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Primary Science · Year 5Chapter 9 · Gravity, friction and resistance
Year 5 · Chapter 9

Gravity, friction and resistance

By the end of this chapter you will be able to

  • Explain that gravity pulls unsupported objects towards the Earth
  • Describe how air resistance slows a falling object, and how a larger surface catches more air
  • Describe how water resistance slows an object moving through water, and how a streamlined shape helps
  • Explain that friction acts between surfaces that rub, and against the motion
  • Use a fair test to compare fall times, and read a bar chart of the results

You should already know

  • Pushes, pulls and contact forces, and friction (Year 3 Science, Chapter 9)
  • Air resistance and water resistance, from a fair test with paper shapes (Year 3 Science, Chapter 9)

Where this leads

  • Levers, pulleys and gears, which make forces easier to use (Year 5 Science, Chapter 10)
  • Working scientifically, planning and reporting (Year 5 Science, Chapter 1)

National Curriculum for England, Key Stage 2 science, Year 5. Content: F1 explain that unsupported objects fall towards the Earth because of the force of gravity acting between the Earth and the falling object, F2 identify the effects of air resistance, water resistance and friction that act between moving surfaces.

Exercise P  Do you remember?

1
FName the type of force that slows down a moving object when two surfaces rub together. Write the word.
2
FIs a push a force? Write yes or no.
3
FWhich kind of material is a sheet of paper that is crumpled into a ball: the same material, or a different one? Write the words.
4
FWhich is a fair test: changing only one thing at a time, or changing everything at once? Write the words.
5
FWrite the word for the shape of a parachute that catches a lot of air, such as a large flat one: flat or streamlined? Write the word.
9.1

Gravity pulls things down

Year 5
F1: explain that unsupported objects fall towards the Earth because of the force of gravity acting between the Earth and the falling object
Video lesson: Gravity pulls things downComing soon
Story. Ruby drops a pencil, and it falls to the floor. “Why does it always fall down, and never up?” she asks. Her teacher says: “Gravity is a force. It pulls objects towards the Earth.”

Gravity is a force that pulls objects towards the Earth. It acts between the Earth and every object on it, even when the two objects are not touching.

An object that is not held up, or unsupported, falls towards the Earth because of gravity. This is why things fall when you drop them.

Gravity pulls downwards, towards the centre of the Earth. It is a force that acts at a distance, so it does not need contact.

gravitygravity still actsgravity pulls every object towards the Earthheldfalling
A ball held above the ground, and a ball falling. Gravity pulls both towards the Earth, downwards.

Key ideas

  • Gravity is a force that pulls objects towards the Earth.
  • An unsupported object falls towards the Earth because of gravity.
  • Gravity acts downwards, and it acts at a distance.
  • A supported object, such as a book on a table, does not fall, because the table pushes it up.
Worked example 9.1.1
What force makes a dropped pencil fall to the floor? Write the word.

Method. Think about what pulls the pencil down.

  1. Think about the pencil. The pencil falls because it is unsupported.
    unsupported
  2. Name the force. The force that pulls it down is gravity.
    gravity
  3. Write the answer.
    gravity

Check. Gravity acts between the Earth and the pencil. ✓

Worked example 9.1.2
In which direction does gravity pull a falling ball? Write the word: up or down.

Method. Think about where the Earth is.

  1. Think about the Earth. The Earth is below the ball, at the centre of the Earth.
    below
  2. Choose the word. So gravity pulls the ball down.
    down
  3. Write the answer.
    down

Check. Gravity pulls towards the centre of the Earth. ✓

Worked example 9.1.3
Does a book on a table fall? Write yes or no.

Method. Think about what supports the book.

  1. Think about the table. The table pushes the book up, so the book is supported.
    supported
  2. Decide. A supported object does not fall, so the answer is no.
    no
  3. Write the answer.
    no

Check. The table is holding the book up. ✓

Watch out

Watch out: gravity pulls an object towards the Earth even when it is not touching the Earth. It acts at a distance.

Try it (with your teacher or a grown-up). Hold a pencil, a small ball and a sheet of paper, one at a time, at the same height above a soft rug. Let each one go, with your teacher watching. Which ones fall? Which force pulled them down?

Exam tip

Grown-up tip. Ask: “Which force pulled the object down? What would happen if you held it up?” Keep the drop low and on a soft surface.

