the vertical stand. Take a straw and bring it near to the sharpened end without touching the pencil. Now rub one end of the straw with nylon/cotton cloth and again bring it near to the sharpened end of the pencil without touching the pencil. After the pencil is attracted to the straw, move the straw around the pencil. Observe the motion of the pencil.

SESSION 2.1g Gravitation Throw a few lightweight objects like plastic balls, papers, and chalk pieces upwards and observe their motion.

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UNDERSTANDING THE ACTIVITY 2.1a Contact and non-contact forces Leading questions 1. How did you displace the nail from point A to point B? 2. How did you displace the nail from point B to point A? 3. What is the difference between the two cases?

Discussion and Explanation  In the first case, the student pushed the nail by a pencil touching the nail and by exerting a force by his hand. and in the second case, the nail was pulled back without anything touching or holding it.

In both cases, the movement took place but the method of creating the movement was different.  As we know, a pull or push is a force, so in both cases force is exerted on the nail to displace it.  In the first case, we have exerted the force by contacting the nail. The force exerted when the objects are in contact with each other is called a contact force.  In the second case, we pulled the nail back to point A without touching it. Here the magnet exerted a force on the nail without touching the nail; such a force, where there is no contact between the objects, is called a non-contact force.

2.1b Muscular force Leading questions 1. Which body parts are in use during the exercise?

2. What is the type of force you use for jumping and running?

Discussion and Explanation  During activities like jumping and running, our muscles are at work. These actions are caused by the contraction and relaxation of our muscles. The force exerted during this contraction and relaxation of our muscles is called muscular force.  All our physical activities, like walking, laughing, yawning, jumping, writing, sitting, pulling, pushing, and typing, use muscular force.

Muscular force is a contact force.

2.1c Friction Leading questions 1. In which case was it easier to drag the wooden block?

2. Why did the wooden block set on its rough surface require more force to drag?

Discussion and Explanation  It was easier to drag the wooden block when it was placed on its smooth surface and we used more force to drag it when it was set on its rough surface.

When an object slides on another object, an unseen force develops that opposes the sliding. This force is called frictional force or friction.  When we dragged the wooden blocks, in both cases we used force to overcome the frictional force.

In the first case, when the wooden block was on its smooth surface, the friction was less so we Agastya International Foundation. For Internal Circulation only.

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14 needed less force for dragging. When the block was on its rough surface, due to uneven contacting surfaces, more friction developed, so we used more force to drag the same wooden block.

Friction develops as the opposing force when two objects in contact are trying to move with respect to each other, so friction is always a contact force. However, the force causing the motion of one object with respect to the other may be a contact force or a non-contact force.

2.1d Tension Leading questions 1. Why did the rubber band stretch as the weights were hung?

2. What happened to the rubber band when more weight was added?

3. Why did the rubber band return to its original state once the weights were removed?

Discussion and Explanation  When the weights are hung on the rubber band, it stretches as the weight increases. When more weights are added, it continues stretching and eventually breaks.  When a weight is attached to a rubber band, the weight exerts force on the rubber band by pulling downwards, and at the same time, the rubber band opposes this downward pull by the weight. This opposing force that develops in the rubber band is called tension. The tension is always equal to the downward pull due to the weight at equilibrium, that is the weight is not moving downwards or upwards.  When the suspended weight and therefore its pull are greater than a certain value, the tension in the rubber band exceeds its inherent strength; then the rubber band breaks.  Tension is a contact force and is commonly seen in ropes, strings, and wires.

2.1e Magnetic force Leading questions 1. Why did the magnet attract the iron nail?

2. Can you name what force this is?

3. Can you find such forces anywhere in your day-to-day life?

4. Is the magnetic force a contact or non-contact force?

Discussion and Explanation  When the magnet is brought near the iron nail, the nail comes closer to the magnet because magnets exert a force (pull) on nails, which are made of a magnetic material. This magnetic pull is called magnetic force. (Note: If the nails were made of brass or plastic, they will not be attracted by the magnet. Iron is a magnetic material though it is not a magnet by itself.)  The magnet and nail are not in contact with each other but still the magnet exerts force, so this force is a non-contact force.  When two magnets with same pole are brought closer to each other, they move apart.  When two magnets with opposing poles are brought near each other, they stick together.  Every magnet exerts a force (push or pull) on every other magnet. This force is also called magnetic force.  Magnetic force is the force exerted by a magnet on another magnet or on a magnetic material in attraction or repulsion.

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15 2.1f Electrostatic force Leading questions 1. What happened to the pencil when the un-rubbed straw was brought near it?

2. Why was the pencil attracted to the rubbed straw?

3. Which object is exerting a force, and on what?

4. Can you name the force demonstrated?

Discussion and Explanation  When an un-rubbed straw is brought near a sharpened pencil, no effect is observed; when a rubbed straw is brought, the pencil moves towards the straw. This is so because the rubbed straw exerts a force (pull) on the pencil.  The straw while being rubbed develops an electric charge on its rubbed surface.  When this charged straw is moved towards any uncharged object, the straw exerts a force on the uncharged object.  The force exerted by a charged object on another charged or uncharged object is called electrostatic force.

This is a non-contact force.

2.1g Gravitation Leading questions 1. Why do the objects that are thrown up, fall down?

2. If a ball is thrown up, why won’t it go up continuously?

3. What kind of force is this?

4. Do other planets exert such a force?

Discussion and Explanation  When the objects are thrown up, they travel up to a certain height and then fall down towards earth. This is due to the fact that the initial velocity given to the object by the force used in throwing the object upwards gets gradually overcome by the force of attraction exerted by the earth (called gravitational force).When the upward speed becomes zero, the gravitational force takes over fully and brings the object down towards the earth  This gravitational force is exerted between any two objects having mass. Gravitational force is an attractive force.  The weight of an object is the actual gravitational pull exerted on that object. Mass is different from weight.  Mass is the quantity of matter present in an object, and weight is the force of gravity acting upon an object. Mass is related to how much stuff there is, and weight is related to the pull of the Earth (or any other planet) upon that stuff.  The mass of an object (measured in kg) will be the same no matter where in the universe the object is located. Mass is never altered by location, the pull of gravity, speed or even the existence of other forces. For example, a 2-kg object will have a mass of 2 kg whether it is located on Earth, the moon, or Jupiter; its mass will be 2 kg whether it is moving or not (at least for the purposes of our study); and its mass will be 2 kg whether it is being pushed or not.  On the other hand, the weight of an object (measured in newtons) will vary according to where in the universe the object is. Weight depends on which planet is exerting the force and on the distance the object is from the planet.

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16

KEY MESSAGES  

A force that is exerted when one object comes into contact with another is called a contact force.

Muscular force, tension, and friction are the contact forces.

A non-contact force is a force applied to an object by another body that is not in direct contact with it. Magnetic force, electrostatic force, and gravitational force are the non-contact forces.

LEARNING CHECK Why do vehicle tires and shoes have strips on their outer surfaces? (Answer: To increase the friction between the vehicle or shoe and the ground) Why do we use lubricants and ball bearings in factories that produce machinery? (Answer: To reduce the friction on the piece of machinery and increase the speed at which it can be transported) If an obese person went to a doctor, and the doctor recommended that he start a diet, would the man be reducing his weight or his mass? (Answer: mass; to reduce his weight he should go to the moon! This is because “weight” depends on the gravitational pull on a body. The moon’s gravity is much less than that of the earth, therefore objects weigh much less there. If you jump on the moon, you will take a long time to return to the surface as compared to when you jump on earth!)

What are the units for weight? For mass? (Answer: newtons; kilograms). Please note that in daily life we commonly mention our weight in kilograms. Strictly speaking, this is not correct. When I say my weight is 50 kilograms, I should actually be understood as saying “my mass is 50 kilogram which will exert a force of nearly 50x10=500 newtons on earth.”

