Pushes, pulls and motion

What makes things move?

A ball sits still on the grass. It won’t move by itself. To make it move, you have to kick it, throw it or roll it. You need a force. A force is a push or a pull.

Pushes and pulls

Some actions use both. When you ride a bike, you push the pedals down, and the chain pulls the wheel around.

Forces change motion

When something moves from one place to another, it is in motion. Forces can change motion in many ways.

A force can:

• start something moving (kicking a still ball)
• stop something moving (catching a ball)
• make something go faster (pushing a swing harder)
• make something go slower (pressing a bike brake)
• change its direction (hitting a ball with a bat)
• change its shape (squishing playdough)

Big and small forces

A bigger force makes a bigger change.

• Tap a ball gently, and it rolls a little way.
• Kick it hard, and it zooms across the field!

Heavy things need a bigger push or pull to move than light things. It’s easy to push an empty box but hard to push a box full of books.

Speed and direction

Speed tells how fast something moves. A cheetah has a high speed. A snail has a low speed.

Direction is the way something moves: up, down, forward, backward, left or right. When you throw a ball up, it goes up, then gravity pulls it back down.

Gravity: a pull you can’t see

Gravity is a pull. It pulls everything toward the ground. That’s why:

• a dropped apple falls down, not up
• you come back down when you jump
• water flows downhill

Gravity is a force you can’t see, but you can see what it does.

Friction: a force that slows things down

Friction happens when two surfaces rub together. It slows things down.

• A ball rolls far on a smooth floor but stops quickly on grass or carpet.
• Rubbing your hands together makes them warm because of friction.
• Sneakers have bumpy bottoms to give more friction, so you don’t slip.

Ice has very little friction. That’s why it’s slippery!

Magnets push and pull too

Magnets can push or pull some metal things without even touching them. A magnet pulls a paper clip toward it. Two magnets can push each other away.

In the real world

• Soccer players use different-sized kicks to pass or to shoot.
• Ramps help push heavy things up into trucks.
• Brakes on a bike use friction to stop.

Common mistakes

• Thinking things stop because they "run out" of push. Friction and other forces slow them down.
• Thinking only living things can push or pull. Wind pushes sailboats; magnets pull nails.

Try it yourself

1. Roll a toy car on a smooth floor, then on a carpet. Where does it go farther? Why?
2. Push a toy car gently, then harder. What changes?
3. Make a list of five pushes and five pulls you do every day.

Quick recap

• A force is a push or a pull.
• Forces can start, stop, speed up, slow down or change the direction of motion.
• Bigger forces make bigger changes.
• Gravity pulls things down.
• Friction slows things down.