Exercise 9A  Gravity pulls things down

1
FWhat is the force that pulls objects towards the Earth? Write the word.
2
FWhy does an unsupported object fall towards the Earth? Write the word.
3
FIn which direction does gravity pull a falling object? Write the word: up or down.
4
FDoes a book on a table fall to the floor? Write yes or no.
5
FFill in the gap: gravity is a force that acts at a ___. Write one word.
6
PSLook at the picture in section 9.1. Which way does the gravity arrow point on the falling ball? Write the word: up or down.
gravitygravity still actsgravity pulls every object towards the Earthheldfalling
7
PSLook at the picture in section 9.1. How many balls are shown with a gravity arrow? Write the number.
gravitygravity still actsgravity pulls every object towards the Earthheldfalling
8
PSPriya says: “Gravity only pulls heavy objects.” Is Priya right? Write yes or no.
9
PSWorking scientifically. Predict what happens. Predict what will happen to a pencil if you hold it still in the air, and then let go. Write one word.
10
RExplain why a ball falls when you let go of it. Write one sentence.
11
RExplain why a book stays still on a table, even though gravity pulls it down. Write one sentence.
9.2

Air resistance

Year 5
F2: identify the effects of air resistance that act between moving things and the air
Video lesson: Air resistanceComing soon
Story. Mo drops two parachutes from the same height in the playground. One is wide, and one is small. “The wide one floats down so slowly,” he says. “Why is it so different?” His teacher says: “Air pushes against the wide parachute. That is air resistance.”

Air resistance is a force that acts against things moving through air. It pushes against the motion, so it slows the thing down.

A larger flat surface catches more air, so it has more air resistance. A small, streamlined shape has less air resistance, and it falls faster.

large parachutemuch air resistance: falls slowlysmall parachuteless air resistance: falls quickly
A large parachute falls slowly because of more air resistance. A small parachute falls quickly.

The table shows the results of a fair test. Each parachute was dropped from the same height, three times, and the time to reach the floor was measured.

Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
mean fall time (seconds)0.00.51.01.52.00.8100 cm²1.0200 cm²1.2300 cm²1.6400 cm²
Bar chart of mean fall time against parachute area: the larger the parachute, the shorter the fall time.

Key ideas

  • Air resistance is a force that slows down moving things in air.
  • Air resistance acts against the motion of a falling object.
  • A larger flat surface has more air resistance, and falls more slowly.
  • A fair test changes only the area of the parachute, and keeps everything else the same.
Worked example 9.2.1
Look at the table in section 9.2. What is the mean fall time for the 200 cm² parachute? Write the number of seconds.

Method. Read the mean for 200 cm².

  1. Read the row. The 200 cm² row has a mean of 10 tenths of a second.
    10 tenths
  2. Write in seconds. Ten tenths of a second is 1.0 second.
    1.0
  3. Write the answer.
    1.0

Check. Check: 10 tenths = 1.0 second. ✓

Watch out. Tenths of a second: 10 tenths is 1.0 second.

Worked example 9.2.2
Which parachute falls most slowly on average: 100 cm² or 400 cm²? Write the area.

Method. Find the longest mean time.

  1. Compare the means. The 100 cm² parachute has a mean of 8 tenths, and the 400 cm² one has 16 tenths.
    8 and 16
  2. Choose the slower. The longer time is 16 tenths, so the 400 cm² parachute falls more slowly.
    400 cm²
  3. Write the answer.
    400 cm²

Check. Larger parachutes fall more slowly in this test. ✓

Worked example 9.2.3
How many tenths of a second faster did the 100 cm² parachute fall than the 400 cm² one? Write the number.

Method. Subtract the smaller time from the larger.

  1. Read the two means. The 400 cm² mean is 16 tenths, and the 100 cm² mean is 8 tenths.
    16 and 8
  2. Subtract. The difference is 16 minus 8, which is 8 tenths.
    16 - 8 = 8
  3. Write the answer.
    8

Check. Check: 8 + 8 = 16. ✓

Watch out

Watch out: the parachute with more air resistance falls more slowly. A heavier object is not what makes it fall faster; here the wider one is the slower one.

