thequarkyteacher.files.wordpress.com · web view2020. 7. 21. · air resistance. the force acting...

Edexcel ScienceiGCSE Physics

A.Fundamentals of Forces2019-2020

Name:________________Physics Teacher:______________

House CG Test Score

Year 9

Specification Checklist

1.01 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2

(m/s2), newton (N), second (s) and newton/kilogram (N/kg)

1.11 describe the effects of forces between bodies such as changes in speed, shape or

direction

1.12 identify different types of force such as gravitational or electrostatic

1.13 understand how vector quantities differ from scalar quantities

1.14 understand that force is a vector quantity

1.15 calculate the resultant force of forces that act along a line

1.16 know that friction is a force that opposes motion

1.18 know and use the relationship between weight, mass and gravitational field strength:

weight = mass × gravitational field strength

W = m × g

1.22 practical: investigate how extension varies with applied force for helical springs,

metal wires and rubber bands

1.23 know that the initial linear region of a force-extension graph is associated with

Hooke’s law

1.24 describe elastic behaviour as the ability of a material to recover its original shape

after the forces causing deformation have been removed

1.31 know that the weight of a body acts through its centre of gravity

Fundamentals of Forces – Science (Physics) 2

Key Words

Key Word Image Definition

Air Resistance The Force acting against movement in air. Caused by collision with air particles.

Compression A force that squashes an object, making it shorter.

Centre of Gravity

The point in an object where weight acts downwards from.

Elastic A material that will return to its original shape after being stretched or compressed.

Electrostatic The force of attraction or repulsion between positive and negative charges.

Extension The amount an object has been stretched by.

Friction A force that acts in the opposite direction to the motion.

GradientThe steepness of a line. Calculated by

Change∈y valueChange∈x value .

Gravitational force.

This is called Weight. Gravity is a field that causes objects to weigh something.

Limit of Proportionality

The point where a material no longer obeys Hooke’s Law.

Mass The amount of matter something is made from. This does not change no matter where you are in the universe.

Newton The unit for force. [N]

Resultant Force

The overall force remaining after you have added and subtracted all the forces from each other. Also known as net or unbalanced force

Reaction Force The force acting back against an electrostatic push.

Scalar A quantity with only magnitude (size). For example, speed.

Tension The force pulling something to stretch it.

Upthrust An upward force on an object in a liquid or gas that gives it buoyancy, helping it float.

Vector Something with both direction and magnitude. For example, velocity

Weight The downward force on an object due to gravity, pulling it towards the earth. This can be different on different planets.


Lesson 1: What are Forces?

Learning Outcomes:

1. State the Safety Rules for the Lab and Classroom Rules2. Describe the effect Forces have on an object3. Identify the different types of Forces.

Lab SafetyUse your previous Science knowledge to analyse the scene below.

Circle Hazard in Red Circle Good Practice in Green

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Task: What do you know about Forces?


On the mind map below can you add everything you already know about Forces? Be ready to share your ideas with the class.

Types of Forces

Key Ideas

1. Forces can be described as contact or non-contact2. Weight is the Force that acts on an object due to gravity.

A1: Identifying Forces


FORCES

Health and Safety Check!

I will wear goggles around the springs

In this investigation you are going to look at aCarousel of different Forces.

At each Station you should:

1. Sketch what you see2. Identify the different types of forces in the set up3. Label them on your sketch

Remember the Lab Safety Rules you have just learnt!

Station 1

Sketch

The Forces I can see are:

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Station 2

Sketch



……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Station 3

Sketch


……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Worksheet – Identifying Forces

Can you label the forces in the diagrams below? Use the forces you have learnt on page 6.


Lesson 2: Balanced and Unbalanced Forces

Identifying Forces


Score /11

How many different forces can you identify in the image below? Label the on the picture.


Learning Outcomes:

1. Describe the difference between a vector and a scalar quantity.2. Sketch diagrams to illustrate balanced an unbalanced force.3. Calculate the resultant force on an object and explain how this can result in a

change of speed, direction or shape.

Balanced and Unbalanced Forces (Resultant Forces)

Key Ideas

1. Force is measured in Newton’s. 2. When forces are balanced the object will move at a constant speed (already moving)

or will not move at all (remain stationary)3. When forces are unbalanced the object will change shape, speed or direction. 4. When forces are balanced the resultant force is zero. 5. When forces are unbalanced the resultant for is non-zero.