TRY IT YOURSELF Can you find examples of the following forces in action?  Pulling a kite string  Fruit falling from a tree  Pushing a shovel into the ground

INTERESTING INFORMATION Every object always has forces acting on it, including gravity and usually the normal force to oppose gravity. If the object is at rest, that means the forces just balance each other out!

Friction always opposes motion and makes you spend more energy.

But friction is not always a bad thing. Without some friction between your car and the road, you cannot move. The reason why cycle or motorcycle wheels slip on a wet road is the lack of sufficient friction!

Gravity does not make heavier objects fall down faster; a marble and a tennis ball would fall at the same speed towards the ground if not affected by any force other than gravity.

We say that objects are “weightless” in outer space, but really they just have very, very tiny weights, because they are very far from any other objects with mass. If gravity did not work in space, the Earth Agastya International Foundation. For Internal Circulation only.

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17 would not orbit the sun! Earth is just far enough away from the sun, and moving just quickly enough, to equal and cancel the pull exerted by the sun.

WEB RESOURCES www.le.ac.uk/se/centres/sci/selfstudy/fam5.html www.physics.montana.edu/physed/misconceptions/forces/forces.html www.science-class.net/Physics/force_motion.htm www.physicsclassroom.com/class/newtlaws/u212b.cfm

VOCABULARY 1) Force – A force is a push or pull on an object that results in a change of the object’s position, direction of motion, or shape.

2) Newton – A newton (N) is a unit for measuring force. A 100-gram weight exerts a force of nearly 1 N on Earth.

3) Contact force – A force exerted when the forcing object and the forced object are in contact 4) Non-contact force – A force exerted when the forcing object and forced object are not in contact 5) Muscular force – The force exerted by the contraction and relaxation of our muscles is the muscular force. It causes walking, laughing, yawning, jumping, writing, sitting, pulling, and typing, as well as any other physical activity.

6) Friction – A force that opposes the motion when one object slides on another object 7) Tension – A force exerted by ropes, strings, cables, and wires when they are pulled tight by objects at both end. If the tension increases too much, the rope or string will break.

8) Magnetic force – A force of attraction or repulsion exerted by a magnet on another magnet or magnetic material 9) Electrostatic force – A force exerted by a charged body on another charged or uncharged body 10) Gravitational force – A force exerted between any two objects having mass. Gravitational force usually refers to the effect of gravity exerted by Earth on an object that is on Earth.

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18

ABL 3 Introduction to Motion Activity

Learning objective

3.1

What are motion and rest?

3.2

Is motion relative?

Key messages

Time (min)  There are two states of an object: 15 at rest and in motion  An object is said to be at rest if there is no change in its position with respect to its surroundings in a given amount of time.  An object is said to be in motion if it changes its position with respect to its surroundings in a given amount of time.  Motion is relative, depending on 20 the relationship between the observer and the object being observed.

Total 35

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19 Time: 15 min

ABL 3.1 LEARNING OBJECTIVE – What are motion and rest?

Note to Instructor – This game shows the difference between being in motion and being at rest.

ADVANCE PREPARATION Material List Not Applicable.

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the previous ABL, we learned that a push or pull on an object is a force. Why are forces important – what do they do? They cause a state called motion. What is motion?

Procedure Play the statue (freezing) game: Ask all the students to perform some random movements like walking, running, jumping, rotating, or dancing. After a few seconds, the instructor will loudly say “statue”, and the students will freeze. If the number of students is large, play the game with 10 – 15 students and ask the other students to observe.

UNDERSTANDING THE ACTIVITY Leading questions 1. What were the students doing once the game started?

2. What happened as the instructors said “statue”?

3. What is the difference between these two situations? Can you name the two situations?

4. Give some examples of objects that are at rest, and objects that are in motion.

5. Can you imagine an object in a state other than rest or motion?

6. Can an object be at rest and in motion simultaneously?

Discussion and Explanation  When the game started, the students were moving, i.e. changing their positions from time to time.

We call that state, motion.  As the instructor said statue, all the students stopped their actions and movements and froze. Here their positions didn’t change and they could be said to be at rest.

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20  

Objects – living or non-living – can exist in one of only two states of motion.

Objects cannot have any states of motion other than motion and rest.

Some objects in motion are: o Planets moving around the sun o Objects thrown up from the earth o Animals travelling on the earth o Birds flying in the sky o Vehicles travelling on the road o Movement of the parts of machines o Heart beat

KEY MESSAGES   

There are two states of an object: at rest and in motion.

An object is said to be at rest if there is no change in its position with respect to its surroundings in a given amount of time.

An object is said to be in motion if it changes its position with respect to its surroundings in a given amount of time.

LEARNING CHECK Mark the object as at rest or in motion: Object condition The hands of a wall clock A cell phone kept on the table The wings of a bird while flying The branches of a tree on a windy day A car parked on the side of the road An apple falling from a tree A man sitting on a bus Blood circulation in a person sitting on a bench

At rest

In motion

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21

ABL 3.2 LEARNING OBJECTIVE – Is motion relative?

Note to Instructor – This skit shows that the motion of an object depends on the observer.This activity can be done in a field or in a classroom.

ADVANCE PREPARATION Material List 1 2

Material Charts Sketch pens

Number Required 3 per class 1 pack per class

Things to do Make three name boards named Tree, Car, and People. Student groups will wear these boards as they perform a skit.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the previous activity, we distinguished between the state of being at rest and the state of being in motion. Here we will learn that it is not quite so simple: if you are sitting in a car with your friend, he does not appear to you to be moving, even if your car is moving. How is that possible?

Procedure Play the following skit with three groups of students, each having 3 to 4 students. The groups will put on the name boards and perform.

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22

CHART 1 (Picture copied from IX standard AP Physics textbook, page 17)

CHART 2(Picture copied from IX standard AP Physics textbook, page 17) The first group of students will act like a tree at a roadside, the second group will act like people standing beside the tree and waiting for the bus, and the third group will act like a car and its passengers. The third group will walk past the tree and the people waiting, pretending to be a passing car. The car group should actually act like a person driving a car with two people behind acting like passengers.

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UNDERSTANDING THE ACTIVITY Leading questions 1. What is the state of the tree?

2. What is the state of the people waiting?

3. What is the state of the tree with respect to the people waiting?

4. What is the state of the people waiting with respect to the tree?

5. What is the state of the car?

6. What is state of the car with respect to the tree and the people waiting?

7. What is the state of the tree with respect to the car?

8. What is the state of the passengers sitting inside the car with respect to the driver?

9. What is the state of the driver with respect to the people waiting for the bus?

Discussion and explanation  The tree is at rest and the people waiting are also at rest.  The tree is at rest with respect to the people waiting  The people waiting are at rest with respect to the tree.  As the car passes, the car is in the state of motion with respect to the tree and people waiting, and the driver and passengers are in the state of motion with respect to the tree and people waiting.  For the passengers and driver, the tree and people waiting are in motion, but they are at rest with respect to each other.  Motion is a combined property of the observer and the object that is being observed.  Motion is a continuous change in the position of an object with time relative to the observer.

Hence, motion is relative.

KEY MESSAGES 

Motion is relative, depending on the relationship between the observer and the object being observed.