Try it (with your teacher or a grown-up). Take two sheets of the same paper. Drop one flat and the other crumpled into a tight ball, from the same height onto a rug. Time each fall three times, and find the mean. Which shape had more air resistance? Stand on the floor, not on a chair.

Exam tip

Grown-up tip. Ask: “Which shape catches more air? Which falls more slowly?” Let your child find the mean of three times.

Exercise 9B  Air resistance

1
FWhat is the name of the force that slows down moving things in air? Write the words.
2
FWhich has more air resistance: a large flat surface or a small streamlined shape? Write the words.
3
FLook at the table in section 9.2. What is the mean time for the 300 cm² parachute, in tenths of a second? Write the number.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
4
PSLook at the table in section 9.2. What is the trial 2 time for the 100 cm² parachute, in tenths of a second? Write the number.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
5
FLook at the table in section 9.2. Work out the mean of the three trials for the 400 cm² parachute. Write the number of tenths.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
6
PSLook at the table in section 9.2. Which parachute falls fastest on average? Write the area.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
7
PSLook at the bar chart in section 9.2. Is the bar for 300 cm² taller or shorter than the bar for 200 cm²? Write the word.
mean fall time (seconds)0.00.51.01.52.00.8100 cm²1.0200 cm²1.2300 cm²1.6400 cm²
8
PSTrue or false: a larger flat parachute has more air resistance than a small one. Write true or false.
9
RExplain why a large parachute falls more slowly than a small one. Write one sentence.
10
PSWorking scientifically. Plan a fair test. Write one thing that must stay the same in a fair test of parachutes. Write one thing.
11
RExplain why we should repeat each parachute drop three times. Write one sentence.
9.3

Water resistance

Year 5
F2: identify the effects of water resistance that act between moving things and the water
Video lesson: Water resistanceComing soon
Story. Tom watches a toy boat sail across a bath. “The pointed boat goes through the water more easily,” he says. “The flat one pushes the water in front of it.” His teacher says: “That push from the water is water resistance.”

Water resistance is a force that acts against things moving through water. Like air resistance, it pushes against the motion and slows the object down.

A flat, blunt shape pushes a lot of water out of the way, so it has more water resistance. A streamlined shape, which is smooth and pointed, lets the water flow past it more easily, so it has less water resistance.

blunt shape: more resistancestreamlined: less resistancewater resistance pushes back against the motion (orange)
A blunt flat shape moved through water has more water resistance than a streamlined shape.
Shape moved through waterWater resistance
a flat, blunt boat shapemore water resistance
a smooth, pointed boat shapeless water resistance

Key ideas

  • Water resistance is a force that slows down moving things in water.
  • A flat, blunt shape has more water resistance than a streamlined shape.
  • Streamlined shapes help things to move through water with less resistance.
  • Water resistance acts against the motion.
Worked example 9.3.1
Which shape has more water resistance: a flat, blunt boat shape, or a smooth, pointed boat shape? Write the words.

Method. Read the table in section 9.3.

  1. Read the table. The flat, blunt shape has more water resistance.
    more water resistance
  2. Choose the shape. So the flat, blunt boat shape has more water resistance.
    a flat, blunt boat shape
  3. Write the answer.
    a flat, blunt boat shape

Check. The flat shape pushes more water out of the way. ✓

Worked example 9.3.2
What is the name of the force that slows down moving things in water? Write the words.

Method. Read the key ideas.

  1. Read the definition. Water resistance is a force that slows down moving things in water.
    slows down moving things
  2. Name the force. The name is water resistance.
    water resistance
  3. Write the answer.
    water resistance

Check. Water resistance acts against the motion. ✓

Worked example 9.3.3
Is a streamlined shape helpful for moving through water? Write yes or no.

Method. Think about the streamlined shape.

  1. Think about the shape. A smooth, pointed shape lets water flow past it more easily.
    flow past
  2. Decide. So a streamlined shape helps it move through water, and the answer is yes.
    yes
  3. Write the answer.
    yes

Check. Streamlined shapes have less water resistance. ✓

Watch out

Watch out: water resistance and air resistance are both forces that push against the motion. They are not the same force, because one acts in air and the other acts in water.

Try it (with your teacher or a grown-up). With your teacher, use a tray of water and two small pieces of card of the same size. Move one flat, sideways, through the water, and the other edge first. Which one feels harder to move? Record your answer, and keep the water in the tray.