Vectors vs. Scalars

Examples

Vector Scalar

Key Ideas

1. Scalars are quantities that only have magnitude (size).2. Vectors are quantities that have magnitude (size) and direction. 3. Force is a vector quantity. 4. We can represent Force as an arrow on a diagram to illustrate direction and size

(length).

Worked Examples – Resultant Force

What is the resultant force on the following objects? Represent it on the second trolley.


Resultant force

55N

Worksheet – Calculating the Resultant Force

In each of the examples below calculate the resultant force and state its direction.

1. 2.

Resultant Force = ……. ………... Resultant Force = ……. ………...

3. 4.


5. 6.


7. 8.



4N 10N

92N 110N600N 124N

25N 13N

125N

72N

5.2N

11.3N

50N 50N

103N

34N

64N 22N

60N

60N

Lesson 3: Friction

Resultant ForceUse your knowledge from the previous lesson to answer the questions below:


Learning Outcomes:

1. Describe Friction as the force that acts opposite the direction of motion2. Carry out an investigation to look at the relationship between mass and friction. 3. Explain how you can use the concept of balanced forces to measure friction.

What is Friction?

Key Ideas

1. Friction is a Force caused by two surfaces rubbing against each other. 2. Friction can generate heat.3. Friction always acts opposite the direction of motion of an object. 4. Friction can be affected by mass, surface area and surface type.


A2: Investigating Friction

In this investigation you are to investigate the effectsof mass on friction.

What other factors can affect friction?

1. 2.

These factors must be kept the same during the investigation.

Method

1. Set up your apparatus as shown in the diagram

2. Apply 200g to your wooden block. 3. Pull slowly on the newton meter until the

block is at a constant speed.4. Take reading from the Newtonmeter.5. Repeat reading to improve accuracy

and reliability6. Repeat steps 2-5 for different masses

(200g increments)

Results

Mass [kg]Force [N]

Average Force [N]

Attempt 1 Attempt 2 Attempt 3

0.2

0.4

0.6

0.8

1.0

1.2



I will be careful when handling masses

mass

Now plot your results in a graph below (Mass on the x-axis, Force on the y-axis)

Use your results to answer the following questions:

1. Using the idea of balanced forces, explain why the ‘Force [N]’ on your graph is the

same size as the friction on your block.

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

2. Describe the relationship between mass and friction.

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

3. What challenges did you have with your investigation?

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

4. What steps could you have taken to improve the accuracy of your results?

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………


Graph Checklist

Axes Labels (inc. units)

AppropriateScale

Points Plotted

Line of BestFit

Lesson 4: Weight and Mass

Knowledge and Understanding QuizUse the knowledge you have gained in the previous 3 lessons to answer the following questions:

1. In what direction does Friction act?

……………………………………………………………… (1)

2. What is the resultant force on an object that has 10N pulling it right and 35N pulling it left?

………………………………………………………………………………………… (2)

3. Label the forces on the diagram below:

(4)

4. Give 3 ways to decrease friction on an object.

…………………………………………………………………………………………

…………………………………………………………………………………………

………………………………………………………………………………………… (3)

Score [ /10]


Learning Outcomes:

1. Describe the difference between weight and mass. 2. Use the equation

Weight=mass×gto calculate the weight of an object. 3. Define the Centre of Gravity as the point through which weight acts.

Weight and Mass

Key Ideas

1. Weight is a force caused by the Gravitational Field on Earth. It can change on other planets (unlike mass)

2. Weight, mass and g are linked in the following equation:Weight=Mass×g

3. On Earth, g=10N /kg

Worked Examples

1. What is the weight of an object which has a mass of 25kg?

2. If the average man has a weight of 750N. What is the average mass of a man?

Worksheet – Weight, Mass and g


Complete the questions below using the equation you have just learnt. You must show all of your working [equation, substitution, solution and units]

1. How much does a 55kg human weigh?

…………………..

2. What is the weight on a 22.5kg suitcase on earth?

…………………..

3. Dumbo the elephant measures his mass to be 700kg. How much does he weigh?

…………………..

4. What is the mass of a Dictionary with a Weight of 12N?

…………………..

5. What is mass of an object which weighs 6520N?

…………………..

6. A beaker of water is put on a balance and is found to have a mass of 600g. What does it weigh?

…………………..

