Science · Forces & motion
Gravity & friction
The forces that slow things down.
What slows things down?
When you roll a ball, it doesn't keep going forever. It slows down and stops. Two invisible forces make this happen: friction and gravity. Friction happens when surfaces rub together. Gravity is the pull that keeps us on the ground. Both forces work to slow moving things down.
Friction: The rubbing force
Friction is a force that happens when two things touch and rub. Try sliding a book across a rough carpet, then across a smooth table. The carpet has more friction, so the book stops faster. Smooth surfaces have less friction. Rough surfaces have more friction. Friction always works against the direction something is moving.
Gravity: The pulling force
Gravity pulls everything down towards the ground. When you drop a ball, gravity pulls it down. When you throw a ball up, gravity slows it down until it stops. Then gravity pulls it back down. Gravity always pulls towards the centre of the Earth.
How friction and gravity work together
Often both forces work at the same time. When you slide down a slide, gravity pulls you down. Friction between you and the slide slows you down a bit. Without friction, you would go very fast! Without gravity, you wouldn't slide down at all.
Testing these forces
You can see these forces in action everywhere. A rolling toy car stops because of friction with the floor. A parachute falls slowly because air friction slows it down. A bouncing ball doesn't bounce forever because gravity pulls it down and friction takes away energy. Scientists measure forces in units called newtons.
Worked examples
1. A toy car rolls down a ramp and stops on the carpet. Which forces slowed it down?
- First, think about what happened. The car rolled then stopped.
- Gravity pulled the car down the ramp to make it move.
- Friction between the wheels and carpet rubbed together.
- This friction force slowed the car until it stopped.
- Answer: Friction was the main force that slowed it down.
2. You throw a tennis ball straight up in the air. What slows it down?
- The ball goes up fast at first, then slower, then stops.
- Gravity pulls down on the ball the whole time.
- This pull works against the upward movement.
- Air friction also slows it a tiny bit.
- Answer: Gravity is the main force slowing the ball as it goes up.
3. Why does a sledge go faster on ice than on grass?
- Both surfaces have friction, but different amounts.
- Ice is very smooth, so it has low friction.
- Grass is rough, so it has high friction.
- Low friction means less slowing down.
- Answer: Ice has less friction, so the sledge slows down less.
Try it yourself
A book slides across a wooden table and stops. Name the force that slowed it down and explain why it happened.
Ready to test yourself?
Take a short topic test — every question maps to a syllabus point so you’ll see exactly which parts you’ve mastered.