Exam tip

Grown-up tip. Ask: “Which one felt harder to push? Why do you think the flat one pushed more water?” Keep the tray on a table, away from the edge.

Exercise 9C  Water resistance

1
FWhat is the name of the force that slows down moving things in water? Write the words.
2
FWhich has more water resistance: a flat, blunt shape or a smooth, pointed shape? Write the words.
3
FWhich shape is streamlined: a smooth, pointed shape or a flat, blunt shape? Write the words.
4
FDoes a streamlined shape have more or less water resistance than a flat shape? Write the word: more or less.
5
FFill in the gap: water resistance acts against the ___ of a moving object. Write one word.
6
PSIs water resistance a force that acts in air? Write yes or no.
7
PSLook at the picture in section 9.3. Which way does the water resistance arrow point, to the left or the right? Write the word.
blunt shape: more resistancestreamlined: less resistancewater resistance pushes back against the motion (orange)
8
PSRuby says: “A boat with a flat front will slide through water more easily than a pointed one.” Is Ruby right? Write yes or no.
9
PSWorking scientifically. Predict, then test. Predict which shape will reach the far side of a tray of water first: the flat card, or the pointed card? Write the word.
10
RExplain why a streamlined boat moves more easily through water. Write one sentence.
11
RExplain why a diver or a fish has a smooth shape. Write one sentence.
9.4

Friction between surfaces that rub

Year 5
F2: identify the effects of friction that act between moving surfaces
Video lesson: Friction between surfaces that rubComing soon
Story. Yusuf rubs his hands together on a cold morning, and they feel warm. “Why do they get warm?” he asks. Mr Patel says: “When two surfaces rub, friction acts between them, and friction makes heat.”

Friction is a force that acts between two surfaces that rub against each other. It acts against the motion, so it slows moving things down.

Friction can be helpful, for example when shoes grip the floor, or when brakes slow a bicycle. Friction can also cause heat, and wear, when moving parts rub together.

Friction is reduced by making surfaces smoother, or by adding oil or grease, so that the surfaces slide more easily.

motionfriction, against the motionfriction acts between two surfaces that rub, and slows the block
A block sliding to the right, with a friction arrow pointing to the left, against the motion.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip

Key ideas

  • Friction acts between two surfaces that rub.
  • Friction acts against the motion of a moving object.
  • Friction can make heat, and it can wear moving parts.
  • Oil or grease reduces friction, so that the surfaces slide more easily.
Worked example 9.4.1
Look at the table in section 9.4. What happens when you rub your hands together? Write the words.

Method. Read the table.

  1. Read the row. The row says rubbing your hands together makes them warm.
    makes them warm
  2. Write the answer. So the friction makes heat.
    friction makes heat
  3. Write the answer.
    friction makes heat

Check. Friction between the hands makes heat. ✓

Worked example 9.4.2
Which direction does friction act, compared with the motion? Write the word: with, or against.

Method. Read the key idea.

  1. Read the key idea. Friction acts against the motion of a moving object.
    against the motion
  2. Choose the word. So the word is against.
    against
  3. Write the answer.
    against

Check. Friction slows moving things down. ✓

Worked example 9.4.3
Is oil on a moving part likely to increase or decrease friction? Write the word.

Method. Read the table.

  1. Read the row. The oil row says less friction, so less wear.
    less friction
  2. Choose the word. So oil decreases friction.
    decrease
  3. Write the answer.
    decrease

Check. Oil lets the surfaces slide more easily. ✓

Watch out

Watch out: friction does not always slow things down in a useful way. Without friction, shoes would slip on the floor and we could not walk safely.

Try it (with your teacher or a grown-up). Rub your hands together for 20 seconds, and feel the warmth. Then rub a smooth plastic lid and a rough piece of paper in the same way, with your teacher. Which one felt warmer? Write your answer, and say which surface was rougher.

Exam tip

Grown-up tip. Ask: “What made your hands warm? Which surface made more friction?” Let your child compare the two surfaces.