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LEARNING CHECK Mark the objects given in the table below as being at rest or in motion: Object A flying bird

A man on a bus

The hands of a clock

A boat on a river

Object Condition At rest The wings of a bird while flying, relative to someone standing on the ground The right wing of a bird with respect to its left wing The wings of the bird with respect to its beak A man sitting in a bus with respect to a man standing at the side of the road A man sitting in a bus with respect to another person on the bus The seconds hand of a wall clock with respect to the clock dial The hours hand of a wall clock with respect to the minutes hand A boat travelling down a river with respect to a person standing on the bank A steam-powered boat travelling down a river with respect to a person floating down the river on a log

In motion

Note to Instructor: When birds fly, their wings move together, so the left and right wing will be at rest relative to each other; both wings are in motion with respect to the bird’s beak

TRY IT YOURSELF The next time you ride in a car or on a two-wheeler, watch the motion of the vehicles around you. Pick two vehicles, and try to determine their state of motion relative to you, to each other, and to the side of the road.

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25 Watch the moon play “hide-and-seek” among clouds. The moon, which is quite far away, appears to move fast; but it is actually the clouds in the foreground which are moved by the wind. What we observe is the relative motion of the clouds with respect to the moon behind it.

INTERESTING INFORMATION Newton’s First Law of Motion states that an object at rest will remain at rest, and an object in uniform motion will remain in uniform motion, unless it is acted upon by an external force. (Uniform motion means movement along a straight line path at constant speed.)

The relationship between an observer and the object under observation is called the frame of reference, or sometimes the observational frame of reference.

Another example of relative motion is how the sun appears to move across the sky, when the earth is actually spinning and causing that apparent motion. Usually, we consider motion with respect to the ground or the Earth. Within the Universe there is no real fixed point. The basis for Einstein's Theory of Relativity is that all motion is relative to what you define as a fixed point.1

WEB RESOURCES http://hyperphysics.phy-astr.gsu.edu/hbase/relmot.html (another general explanation of relative motion) http://www.studyphysics.ca/newnotes/20/unit01_kinematicsdynamics/chp03_kinematics/lesson09.htm (several fabulous examples, fully explained)

VOCABULARY 1) Motion – A continuous change in the position of an object over time, relative to the observer 2) Rest – The state of motion of a body that has constant position with respect to the observer

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26

ABL 4- Types of Motion Activity

Learning objective

4.1

What is translatory motion?

4.2

What is oscillatory motion?

4.3

What is rotatory motion?

Key messages 

Time (min) 15

A body is said to be in translatory motion if it changes its position from one place to another place with all of its parts moving in the same direction.  The to-and-fro motion of an object 15 about a fixed point following a constant path between two end points is called oscillatory motion.  Motion where an object spins 15 around a fixed axis is called rotatory motion.

Total 45

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ABL 4.1

Time: 15 min

LEARNING OBJECTIVE – What is translatory motion?

For instructor only – This activity demonstrates translatory motion, that is, motion in a straight line.

ADVANCE PREPARATION Material List Material 1 Toy car 2 Thread 3 Permanent marker 4 Chalk 5 Meter stick

Number Required 1 per group 1 roll per class 1 per group 1 per group 1 per group

Things to do Attach a piece of thread to each toy car.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity We have learned how to relate an object in motion to its observer. Now we will learn how to distinguish between the different ways an object might be moving.

Procedure Take a toy car and mark two points, A and B, on the car. Place the car on the floor/table and mark two points, A and B, on the floor/table corresponding to the points on the car.

Pull the car a distance of 20 cm and mark two points A’ and B’ on the floor corresponding to the two points A and B on the car.

Measure the distance between the points A and A’ on the floor, and between the points B and B’ on the floor.

Ask students to observe the direction of motion of points A and B on the car.

UNDERSTANDING THE ACTIVITY Leading questions 1. What happened to the position of the car when it was pulled?

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28 2. Is the direction of motion of points A and B on the car the same as the direction of motion of the car?

3. Is the distance the same between the points A and A’ and between the points B and B’ on the floor?

Discussion and Explanation  When the car is pulled forward using a thread, the total body moves from one point to another point – that is, it changes position.  The points marked A and B also move in the direction of motion of the car. Every particle of the car moves along the direction of motion of the entire car.  The distance between the points A and A’ is the same as the distance between the points B and B’ on the floor.

The type of motion described above is called translational motion. If all of the parts of a moving body move in the direction of motion of the body, then it is said to be moving with translational motion.

If an object moves in the straight line, this is called rectilinear translatory motion.

If an object moves in a curved path, this is called curvilinear translatory motion. The motion of an arrow released from a bow is curvilinear translatory motion.

KEY MESSAGES 

A body is said to be in translatory motion if it changes its position from one place to another place with all of its parts moving in the same direction.

LEARNING CHECK Give some examples of objects in translatory motion. Include both curvilinear and rectilinear motion. [See learning check at the end of ABL 3.3)

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ABL 4.2

Time: 15 min

LEARNING OBJECTIVE – What is oscillatory motion?

For instructor only – These activities show that repetitive, back-and-forth motion is called oscillatory motion.

ADVANCE PREPARATION Material List Material 1 2

Vertical stand Thread

3

Glue/M. Seal

4 5 6

Rubber band Marbles Scissors

Number Required 1 per class 1 roll per class 1 bottle per class 1 per group 1 per class 1 per class

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the last activity we investigated translatory motion. Now we will learn what happens when translatory motion occurs in one direction and then back in the opposite direction to the starting point.

Procedure (Note to Instructor-Complete 4.2a as a demonstration, then complete 4.2b as a group activity. After completing both parts, ask all of the Leading Questions.)

SESSION 4.2a Marble Suspend the marble from the vertical stand with the help of thread and glue, and make the marble stop moving. Gently pull and release the marble, and observe its motion.

SESSION 4.2b Rubber band Take the rubber band and stretch it. Ask the students to pluck the rubber band and observe what happens to it.

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UNDERSTANDING THE ACTIVITY 4.2a Marble Leading questions 1. What happens to the marble as it is pulled?

2. What is the direction of motion of the marble?

3. Is the marble frequently coming to its starting position and going back?

Discussion and explanation  When the marble is suspended from a vertical stand (a fixed point) and it is pulled and released, it is set in motion. The motion of the marble is repetitive, which means that it travels to some distance and comes back to the starting position, and that this motion continues for a certain period of time.  To-and-fro motion of an object following a constant path around a fixed point is called oscillatory motion.  Oscillatory motion is interesting because it often takes a fixed amount of time for the object to go back and forth once. This kind of motion is said to be periodic; the time for one complete back-andforth cycle (called an oscillation) is called the period of oscillation.  Periodic motion is important in the study of sound, light, and other waves.  Large chunks of physics research are devoted to this kind of repetitive motion. (Doing the same thing over and over and going nowhere is pretty important!)

4.2b Rubber band Leading questions 1. What happens to the rubber band when it is plucked?

2. Can you see the motion of the rubber band?

3. Is the rubber band also frequently coming to its starting position and going back?

4. Are the motions of the marble and of the rubber band the same?

Discussion and explanation  When the rubber band is stretched and plucked, it moves up and down rapidly, i.e. it vibrates.

Therefore, it frequently returns to its original position. Here we can observe that this motion is different from that of the marble. The marble requires an external force to return to its original position, without which it will roll along the direction in which force was initially applied.  Motion where the object vibrates frequently is called vibratory motion. This is a type of oscillatory motion.

KEY MESSAGES 

The to-and-fro motion of an object about a fixed point following a constant path between two end points is called oscillatory motion.

LEARNING CHECK Give some examples of objects in oscillatory motion. [See learning check at the end of ABL 4.3)

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ABL 4.3

Time: 25 min

LEARNING OBJECTIVE – What is rotatory motion?

For instructor only – These activities show rotatory motion, in which an object spins in one place.