7. On Pluto, an object with a mass of 150kg will weigh 90N.a. What is the value of g on Pluto?

…………………..

b. What would the weight of a 900kg truck be on Pluto?

…………………..

Use the table to help you answer the following questions:


…………………..

8. What is the voltage when 1000J of energy is transferred through a circuit with a charge of 3C?

9. What would a 20kg suitcase weigh on the moon?

…………………..

10. What would the mass of an object be if it weighed 100N on Jupiter?

…………………..

11. How much less would you weigh on Mercury than on Earth if you had a mass of 65kg?

…………………..

12. What would a 600g bag of sugar weigh on Uranus?

…………………..

13. What is the mass of a car that weighs 3500N on Venus?

…………………..14. What would a 1 tonne elephant weigh on:

a. Jupiter

…………………..b. Neptune

Centre of Gravity


Key Ideas

1. The Weight of an object acts through its Centre of Gravity.2. If you support a shape at its Centre of Gravity it will balance3. It is sometimes called the Centre of Mass.

Where would you expect to find the Centre of Gravity of the following Regular Shapes?

Add an arrow to each shape to show where weight acts. Use a ruler.

A3: Centre of Gravity



I will be aware that the pin is at eye height

In this investigation you are going to be finding theCentre of Gravity of an irregular object.

Make sure to illustrate your results on the next page!

Method

1. Set up your apparatus as shown in the diagram.

2. Hang your irregular shape by one of the holes. 3. Hang the plumb line off the same spot.4. Mark on crosses to show where the plumb line

passes through5. Join up crosses6. Repeat steps 2-5 for another hole in the shape7. Where the lines intersect is the centre of gravity.8. Test this by balancing the shape on your finger!

Method illustrated:

Results


Draw around your shape and show how you found the Centre of Gravity.

1. How did you check that you had found the Centre of Gravity?

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

2. What would be the benefit of drawing another line on the shape using the same

method?

……………………………………………………………………………………………

……………………………………………………………………………………………

……………………………………………………………………………………………

Lesson 5: Hooke’s Law


Weight, Mass and gCan you answer the following questions using your knowledge from last lesson?

1. What is the weight of an object with a mass of 55kg?

……………………….[3]

2. What is the weight of an object with a mass of 450g?

……………………….[3]

3. What is the mass of an object that weighs 23N?

……………………….[3]

4. On a far distance planet a 600kg object weighs 150N. What is the value of g on this planet?

……………………….[3]

[Score /12]


Learning Outcomes:

1. State Hooke’s Law and represent it on a Force-Extension Graph2. Describe a practical to investigate the relationship between force and extension

of a helical spring3. Define the ‘Limit of Proportionality’

A4: Investigating Hooke’s Law

In this investigation you are going to be measuring how extension varies with force applied.

Answer the questions below before you begin theinvestigation!

1. You will be given the value of your mass in kg. How do you turn this into a force [N]?

2. You will have to measure the extension of your spring rather than the length. Draw a diagram below and explain how to measure extension.

Method


2. Measure the length of your spring without any hanging masses.

3. Hang a mass of 100g on the spring4. Measure the new length of the spring5. Calculate the extension of the spring6. Repeat steps 3-5 for increasing the mass

in increments of 100g7. Take note of your results in the table.

Original Length of Spring =



I will wear goggles when using springs

Results

Mass [g] Mass [kg] Force [N] Extension [cm]

0

100

200

300

400

500

600

700

800

Now plot your results below (extension on the x-axis, Force on the y-axis)

Describe the relationship between force and extension.

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………


Graph Checklist


AppropriateScale

Points Plotted

Line of BestFit

……………………………………………………………………………………………………………

Hooke’s Law

Key Ideas

1. Hooke’s Law: extension is directly proportional to the force applied. 2. It can be represented as a straight line through the origin on a Force-Extension

Graph3. We call the point when an object stops obeying Hooke’s Law the limit of

proportionality.


Lesson 6: Elastic Behaviour

Knowledge and Understanding QuizUse the knowledge you have gained in the previous 5 lessons to answer the following questions:

1. What is the mass of an object that weighs 152N?

……………………………………………………………… (2)

2. State Hooke’s Law

…………………………………………………………………………………………………………………………………………………………………………………… (1)

3. Represent Hooke’s Law on a Force-extension graph:

(3)

4. What is a vector quantity?

…………………………………………………………………………………………

………………………………………………………………………………………… (2)

5. A car is travelling along the motorway at 60mph. What can you say about the Forces

on the car?