Exercise 9D  Friction between surfaces that rub

1
FWhat is the name of the force that acts between two surfaces that rub? Write the word.
2
FWhich way does friction act, compared with the motion of a moving object? Write the word: with or against.
3
FLook at the table in section 9.4. What happens when you rub your hands together? Write the words.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip
4
PSLook at the table in section 9.4. Which example uses oil to reduce friction? Write the words.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip
5
PSLook at the table in section 9.4. Which example uses friction to help us not to slip? Write the words.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip
6
FFill in the gap: friction acts between two surfaces that ___. Write one word.
7
FWhat does friction make, when moving parts rub together? Write one word.
8
PSDoes oil increase or decrease friction between moving parts? Write the word.
9
PSIs friction helpful when a bicycle brake presses on the wheel? Write yes or no.
10
PSWorking scientifically. Plan a fair test. Write one thing that must stay the same in a test of which surface makes more friction. Write one thing.
11
RExplain why friction makes your hands warm when you rub them. Write one sentence.
12
RExplain why a car needs friction between its tyres and the road to stop. Write one sentence.
9.5

Comparing gravity, resistance and friction

Year 5
F1 and F2: compare the forces that act on falling and moving objects, and decide which force is acting
Video lesson: Comparing gravity, resistance and frictionComing soon
Story. Priya drops a sheet of paper and a small stone from the same height. The stone hits the floor first. “Gravity pulls them both,” she says. “So why does the paper fall more slowly?” Mr Patel says: “Air resistance pushes up against the paper.”

Several forces can act on a falling or moving object at the same time:

ForceWhat it doesDirection it acts
gravitypulls objects towards the Earthdownwards, towards the centre of the Earth
air resistancepushes against moving things in airagainst the motion
water resistancepushes against moving things in wateragainst the motion
frictionacts between surfaces that rubagainst the motion

Gravity pulls every object towards the Earth. Air resistance, water resistance and friction all push against the motion. This is why a falling object can fall more slowly than gravity alone would make it fall.

Key ideas

  • Gravity pulls objects towards the Earth, downwards.
  • Air resistance, water resistance and friction act against the motion.
  • Gravity acts at a distance, but friction needs surfaces that touch and rub.
  • Several forces can act together on the same object.
Worked example 9.5.1
Which force pulls a falling object towards the Earth? Write the word.

Method. Read the table.

  1. Read the first row. The first row says gravity pulls objects towards the Earth.
    gravity
  2. Name the force. So the force is gravity.
    gravity
  3. Write the answer.
    gravity

Check. Gravity acts on every object. ✓

Worked example 9.5.2
Which force slows a paper sheet falling through air? Write the words.

Method. Think about the paper in air.

  1. Think about the air. The paper moves through air, and air pushes against it.
    pushes against it
  2. Name the force. The force is air resistance.
    air resistance
  3. Write the answer.
    air resistance

Check. The flat paper has more air resistance than a crumpled ball. ✓

Worked example 9.5.3
Which force slows a box sliding across the floor? Write the word.

Method. Think about the box and the floor.

  1. Think about the surfaces. The box and the floor rub together.
    rub together
  2. Name the force. The force that slows the box is friction.
    friction
  3. Write the answer.
    friction

Check. Friction acts between the box and the floor. ✓

Watch out

Watch out: gravity is always there, but air resistance, water resistance and friction only act when something is moving through air or water, or when surfaces rub.

Try it (with your teacher or a grown-up). With your teacher, drop a sheet of paper flat and then crumpled into a ball, from the same height, onto a rug. Then drop a small stone, the same height. Which falls first? Which force makes the difference? Write one sentence about your result.

Exam tip

Grown-up tip. Ask: “Which force pulls everything down? Which force pushes against the paper?” Keep the drop low, on a soft surface.

Exercise 9E  Comparing gravity, resistance and friction

1
FWhich force pulls objects towards the Earth? Write the word.
2
FWhich force pushes against a falling object, through air? Write the words.
3
FWhich force slows a boat moving through water? Write the words.
4
FWhich force acts between two surfaces that rub? Write the word.
5
PSWhich force acts at a distance, so it does not need the objects to touch? Write the word.
6
PSWhich force needs two surfaces that rub: gravity, or friction? Write the word.
7
PSDoes a force from air act against a falling paper sheet? Write yes or no.
8
PSPriya says: “Air resistance pulls the paper to the ground.” Is Priya right? Write yes or no.
9
PSWorking scientifically. Compare forces. Which of these forces acts on a falling paper sheet, and against its motion: gravity, or air resistance? Write the word.
10
RExplain why a falling paper sheet takes longer to reach the floor than a stone dropped from the same height. Write one sentence.
11
RExplain why both objects in section 9.5 are pulled by gravity, even though they fall at different speeds. Write one sentence.