ADVANCE PREPARATION Material List Material 1 Cardboard sheet (5 cm2) 2 Pencil 3 Scissors 4 Pencil sharpener 5 Newton’s colour disk 6 Observation sheet for learning check on different kinds of motion (see page 31 below for sample sheet)

Number Required 1 per group 1 per group 1 per group 1 per group 1 per class 1 per group

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity We have seen two types of motion so far – translatory and oscillatory. Now we will discover one more type – rotatory.

Procedure Complete the following 3 activities. The first is a student-aided demo; the second is a group activity, and the third is an instructor demo.

SESSION 4.3a “Fugadi” game Call two students (preferably of the same sex) and ask them to clasp each other’s hands - (both right hands and both left hands are held so that the students’ arms are crossed. They then swing each other around increasing their speed gradually. Observe the motion of the students.

SESSION 4.3b Cardboard top Cut a circle out of the cardboard sheet and draw a point in the center. Make a hole at this point and put a pencil through the hole. Rotate the pencil with the cardboard like a spinning top. Observe the motion of the cardboard.

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32 Newton’s colour disk Observe the colours in the Newton’s colour disk. Rotate the disk and now observe the colour and the motion of the disk.

FIGURE 1 – NEWTON’S COLOUR DISK

UNDERSTANDING THE ACTIVITY Leading questions 1. Describe the motion of the students rotating.

2. Are the students rotating at a fixed point on the ground or moving away from the point?

3. Is the motion of the cardboard similar to the motion of the students in 3.3a?

4. Is the motion of the Newton’s disk similar to that of the spinning cardboard and the students rotating?

Discussion and Explanation  When the students rotate by holding their hands, they are said to be in rotatory motion. The students are spinning at a fixed position on the floor, or around a fixed vertical axis.  Similarly, the spinning cardboard disk and Newton’s colour disk also spin around a fixed axis, called the axis of rotation.  In the case of the cardboard disk activity, the pencil represents the axis of rotation.  The axis of rotation is an imaginary straight line perpendicular to the plane containing the motion.  This picture shows the axes of rotation for some common rotating objects:

2

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33 

CHART 3 – EXAMPLES OF ROTATING OBJECTS WITH AXIS Rotating around a fixed axis is called rotatory motion.

KEY MESSAGES 

Motion where an object spins around a fixed axis is called rotatory motion.

LEARNING CHECK Give some examples of objects in rotatory motion.  The earth rotates about an axis passing connecting the north and south poles. It completes one rotation in 24 hours – what we call “one day”.

Learning check for different types of motion Distribute the observation sheet given below. Ask the students to identify the types of motion and tick the appropriate box(es).

Observation sheet for learning check on types of motion Motion

Translatory

Oscillatory

Rotatory

1

2

3

4

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34 5

6

7

8

( Answers – 1.t; 2. T; 3.t and o; 4.o and r; 5. o and r; 6. r; 7. r; 8. r)

TRY IT YOURSELF Place a pencil on a smooth, flat surface (like a table). Find the centre point of the length of the pencil. Flick the pencil at this point. How does the pencil move? Again flick the pencil, but this time on one side of the centre point. Now how does it move? You have just demonstrated translatory and rotatory motion!3

INTERESTING INFORMATION A Wilberforce pendulum exhibits all three kinds of motion. It consists of a mass suspended from a helical spring, so the mass can rotate and twist the spring or bounce up and down and stretch the spring. If it is Agastya International Foundation. For Internal Circulation only.

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35 set correctly, the mass will alternate between purely translatory (up-and-down) oscillations and purely rotatory oscillations.4

WEB RESOURCES www.physics.in/motion (more detailed explanation) http://physics.info/motion/ http://www.physicsclassroom.com/class/waves/u10l0a.cfm (much more detail about oscillatory motion, including an explanation for why it occurs)

VOCABULARY 1) Translatory motion – Motion in which all parts of a moving body move uniformly in the same direction 2) Oscillatory motion – To-and-fro motion of an object following a constant path about a fixed point 3) Oscillation – An oscillation is one cycle of oscillatory motion.

4) Period – The period of an oscillatory motion is the length of time it takes to complete one oscillation.

5) Vibration – Rapid oscillatory motion of a rigid or elastic body 6) Rotatory motion – Motion in which an object spins about a fixed axis without a change in linear position 7) Axis of rotation – The straight line through the middle of a rotating body around which the body rotates

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ABL 5 - Characteristics of Motion Activity

Learning objective

5.1

Any motion is characterized by distance travelled and displacement from rest.

5.2

What are speed and velocity?

5.3

What is acceleration?

(What happens to velocity when it changes?)

Key messages 

Time (min) 15

Distance and displacement are characteristics of motion.  Distance is the total path length traversed by an object irrespective of the direction of travel.  Displacement is the shortest length between the starting and ending points of a path, denoting the direction also.  Velocity is distance covered in a 40 specified direction per unit time.  Speed is distance covered per unit time.  Acceleration is the rate of change 15 of velocity with respect to time.

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ABL 5.1

Time: 15 min

LEARNING OBJECTIVE – Any motion is characterized by distance travelled and displacement from rest.

Note to Instructor – This activity shows that distance is the length of a path travelled by an object, and displacement is the distance between the starting and ending points of that path, in a specified direction.

Distance is a scalar and displacement is a vector.

ADVANCE PREPARATION Material List Material 1 2

Curved path model Marbles

3 4

Inclined plane Thread

5 6 7

Meter stick Chalk or marker Measuring tape

Number Required 1 per class At least 1 per class 1 per class 1 roll per class 1 per class 1 per class 1 per class

Things to do Collect required materials.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity We have learned all about how motion works, and the different types of motion. But motion is a physical quantity; that means we can measure it! Here we will learn how to measure a motion.

Procedure Complete 5.1a, then ask the leading questions and discuss students’ responses. Then complete 5.1b.

SESSION 5.1a Marbles rolling Take the curved path model and release a marble across the curved path. Have students observe the path traversed by the marble and the direction of motion of the marble. Now release the marble along the inclined plane (straight path). Have students observe the path traversed by the marble and the direction of Agastya International Foundation. For Internal Circulation only.

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38 motion of the marble. Measure the distance along the inclined path and curved path with the help of thread and a meter stick.

FIGURE 2 – CURVED (CYCLOIDAL) PATH MODEL SESSION 5.1b Students walking Take the students to the field, and mark two points some distance apart (at least 2 meters). Ask one student to start walking from point A to point B in a straight line. Ask another student to walk from point A to point B in curved path; the student may take any path to reach point B. Measure the distance between the two points along the different paths walked by the students, and then find the shortest path.

UNDERSTANDING THE ACTIVITY Leading questions 1. When the marble is released on the curved path, what happens to the direction of motion of the marble? Is the direction changing or not changing?

2. When the marble is placed in the straight path, what happens to the direction of motion of the marble?

3. Do the curved path and straight path have the same length?

4. Which path allows the marble to travel the least distance?

5. What are the distance and displacement in this situation?

Discussion and Explanation  When the marble is released from the curved path, it changes its direction of motion continuously.

When the marble is released along the straight path, the direction of motion stays constant – while moving it has only one direction.  The marble placed on the straight path travelled in a particular direction and for a certain quantity of length (magnitude). This travelled path is known as displacement and is associated with a specific direction. It is therefore a vector quantity.  Displacement is the shortest distance between any two points, even if the path travelled was curved.  Vector quantities, like displacement, have both magnitude and direction.

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39     

The marble placed on the curved path travelled a certain length by changing its direction. It does not have a single direction of motion, but it did travel a quantity of length (magnitude); the length of this travelled path is called distance and it is a scalar quantity.

Scalar quantities, including distance, have magnitude only.

The length of a path traversed by a marble in a given interval of time is called distance.

The displacement is the shortest distance between the starting point and ending point of the path, in a specified direction.

