Year 3 Science: Friction
Part of the Year 3 Science forces chapter. Chapter overview · whole chapter on one page
Friction
Friction is a force that acts between two surfaces that touch and rub against each other. Friction slows down moving things. It always acts against the direction of movement.
Rough surfaces make more friction than smooth surfaces. A block sliding on sandpaper slows down much faster than the same block sliding on a smooth tray.
Friction can help us, or it can get in the way. The table gives some examples.
| Example | Helps or gets in the way? |
|---|---|
| Shoes grip the floor, so you do not slip | helps |
| Brakes press on a bicycle wheel to slow it down | helps |
| A sledge slows down on the grass | gets in the way |
| Car tyres grip the road, so the car can stop | helps |
| A toy car slows down on thick carpet | gets in the way |
| Moving parts of a machine rub together and wear out | gets in the way |
Key ideas
- Friction is a force that slows down moving things.
- Friction acts between two surfaces that touch and rub.
- Friction acts against the direction of movement.
- Rough surfaces make more friction than smooth surfaces.
- Friction can help, for example by stopping us from slipping, or it can get in the way.
Method. Find the row about the sledge.
- Find the row. The row says a sledge slows down on the grass.sledge
- Read the answer. The answer in the second column is gets in the way.gets in the way
- Write the answer. gets in the way
Check. Friction slows the sledge, which is not what we want here. ✓
Method. Look for the example about slipping.
- Read the table. The row about shoes says they grip the floor, so you do not slip.grip the floor
- Write the example. So the example is shoes gripping the floor.Shoes grip the floor
- Write the answer. Shoes grip the floor, so you do not slip
Check. Friction helps your shoes grip the floor. ✓
Method. Read the key idea in section 9.5.
- Read the key idea. Friction acts between two surfaces that touch and rub.touch and rub
- Find the missing word. The gap comes after touching and, so the missing word is the word for rubbing.rub
- Write the answer. rubbing
Check. Touching and rubbing both describe the two surfaces. ✓
Watch out
Watch out: friction is not always bad. Without friction, your shoes would slip on the floor, so friction helps you walk.
Try it at home or school (with a grown-up). Choose one object, such as a plastic lid. With a grown-up, give it the same gentle push on a smooth floor, and then on a towel or a rug. Which surface makes it slide less far? Repeat each test three times, and find the average distance. Keep to a clear floor, with no one walking on it.
Exam tip
Grown-up tip. Ask: “Where does the friction come from? Which surface made the lid slide less far?” Let your child use the words friction, rough and smooth.
Exercise 9E Friction
Method. Read the key idea in section 9.5.
- Read the key idea. Friction is a force that acts between two surfaces that rub and slows down moving things.friction
- Write the answer. friction
Check. Friction is the force that slows things down. ✓
Method. Think about the direction of friction.
- Think about the direction. Friction acts against the direction of movement.against
- Decide. So friction makes a moving object slow down.slow down
- Write the answer. slow down
Check. Friction never makes a moving object go faster. ✓
Method. Read the key idea in section 9.5.
- Read the key idea. Friction acts against the direction of movement.movement
- Write the answer. movement
Check. Against the direction of movement means the opposite way. ✓
Method. Think about rough and smooth surfaces.
- Think about the rough one. Sandpaper is rough, so it makes more friction.rough
- Choose. So sandpaper makes more friction.Sandpaper
- Write the answer. Sandpaper
Check. A smooth tray makes less friction. ✓
Method. Find the row about the brakes.
- Find the row. The row says brakes press on a bicycle wheel to slow it down.brakes
- Read the answer. The answer in the second column is helps.helps
- Write the answer. helps
Check. Friction between the brake and the wheel slows the bicycle. ✓
Method. Count the helps rows.
- Read the second column. The rows that say helps are shoes, brakes and car tyres.three helps
- Count them. There are three examples where friction helps.3
- Write the answer. 3
Check. The other three examples say gets in the way. ✓
Method. Look at the rows that say gets in the way.
- Read the rows. Three rows say gets in the way: the sledge, the toy car on carpet, and the moving parts of a machine.three rows
- Write one. Any one of these is a correct example.one example
- Write the answer. Accept any one of: a sledge slows down on the grass; a toy car slows down on thick carpet; moving parts of a machine rub together and wear out.
Check. Each of these examples has friction slowing something down. ✓
Method. Think about what the friction does to the car.
- Think about the car. The carpet makes friction, which slows the car down.slows the car
- Decide. Slowing the car is not what we want here, so friction gets in the way.gets in the way
- Write the answer. gets in the way
Check. The carpet is rough, so it slows the car quickly. ✓
Method. Think about grit and friction.
- Think about the grit. Grit makes the road rougher, so it makes more friction and helps the tyres grip.more friction
- Decide. So Yusuf is not right; grit makes the road grippier.no
- Write the answer. no
Check. Grit on an icy road helps the tyres grip. ✓
Method. Think about what makes a test fair.
- Think about the test. Only the surface should change; the object, the push and the starting place must stay the same.stay the same
- Write one thing. For example, use the same sock each time.same sock
- Write the answer. Accept any one of: the same sock, the same push, the same starting place.
Check. Change only one thing in a fair test. ✓
Method. Think about the tyres and the road.
- Think about the tyres. The tyres grip the road, and the friction between them slows the car.grip the road
- Write the sentence. So friction helps the car to stop.helps the car to stop
- Write the answer. Accept any sentence that says friction between the tyres and the road slows the car and stops it.
Check. Friction helps the brakes to stop the car. ✓