…………………………………………………………………………………………

………………………………………………………………………………………… (2)

Score [ /10]

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………


Learning Outcomes:

1. Define the terms ‘loading’ and ‘unloading’ 2. Describe elastic behaviour as the ability of a material to recover its original

shape after being stretched. 3. Carry out an investigation to test whether or not different materials behave

elastically.

Elastic Behaviour

Key Ideas

1. Elastic behaviour is the ability of a material to recover its original shape after the forces causing deformation have been removed.

2. We say an object has past it’s elastic limit when it stops behaving elastically (will not return to it’s original shape.


A5: Elastic Behaviour

In this investigation you are going to be measuring how extension varies with Force applied.

Method


2. Mark your elastic band in two places à 3. Measure the distance between the points

on your elastic band* without any hanging masses.

4. Hang a mass of 100g on the elastic band5. Measure the new length of the elastic band6. Calculate the extension of the spring7. Repeat steps 3-5 for increasing the mass

in increments of 100gDo not take masses off in betweenreadings!

8. Now unload the elastic band one massat a time

9. Measure the extension of the elastic bandeach time.

10. Repeat with Strawberry Lace



I will wear goggles when using springs

I will not consume theequipment

Elastic band/lace

100g masses

Results – Elastic Band

Mass [g] Mass [kg] Force [N]Extension

[cm] Loading

Extension [cm]

Unloading

0

100

200

300

400

500

Now plot your results below (extension on the x-axis, Force on the y-axis) Plot Loading and Unloading in different colours!

Is the elastic band behaving elastically? Explain your answer.

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Does the Elastic Band obey Hooke’s Law? ………………………..


Graph Checklist

Title


AppropriateScale

Points Plotted

Line of BestFit

Results – Strawberry Lace

Mass [g] Mass [kg] Force [N]Extension

[cm] Loading

Extension [cm]

Unloading

0

20

40

60

80

Now plot your results below (extension on the x-axis, Force on the y-axis) Plot Loading and Unloading in different colours!

Is the strawberry lace behaving elastically? Explain your answer.

……………………………………………………………………………………………………………

……………………………………………………………………………………………………………

Does the strawberry lace obey Hooke’s Law? ………………………..


Graph Checklist

Title


AppropriateScale

Points Plotted

Line of BestFit

Stretch Activity – Resultant Force in 2D

Forces do not always act along one line. Sometimes the Resultant force ends up at an angle. Watch the following video and make notes below on how to use a scale drawing to add vectors in 2D.

https://www.youtube.com/watch?v=JRsFx69UdDc

Worksheet – Vectors in 2D

Use what you have learnt to find the resultant force in the following examples.

1. What is the resultant force of 50N acting north and 25 N acting east? Give a bearing to represent the final direction of the resultant force.

2. What is the resultant force of 300N acting north and 400 N acting east? Give a bearing to represent the final direction of the resultant force.


https://www.youtube.com/watch?v=JRsFx69UdDc

3. What is the resultant force of 60N acting south and 60 N acting east? Give a bearing to represent the final direction of the resultant force.


Fundamentals of Forces

Past Paper Questions

Q1.

A student wants to use a weighing scale to find the weight of her school bag.

She has a weighing scale marked in kilograms instead of Newtons.

The weighing scale is not working properly.

With nothing hanging from it, the weighing scale shows 1.5 kg.


(a) What is the weight of a 1.5 kg mass?(1)

Weight = ........................................................... N

(b) The student decides to check the weighing scale.She has no accurate weights.Instead, she puts some tins of beans in a plastic bag and hangs it from the scale.


Her readings are shown in the table.


(i) Draw a graph to show how the scale reading varies with the number of tins ofbeans.

(5)

(ii) Circle the anomalous point on your graph.(1)


(c) The student notices that the label on each tin says 'contains 0.4 kg of beans'.She remembers that six tins of beans gave a scale reading of 3.9 kg.

She hangs her school bag from the weighing scale.The scale reading is 5.0 kg.She also concludes that her school bag must have a mass of exactly 3.5 kg.Suggest reasons why the student's conclusions might be incorrect.

(4) .............................................................................................................................................

.............................................................................................................................................

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(Total for question = 11 marks)


Q2.

A student plans to measure the thickness of a sheet of paper with a ruler.