Distance is a scalar, and has no specified direction; displacement is a vector, and has a particular direction.

KEY MESSAGES   

Distance and displacement are characteristics of motion.

Distance is the total path length traversed by an object irrespective of the direction of travel.

Displacement is the shortest length between the starting and ending points of a path, denoting the direction also.

LEARNING CHECK Draw the below diagram on a black board/white board and give the following problem to the learners.

An object starts from Point A, travels on a circular path, and returns to the starting point A. Measure the distance and displacement of the object for the following different paths: 1. A to B 2. A to C 3. A to D 4. A to E 5. A to A 6. C to E

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40 Hint 1:For distance, run the thread from A to B along the circle line, mark the end, and measure the length using a meter stick. For displacement, draw a straight line from A to B and measure its length using the meter stick. Repeat the same procedure for the other points.

Hint 2: The displacement from A to A is zero.

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41

ABL 5.2

Time: 40 min

LEARNING OBJECTIVE – What are speed and velocity?

Note to Instructor – This activity shows that speed is distance per unit time and velocity is displacement per unit time. Speed is a scalar and velocity is a vector.

ADVANCE PREPARATION Material List Material 1 Speed – Velocity model 2 Digital stop watch 3 Measuring tape 4 Marble 5 Thread 6 Scale

Number Required 1 per group 1 per group 1 per group 1 per group 1 per group 1 per group

Things to do Arrange the velocity – speed model on the floor. Place a book/object below one end of the board and give a small inclination.

Figure 3 – Speed Velocity model

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the last activity, we learned how to measure the motion of an object. Now we will learn to describe how quickly the motion happened.

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Procedure SESSION 5.2a Group activity - Speed Place the marble at the top end of the curved groove and release it. Measure the time of its journey from the top of the board to the base. Repeat the trail three times and find the average time (t). Measure the distance (s) of the curved path from top to the bottom with the help of thread and scale. Calculate s/t Distance s (m)

Time t (s)

Average time (t)

Time t2 (s)

Speed v= s/t (m/s)

t1 = t2 = t3= WORKSHEET 1 – Speed SESSION 5.2b Group activity - Velocity Place the marble at the top end of the straight groove and release it. Measure the time of its journey from the top of the board to the base. Repeat the trail three times and find the average time (t). Measure the distance (s) of the path from top to the bottom with the help of thread and scale. Calculate s/t Distance s (m)

Time t (s)

Average time (t)

Time t2 (s)

Velocity v= s/t (m/s)

t1 = t2 = t3 = WORKSHEET 2 - Velocity

UNDERSTANDING THE ACTIVITY Leading questions 1. Why do we term s/t as speed in 5.2a 2. Why do we term s/t as velocity in 5.2b Discussion and explanation  In 5.2a the marble is moving along a curved path. Its direction is changing continously. The distance covered per unit time is therefore speed. Or the rate of change of distance is speed.

Speed = s/t, is a scalar  In 5.2b the marble is moving along straight path down the plane, the direction of motion is always the same. The distance covered per unit time is its velocity. Or the rate of change of displacement is velocity.

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KEY MESSAGES  

Velocity is distance covered in a specified direction per unit time.

Speed is distance covered per unit time.

LEARNING CHECK 

Mark the situation as describing speed or velocity:

Situation 1. You are travelling on the highway, and you look at the speedometer. It says 60 km/hr.

2. You take a trip to visit your cousins. Your mother says that you will drive 80 km/hr north for 2 hours.

3. A flock of birds is migrating south for the winter. They will travel 20 km/hr south for 1 month.

4. A man ran around a park at 10 km/hr.

(Answers: speed; velocity; velocity; speed)

Speed Velocity



While on vacation, Aishwarya travelled 720 kilometers. The trip took 9 hours. What was her average speed? If she was travelling east, what was her average velocity?

(Answer: 80 km/hr; 80 km/hr east) 

A physics teacher walked 4 meters east, 2 meters south, 4 meters west, and finally 2 meters north.

The entire motion lasted for 24 seconds. Determine the average speed and the average velocity. 5 (Answer: speed is 12 meters in 24 seconds, or 0.5 m/s; velocity is 0 m/s)  A train covers 60 kilometers between 2 p.m. and 4 p.m. How fast was it going at 3 p.m.? 6 (Answer: You don’t know! The average speed was 30 km/hr, but that does not tell us anything about the instantaneous speed at 3 p.m.)

ABL 5.3

Time: 15 min

LEARNING OBJECTIVE – What is acceleration? (What happens to velocity when it changes?)

Note to Instructor – This activity shows that acceleration is a change in velocity over time.

ADVANCE PREPARATION Material List Material 1 Marble 2 Digital clock or stopwatch 3 Speed-Velocity model

Number Required At least 1 per class 1 per class 1 per class

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44 4 5 6

Measuring tape Observation sheets (sample in text below) Steel plate

1 per class 1 per group 1 per class

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity We saw in the last demo that the kinetic energy of the spring was used in the form of a force to push the funnel and ball. A force was applied to cause motion. Here, we will see how force and motion are related.

Procedure This activity is an instructor demo where students will record their observations of the demo. Divide students into groups, and distribute one observation sheet to each group. Ask groups to record readings as the experiment is performed. Ask students to help you complete the demonstration by taking time measurements.

Lay the model on the floor of your classroom. Place a textbook under one end, so that it lies at an angle.

Place the steel plate at the base of the board.

Assign one student to be in charge of keeping the time with the stopwatch.

Release the marble at the top of the board, and measure the time from the top of the board till the marble reaches the base.

Repeat the trail three times and record the average time (t) Measure the distance along the board from top to the base (s) The acceleration of the marble while it is moving down the board is given by a = 2s/t 2 This experiment may be repeated for different inclinations.

Trial

Distance s (m)

Time t1 (s)

Average time Acceleration a (2s/t2)

1 2 3 WORKSHEET 3 - Acceleration

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45 Leading Questions 1. What is responsible for starting the motion of the marble from the top?

2. How do you calculate the acceleration?

Discussion and Explanation  When the marble is released from the top it is under the continuous the action of a gravitational force, which is a part of its weight.  It runs down with a uniform acceleration. Hence the time of journey from top to the base would be the same for all the trials. s/t gives average velocity and 2s/t gives the final velocity at the base. From the relation v =u+ at, { a = (v – u)/t} the acceleration is the rate of change of velocity.

2s/t = 0 + at, a = 2s/t2 Thus the acceleration of the marble rolling down the plane is measurable

KEY MESSAGES 

Acceleration is the rate of change of velocity with respect to time.

LEARNING CHECK Please say whether the following statements are true or false.

Statement True False 1 Speed is distance in miles per unit time in seconds 2 The rate of change of velocity is called acceleration 3 Speed is velocity with a given direction 4 If you throw a ball up in the air, it will first decelerate and then accelerate 5 Acceleration is always in the direction of motion 6 An object can have nonzero acceleration even if its speed is constant (Answers: 1. F – speed can be given with any units of distance and time, and is usually defined in terms of meters/second; 2. T; 3. F – velocity is speed with a given direction; 4. F – the acceleration of a ball thrown up is constant and does not change sign; 5. F – if an object is slowing down (decelerating), its acceleration is in the opposite direction from its motion; 6. T – acceleration is the change in velocity with time, not the change in speed, and velocity can be changing (circular motion) when speed is not)

TRY IT YOURSELF The next time you travel by vehicle, observe the speedometer at some point on your trip. After you arrive, record the time spent and the distance travelled, and calculate your average speed. How does the speedometer speed relate to your average speed? Can you guess the acceleration of the car/motorcycle at that point?

