Look at this ball resting on the floor. It is not moving. What could we do to make it start? What could we do to make it stop again?

Hands up: share your ideas.

Watch the moving picture.

What made the ball start? What made it stop? What made the box move?

Three force missions. Your group works at its own desks, and everyone has a go. After each go, one of you says what happened.

Word bank: push, pull · start, stop, turn, speed up, slow down

Mission 1: Stop on the spot. Put your counter on the start line, right below the box. Give it one push with one finger. Can you make it stop inside the box? What happens if your push is too gentle? What happens if it is too strong? Everyone has three tries.

Mission 2: Bounce round the corner. Start from the far side of the line, away from the box. Lay the book flat on the desk, on a slant, right ahead of your counter. Slide your counter at the side of the book. What does the counter do when it hits the book? Turn the book, bit by bit, until your counter bounces into the box.

Mission 3: Tow the pile. Put one book inside the string loop. Hook the pencil through the elastic band and pull slowly along the desk. Watch the band. How long is it just before the book starts to move? Write the length on your Investigation Journal page. What do you think will happen to the band with two books? Try it, then try three.

Before we write, let's say the three missions together.

Then finish the page: what a stronger push did, a drawing of your bounce, and what a bigger pile needs.

Word bank on the board: push, pull · start, stop, turn, speed up, slow down