(a) Explain why it is difficult to measure the thickness of a single piece of paper witha ruler.

(2) .............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(b) The student puts a pile of 400 sheets of paper on a table.He uses a ruler to measure the height of the pile.

The student records the thickness of the pile as 4.1 cm.(i) This means that the thickness of one piece of paper is about

(1)

A 1 cm

B 1 mm

C 0.1 mm

D 0.01 mm

(ii) Suggest two reasons why the student's value for the thickness of the pile maybe inaccurate.

(2)1.................................................................................................................................................

...................................................................................................................................................


...................................................................................................................................................

2.................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

(c) The student folds the sheet of paper to make a paper aeroplane.He throws the paper aeroplane into the air and it flies at a constant velocity.(i) Explain why the forces on the paper aeroplane must be balanced.

(2)...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

...................................................................................................................................................

(ii) The diagram shows the paper aeroplane as it moves at a constant velocitytowards the right and slightly downwards.

Add labelled arrows to the diagram to show the directions of the forces of

weight lift drag (3)

(iii) As it flies, the paper aeroplane loses gravitational potential energy.What happens to this energy?

(1)...................................................................................................................................................

...................................................................................................................................................



Q3.

A student makes chains of elastic bands by joining them together with paperclips.

He uses a newtonmeter to stretch each chain along a metre rule, as shown in photograph A.

For each chain, he records

the number of elastic bands the length when the tension is 2 N the length when the tension is 1 N

Then he calculates the difference in length for each chain.

(a) (i) Complete the table by calculating the missing value.(1)


(ii) Use the grid to plot a graph to show the relationship between the number ofelastic bands and the difference in length.

(5)

(iii) Describe your line of best fit.(2)

.............................................................................................................................................

.............................................................................................................................................


(b) Photograph B shows a paperclip in one of the chains against the same metre rule.

Use photograph B to estimate the length of this paperclip.(2)

Length = ........................................................... cm

(c) Look again at photograph A.Suggest two ways that the student could improve his measuring technique.

(2)1 ................................................................................................................................................

.............................................................................................................................................

2 ................................................................................................................................................

.............................................................................................................................................



Q4.

A student investigates how the extension of a spring varies when he hangs different loads from it.

(a) Write a plan for the student's investigation.

Your plan should include details of how the student can make accurate measurements.

You may add to the diagram to help your answer.(5)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

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(b) The student finds that the spring obeys Hooke's law.

Draw a graph on the axes to show the Hooke's law relationship.

Label the axes.(3)

(c) The student concludes that the spring shows elastic behaviour.

Explain what is meant by the term elastic behaviour.(2)

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

.............................................................................................................................................

(Total for Question = 10 marks)


Q5.

(a) State the similarity and the difference between scalars and vectors.(2)

similarity

.............................................................................................................................................

.............................................................................................................................................

difference

.............................................................................................................................................

.............................................................................................................................................

(b) Complete the table by ticking ( ) the correct boxes to show whether each quantity is a scalar or a vector.

The first one has been done for you.(3)

(Total for Question = 5 marks)


Fundamentals of Forces

Spec Point Notes

Fundamentals of Forces Specification Notes


1.01 use the following units: kilogram (kg), metre (m), metre/second (m/s), metre/second2 (m/s2), newton (N), second (s) and newton/kilogram (N/kg)

1.11 describe the effects of forces between bodies such as changes in speed, shape or direction

1.12 identify different types of force such as gravitational or electrostatic

Gravitational, weight, friction, electrostatic, air resistance (drag), tension (force in a spring), upthrust, lift, thurst

1.13 understand how vector quantities differ from scalar quantities

Scalars are quantities that only have magnitude (size) Vectors are quantities that have magnitude (size) and direction

1.14 understand that force is a vector quantity


1.15 calculate the resultant force of forces that act along a line

1.16 know that friction is a force that opposes motion

1.18 know and use the relationship between weight, mass and gravitational field strength:

Weight [Newtons] = mass [kilograms] × gravitational field strength [10N/kg]

W = m × g1.22 practical: investigate how extension varies with applied force for helical springs,

metal wires and rubber bands

1.23 know that the initial linear region of a force-extension graph is associated with Hooke’s law


1.24 describe elastic behaviour as the ability of a material to recover its original shape after the forces causing deformation have been removed

1.31 know that the weight of a body acts through its centre of gravity


Weight

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