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INTERESTING INFORMATION Car speedometers7 The speedometer of a car reveals information about the instantaneous speed of your car. It shows your speed at a particular instant in time. If you were to inspect the speedometer readings at regular intervals, you would notice that it changes often.

The instantaneous speed of an object is not to be confused with the average speed. Average speed is a measure of the distance traveled in a given period of time; it is sometimes referred to as the distance per time ratio.

Common speeds of moving objects8 For human beings, an average walking speed is about 5 km/h, or 1.39m/s.

The speed of long distance jogging for an average person is about 10 km/h or 2.7 m/s.

Top athletic sprinters can run at 36.85 km/h or 10.24 m/s within a short distance such as a 200 meter dash.

Cycling can average 20 km/h or 5.56 m/s.

Cars can average 104 km/h or 28.9 m/s on the highway.

A 747 Airplane has an average speed of 909 km/hr.

WEB RESOURCES http://physics.info/displacement/ http://www.physicsclassroom.com/class/1dkin/U1L1b.cfm (scalars and vectors) www.physics.info/speed

http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm (speed and velocity) http://www.physicsclassroom.com/mmedia/kinema/trip.cfm (average and instantaneous speed) https://is.muni.cz/do/fsps/e-learning/33246712/Biomechanics/19.html (projectile motion under constant acceleration)

VOCABULARY 1) 2) 3) 4)

Vector – A quantity specified by a magnitude and a direction Scalar – A quantity specified by a magnitude with no direction Distance – The length of a path travelled by an object Displacement – The vector measure of the distance between the starting and ending points of the path travelled by an object, expressed with a direction 5) Speed – The rate of change of distance with respect to time 6) Velocity – The rate of change of displacement with respect to time 7) Acceleration – The rate of change of velocity with respect to time

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ABL 6- Laws of Motion Activity

Learning objective

Key messages

6.1

What is Newton’s First Law?



6.2

What is Newton’s Second Law?How to measure the force related to a body in motion?



An object at rest remains at rest, and an object in motion remains in motion, unless acted on by an external force.

Newton’s second law states that 15 the quantity of a force being applied is equal to the product of the mass it acts on and the acceleration it causes.

6.3

What is Newton’s Third Law?



15

Newton’s third law states that every action exists with an equal and opposite reaction.

Total

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Time (min) 30

60

48

ABL 6.1

Time: 30 min

LEARNING OBJECTIVE – What is Newton’s first law?

Note to Instructor – Students will understand the inertia of rest and inertia of motion properties and be able to describe situations where they can be applied.

ADVANCE PREPARATION Material List Material 1 Inertia at Rest model (plate and coin) 2 Carrom board coins 3 Striker 4 Inertia of Motion model (with ball and funnel)

Number Required 1 per class At least 5 per group 1 per group 1 per class

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity In the previous ABL, we learned how to measure motion and describe it quantitatively. Now we will investigate a qualitative property of motion.

Procedure 6.1a is an instructor demo, using the Inertia at Rest model. 6.1b is a group activity, using carrom board coins and a striker. 6.1a and 6.1b show exactly the same thing; the second activity just allows students to try it for themselves. 6.1c is a second instructor demo, using the Inertia of Motion model. Complete 6.1a and 6.1b, then discuss the first set of leading questions, and then complete 6.1c and discuss the second set of leading questions.

SESSION 6.1a Instructor demo Take the Inertia at Rest model. Place the coin on the plate. Strike the plate quickly. Ask students to observe what happens to the coin – does it fall in the stand or does it slip forward?

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FIGURE 4 – INERTIA AT REST MODEL SESSION 6.1b Group activity Distribute the carrom board coins to the students and ask them to arrange the coins in a pile. Make it clear that they will be observing the exact same thing as you demonstrated in 6.1a, and this version is just easier to do as a group activity.

A student should hit the bottommost coin using the striker. Ask students to observe the other coins – what happens?

SESSION 6.1c Instructor demo Take the Inertia of Motion model and put the ball on the funnel. Press the funnel and release. Have students observe the motion of the ball and funnel.

FIGURE 5 – INERTIA OF MOTION MODEL

UNDERSTANDING THE ACTIVITY Discussion Item 1 – Inertia of rest Agastya International Foundation. For Internal Circulation only.

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Leading questions 1. What happens to the coin in the instructor demo?

2. What happens to the stack of coins in the group activity?

Discussion and Explanation  When the plate is struck quickly, the coin falls into the cylinder, because we are applying force only to the plate and not to the coin. If we want to push the coin we have to apply force to the coin.  We can say that the coin is at rest and will continue to be at rest unless an external force compels it to change its position. This property is called inertia.  In simple words, inertia is the tendency of a body to remain in a state of rest or in continuous motion.  When the bottommost coin of the stack of coins is hit by the striker, then the other coins will stay in a stack and only the bottommost coin will move forward. Here we apply force only to the bottommost coin so it moves forward while the others remain stationary.  From the above two activities, we can say that objects at rest remain at rest if no external force acts on them. This property of rest is called inertia of rest.

Discussion Item 2 – Inertia of motion Leading questions 1. When we press the ball and funnel, they move down. When they are released, they move up. But the ball moves more than the funnel. Why? Discussion and explanation  When we press the ball and funnel, both move down. When they are released, they move up. But the ball moves more than the funnel. Why?  Here, the funnel is connected to a spring, so when we press the funnel, the spring gains potential energy. When the funnel is released, this is converted to kinetic energy. This energy is used in the form of a force to push both the funnel and the ball. But the funnel is stopped by the spring, while no external force is applied to the ball, so the ball continues in its motion.  This is called inertia of motion - the property that an object in motion will remain in motion continuously unless an external force acts on it.

KEY MESSAGES 

An object at rest remains at rest, and an object in motion remains in motion, unless acted on by an external force.

LEARNING CHECK Activity for students  Ask some students to stand up and turn round and round while standing in the same place, and then ask them to stop suddenly. Ask other students to run forward, and then ask them to stop suddenly.

Give a real-life application of the inertia of rest principle.

(Possible answers:  When a bus at rest moves forward, then the passengers fall backward due to their inertia.

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51 

When you hit a blanket with a stick, then the dust is removed due to its inertia.)

Give a real-life application of the inertia of motion principle.

(Possible answers:  When a fast-moving bus stops suddenly, the standing passengers fall forward because of their inertia of motion. The external force that stops the bus is provided by the brake. However, the passengers who were in forward motion with the bus will fall forward unless they are holding on to something.  You have probably seen a long jump athlete. She runs for a long distance before the jump to increase her inertia of motion.)

Consider the situations below to determine whether or not there is an external force acting on the airplane. Remember that according to Newton's First Law, a plane will resist a change in its state of rest or motion unlessit is acted on by a force.9 a. The airplane is flying at 200 kph at an elevation of 10,000 m. b. The airplane turns northeast at 200 kph and an elevation of 10,000 m. c. The airplane increases its speed to 220 kph at the same elevation. d. The airplane continues flying at 220 kph at 10,000 m. e. The airplane drops to an elevation of 9,000 m. f. The airplane heads due east maintaining its speed and elevation.

(Answers: a. no force; b. force; c. force; d. no force; e. force; f. no force)

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ABL 6.2

Time: 15 min

LEARNING OBJECTIVE – What is Newton’s Second Law? How to measure the force related to a body in motion?

Note to Instructor – Students will learn how force and motion are related and will learn how to use the equation F = ma, where F is force, m is mass, and a is acceleration.

ADVANCE PREPARATION Material List Material 1 Marble 2 Digital clock or stopwatch 3 Speed-Velocity model 4 Measuring tape 5 Observation sheets (sample in text below) 6 Spring balance (0 - 200 gm) 7 Steel plate

Number Required At least 1 per class 1 per class 1 per class 1 per class 1 per group 1 per class 1 per class

Things to do Not Applicable.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity We saw in the last demo that the kinetic energy of the spring was used in the form of a force to push the funnel and ball. A force was applied to cause motion. Here, we will see how force and motion are related.