Chapter summary

SkillMethod
GravityGravity pulls every object towards the Earth. An unsupported object falls because of gravity.
Air resistanceA force from air that pushes against moving things. A larger flat surface has more air resistance.
Water resistanceA force from water that pushes against moving things. Streamlined shapes have less water resistance.
FrictionA force between surfaces that rub. It acts against the motion, can make heat, and is reduced by oil.
Comparing forcesSeveral forces can act together. Gravity acts at a distance; friction needs surfaces that rub.

Can you…?

  • I can explain that gravity pulls unsupported objects towards the Earth
  • I can describe how air resistance slows a falling object, and why a larger surface has more
  • I can describe how water resistance slows an object, and how a streamlined shape helps
  • I can explain that friction acts between surfaces that rub, against the motion
  • I can read a bar chart of a fair test on fall times

Key terms

gravity
a force that pulls objects towards the Earth, acting at a distance
unsupported
not held up by anything, so the object is free to fall
air resistance
a force from air that pushes against moving things, and slows them down
water resistance
a force from water that pushes against moving things, and slows them down
friction
a force between surfaces that rub, which acts against the motion
streamlined
smooth and pointed, so that air or water can flow past with less resistance
fair test
a test in which only one thing is changed, and everything else is kept the same
mean
the total of several results, divided by how many results there are

Exercise 9Z  Check-up

1
What force pulls an unsupported object towards the Earth? Write the word.
2
Does a book on a table fall? Write yes or no.
3
Which force slows a moving object through air? Write the words.
4
Look at the table in section 9.2. What is the mean time for the 200 cm² parachute, in tenths of a second? Write the number.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
5
Which shape has less water resistance: a flat, blunt shape, or a smooth, pointed shape? Write the words.
6
What is the name of the force that acts between two surfaces that rub? Write the word.
7
Look at the table in section 9.4. Which example uses oil to reduce friction? Write the words.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip
8
Fill in the gap: friction acts ___ the motion of a moving object. Write one word.
9
Which force acts between a box and the floor, slowing the box as it slides? Write the word.
10
Explain why a crumpled paper ball falls faster than a flat sheet of the same paper. Write one sentence.

Total 17 marks. Allow about 17 minutes.

Exercise 9X  Practice test questions

1
FWhat force pulls objects towards the Earth? Write the word.[1 mark]
2
FWhich force acts between two surfaces that rub, and slows a moving object? Write the word.[1 mark]
3
FWrite the name of the force that slows down a moving object in water. Write the words.[1 mark]
4
FLook at the table in section 9.2. What is the mean time for the 400 cm² parachute, in tenths of a second? Write the number.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
[1 mark]
5
FLook at the table in section 9.2. Work out how many tenths of a second longer the 300 cm² parachute took than the 100 cm² parachute, on average. Write the number.
Parachute area (cm²)Trial 1 (tenths of a second)Trial 2Trial 3Mean (tenths of a second)
1008798
2001011910
30012111312
40016151716
[2 marks]
6
FLook at the table in section 9.4. Name one example from the table where friction helps us. Write the example.
ExampleWhat happens
rubbing your hands together makes them warmfriction makes heat
a bicycle brake pad pressing on the wheelfriction slows the wheel
oil put on a moving partless friction, so less wear
shoes gripping a wet floormore friction helps you not to slip
[2 marks]
7
FLook at the picture of the boat shapes in section 9.3. Which shape has more water resistance? Write the words.
blunt shape: more resistancestreamlined: less resistancewater resistance pushes back against the motion (orange)
[2 marks]
8
RExplain why a large parachute falls more slowly than a small one. Write one sentence.[2 marks]
9
RExplain why friction helps a car to stop. Write one sentence.[2 marks]
10
RExplain why a ball falls when it is dropped, and name the force that makes it fall. Write two sentences.[3 marks]
← Chapter 8: The Earth, Sun and MoonChapter 10: Levers, pulleys and gears →

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