Procedure This activity is an instructor demo where students will record their observations of the demo. Divide students into groups, and distribute one observation sheet to each group. Ask groups to record readings as the experiment is performed. Ask students to help you complete the demonstration by taking time measurements.

Lay the model on the floor of your classroom. Place a textbook under one end, so that it lies at an angle.

Place the steel plate at the base of the board.

Assign one student to be in charge of keeping the time with the stopwatch.

Release the marble at the top of the board, and measure the time from the top of the board till the marble reaches the base.

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Repeat the trail three times and record the average time (t) Measure the distance along the board from top to the base (s) The acceleration of the marble while it is moving down the board is given by a = 2s/t 2 Find the mass of the marble using a spring balance. Record this massm (in kg) in your observation tables.

Now calculate the product of m and a. Record these values in your tables.

This experiment may be repeated for different inclinations.

Trial

Distance s (m)

Time t1 (s)

Average time Acceleration a (2s/t2)

Mass m (kg)

F = ma

1 2 3 WORKSHEET 4 – Newton’s second law

UNDERSTANDING THE ACTIVITY Leading questions 1. Is the time measured the same for all the three trials?

2. Why does the marble start moving down when released from the top?

3. What does the last column in the table represent?

4. What change do you observe if the experiment is repeated for a larger inclination?

Discussion and Explanation  The time measured is more or less the same for all three trials. This is why we are able to use an average time in our calculations.  When the marble is released from the top it is under the continuous the action of a gravitational force, which is a part of its weight.  It runs down with a uniform acceleration. Hence the time of journey from top to the base would be the same for all the trials.  s/t gives average velocity and 2s/t gives the final velocity at the base. From the relation v =u+ at, 2s/t = 0 + at, a = 2s/t2  Thus the acceleration of the marble rolling down the plane is measurable  From Newton’s second law, the force driving the marble down the plane is , F = ma m is known, a is measured and thus F is measured.

The last column in the table represents the force acting on the marble.  On increasing the inclination, the gravitational force acting on the marble increases. The acceleration measured also increases.

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KEY MESSAGES 

Newton’s second law states that the quantity of a force being applied to an object is equal to the product of the mass it acts on and the acceleration it causes.

LEARNING CHECK If the mass of a body is tripled, what must happen to the force for its acceleration to remain constant?

(Answer: The force must be tripled as well. This is why some trains run with 2 engines when they pull extra coaches!)

Suppose that a sled is accelerating at a rate of 2 m/s 2. a. If the net force is tripled and the mass is doubled, then what is the new acceleration of the sled? b. If the net force is tripled and the mass is halved, then what is the new acceleration of the sled? 10 (Answer: a. 3 m/s2; b. 12 m/s2) How much force is required for a body to maintain uniform motion in a straight line?

(Answer: None! The acceleration is zero.)

We know that acceleration is a vector quantity from ABL 4.3. Mass is a scalar quantity. Is force a vector or a scalar?

(Answer: A vector)

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Time: 15 min

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ABL 6.3 LEARNING OBJECTIVE – What is Newton’s Third Law? Note to Instructor – These activities demonstrate that a reaction force accompanies every action force.

ADVANCE PREPARATION Material List Material 1 Balloon 2 Thread 3 String of 5 meters length 4 Scissors 5 Straw 6 Set of 3 Tins of the same size with holes at bottom; all the tins have two holes diametrically opposite near the top. Strings are passed through these holes as shown in FIGURE 7, so that the tin can be held up over a basin of water.

7 8

Tin 1 will have two holes pierced diametrically opposite each other near the base. Tin 2 will have two tangential holes pierced diametrically opposite each other near the base. The holes are pierced in such a way that water will flow out in opposite directions. Tin 3 will have two pairs of tangential holes pierced diametrically opposite each other near the base, so there are four holes at 90 degree intervals Cello tape Water in a plastic basin and a small plastic cup for pouring water into the tins

Number Required 1 per group 1 roll per class 1 per group 1 per class 2 per group 1 set per group

1 roll per class 1 set per group

Things to do Make sure there is enough space for the groups to perform the two experiments given below.

Safety Precautions Not Applicable.

SESSION Link to known information/previous activity [In the previous activity demonstrating Newton’s second law, we saw that Force = mass x acceleration. In this section, we will see that any force causing an action is opposed by an equal and opposite force causing a reaction to the action.

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Procedure Divide students into groups, and have each group complete both 5.3a and 5.3b.

SESSION 6.3a Balloon and straw

FIGURE 6 – BALLOON AND STRAW ACTIVITY Take a thread of 5 meters and insert it through the straw as shown in the figure above. Ask two students from each group to hold the thread at each end, horizontally. Inflate a balloon and tie it tight at the neck with string so that air does not escape. Fix the inflated balloon to the straw using cello tape. Remove the string from the neck of the balloon and see what happens.

SESSION 6.3b Tin and water

FIGURE 7 – TIN CAN MODEL Take Tin 1 and fill it with water holding it under the water level in the basin. Now hold it up with the string and see it move very slowly as water leaks out through the holes Repeat the experiment with Tin 2 and Tin 3 and observe what happens.

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UNDERSTANDING THE ACTIVITY 6.4a Balloon and straw Leading questions 1. What happened to the balloon and straw as you released the air?

2. Why did the balloon and straw move along the thread?

Discussion and Explanation  When the string is untied, air starts rushing out of the balloon.

This causes the walls of the balloon to collapse, which in turn exerts force on the escaping air.  This escaping air exerted a force on the balloon – but the force was exerted in the opposite direction. This opposing force causes the balloon to move in the opposite direction from the escaping air along the string.

6.4b Tin and water Leading questions 1. What happened to each of the 3 tins when they were filled with water and lifted above the water level?

2. Which tin rotated the fastest?

Discussion and Explanation  We have seen that for Tin 1 the movement is very slight. Tin 2 (with 2 tangentially pierced holes) rotates at a good speed. Tin 3 (with 4 holes) rotates faster than Tin 2.  In each case, the movement slows down as the water level in the tin decreases.  The water rushing out of the hole (action) creates a force in the opposite direction (reaction). A pair of diametrically opposite tangential holes leads to the rotation of the can. This is because the two tangential holes ensure the flow of water in opposite directions. Water rushing out of the tin was the action force and the rotation of the tin was the reaction force.  To every action there is an opposed, equal reaction.  It doesn’t matter which force we call action and which we call reaction. The important thing is that they are parts of a single interaction and that neither force exists without the other.  The two experiments that we have performed demonstrate Newton’s third law, which states that every action exists with an equal and opposite reaction.

KEY MESSAGES 

Newton’s third law states that every action exists with an equal and opposite reaction.

LEARNING CHECK In the following examples, give students the action force and have them respond with the appropriate reaction force:

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In the following examples, ask students to identify the action force and reaction force:

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59 How is an action/reaction force pair different from forces at equilibrium (in balance)? They both describe “equal and opposite” forces!

(Answer: Forces in equilibrium act on the same object to cancel each other out. Action and reaction forces are equal and opposite, but they act on different objects, so they can’t cancel each other out!)

TRY IT YOURSELF The next time you are sitting in a car while it turns, notice how your body moves. This is because of inertia!

Stand on roller skates or a skateboard without moving, and throw some balls. Do you start moving? In what direction? What forces are involved?

Take a small ball and set it in front of you. Start it rolling. Try pushing it in its direction of motion, pushing it opposite to its direction of motion, and pushing it sideways from its direction of motion. What happens?

INTERESTING INFORMATION Sir Isaac Newton (1642-1727) was by many standards the most important figure in the development of modern science. Many would credit he and Einstein with being the most original thinkers in that development.

Newton's accomplishments were of astonishingly broad scope. He made fundamental contributions in physics, astronomy and in calculus. This led the poet Alexander Pope was moved to write the lines Nature and Nature's laws lay hid in night; God said, Let Newton be! and all was light Kepler had proposed three Laws of Planetary Motion. These applied only to the motion of the planets; they said nothing about any other motion in the universe.

Newton demonstrated that the motion of objects on Earth could be described by three new Laws of motion, and then he went on to show that Kepler's three Laws of Planetary Motion were but special cases of Newton's three Laws!11

WEB RESOURCES http://hyperphysics.phy-astr.gsu.edu/hbase/newt.html http://www.physics.montana.edu/physed/misconceptions/forces/forces.html (a list of common misconceptions about forces and Newton’s Laws) http://ltlphysics.blogspot.in/2013/04/common-misconceptions-when-using.html (blog post about teaching Newton’s Third Law) http://www.cpo.com/ipcres/pdfs/unit1/Ch3Sec3.pdf (fabulous, illustrated explanation of Newton’s Third Law) http://howthingsfly.si.edu/flight-dynamics/newton%E2%80%99s-laws-motion (A Smithsonian Museum website that explains Newton’s Laws of Motion in a very entertaining way) http://facstaff.gpc.edu/~pgore/PhysicalScience/forces-motion.html (textbook-like format, but includes several good hands-on activities) http://www.physicsclassroom.com/class/circles/u6l1d.cfm (circular motion) Agastya International Foundation. For Internal Circulation only.

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60 http://phys.udallas.edu/C3P/Preconceptions.pdf (sections 0-4 are most relevant)

VOCABULARY 1) Inertia of rest – The property that states that an object at rest remains at rest if no external force acts on it 2) Inertia of motion – The property that states that an object in motion remains in motion with the same velocity if no external force acts on it 3) Newton’s First Law – The law of inertia, stating that an object at rest remains at rest, and an object in motion remains in motion, unless acted upon by an external force 4) Newton’s Second Law – The law that states that the magnitude of a force is equal to the magnitude of the acceleration it causes multiplied by the mass it acts on 5) Newton’s Third Law – The property that states that every action force exists simultaneously with an equal and opposite reaction force

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LEARNING CHECK In the following activities, determine whether the force applied is a pushing or a pulling force, and check the appropriate box.

1

Activity Sucking juice

2

Erasing/Rubbing black board

3

Magnet attracting nails

4

Fruits falling from trees

5

Lifting weight

Diagram

Push

(Answers: 1. Pull; 2.Push; 3.Pull; 4.Pull; 5.Both (Pull by arms and push by feet).

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Pull

Both

62

LEARNING CHECK Mark the object as at rest or in motion: Object condition The hands of a wall clock A cell phone kept on the table The wings of a bird while flying The branches of a tree on a windy day A car parked on the side of the road An apple falling from a tree A man sitting on a bus Blood circulation in a person sitting on a bench

At rest

In motion

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LEARNING CHECK Mark the objects given in the table below as being at rest or in motion: Object A flying bird

A man on a bus

The hands of a clock

A boat on a river

Object Condition The wings of a bird while flying, relative to someone standing on the ground The right wing of a bird with respect to its left wing The wings of the bird with respect to its beak A man sitting in a bus with respect to a man standing at the side of the road A man sitting in a bus with respect to another person on the bus The seconds hand of a wall clock with respect to the clock dial The hours hand of a wall clock with respect to the minutes hand A boat travelling down a river with respect to a person standing on the bank A steam-powered boat travelling down a river with respect to a person floating down the river on a log

At rest

In motion

Note to Instructor: When birds fly, their wings move together, so the left and right wing will be at rest relative to each other; both wings are in motion with respect to the bird’s beak

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Learning check for different types of motion Distribute the observation sheet given below. Ask the students to identify the types of motion and tick the appropriate box(es).

Observation sheet for learning check on types of motion Motion

Translatory

Oscillatory

Rotatory

1

2

3

4

5

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7

8

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LEARNING CHECK Draw the below diagram on a black board/white board and give the following problem to the learners.

An object starts from Point A, travels on a circular path, and returns to the starting point A. Measure the distance and displacement of the object for the following different paths: 1. A to B 2. A to C 3. A to D 4. A to E 5. A to A 6. C to E

Hint 1:For distance, run the thread from A to B along the circle line, mark the end, and measure the length using a meter stick. For displacement, draw a straight line from A to B and measure its length using the meter stick. Repeat the same procedure for the other points.

Hint 2: The displacement from A to A is zero.

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WORKSHEET 1 – Speed Group activity - Speed Place the marble at the top end of the curved groove and release it. Measure the time of its journey from the top of the board to the base. Repeat the trail three times and find the average time (t). Measure the distance (s) of the curved path from top to the bottom with the help of thread and scale. Calculate s/t Distance s (m)

Time t (s)

Average time (t)

Time t2 (s)

Speed v= s/t (m/s)

t1 = t2 = t3=

WORKSHEET 2 – Velocity Group activity - Velocity Place the marble at the top end of the straight groove and release it. Measure the time of its journey from the top of the board to the base. Repeat the trail three times and find the average time (t). Measure the distance (s) of the path from top to the bottom with the help of thread and scale. Calculate s/t Distance s (m)

Time t (s)

Average time (t)

Time t2 (s)

Velocity v= s/t (m/s)

t1 = t2 = t3 =

WORKSHEET 3 - Acceleration

Trial

Distance s (m)

Time t1 (s)

Average time Acceleration a (2s/t2)

1 2 3

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WORKSHEET 4 – Newton’s second law

Trial

Distance s (m)

Time t1 (s)

Average time Acceleration a (2s/t2)

Mass m (kg)

1 2 3

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F = ma

69

LEARNING CHECK In the following examples, give students the action force and have them respond with the appropriate reaction force:

In the following examples, ask students to identify the action force and reaction force:

How is an action/reaction force pair different from forces at equilibrium (in balance)? They both describe “equal and opposite” forces!

(Answer: Forces in equilibrium act on the same object to cancel each other out. Action and reaction forces are equal and opposite, but they act on different objects, so they can’t cancel each other out!)

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REFERENCES 1Kurtus,

Ron. “School for Champions.” 28 October 2007. http://www.school-forchampions.com/science/motion.htm.

2http://www.windows2universe.org/the_universe/uts/log.jpg 3 “Rotational Motion.” Wonder WhizKids.Wiki Kids Ltd. 2013.http://www.wonderwhizkids.com/index.php/physics/mechanics/rotational-motion.

4http://en.wikipedia.org/wiki/Wilberforce_pendulum 5 “Speed and Velocity.” The Physics Classroom.2013.http://www.physicsclassroom.com/class/1dkin/u1l1d.cfm.

6 “Physics Problems: Kinematics.” Solvephysics.com. 2009. http://www.solvephysics.com/kinematics_part1.shtml.

7 “Average vs. Instantaneous Speed.” The Physics Classroom.2013.http://www.physicsclassroom.com/mmedia/kinema/trip.cfm.

8 “What is Acceleration?”.Math and Science Activity Center. EdInformatics.com. 1999. http://www.edinformatics.com/math_science/acceleration.htm.

9http://www.grc.nasa.gov/WWW/K-12/BGA/Sheri/newton%27s_first_law_act.htm 10http://www.physicsclassroom.com/class/newtlaws/u2l3a.cfm 11http://csep10.phys.utk.edu/astr161/lect/history/newton.html

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