ACARA v9 CONTENT DESCRIPTION “describe pushes and pulls in terms of strength and direction and predict the effect of these forces on objects’ motion and shape”
Builds on the everyday play of moving things about: rolling a ball, opening a door, pulling a wagon. Here we give those actions their two science words, push and pull, and notice they each have a strength and a direction.
A push and a pull
A force is just a push or a pull. When you push a thing it goes away from you. When you pull a thing it comes toward you. Every push and pull also has a strength, how hard it is, and a direction, which way it points.
A push or a pull
A push moves a thing away from you. A pull brings a thing toward you. Try both.
You pushed the ball, so it went away from your hand. A push always moves a thing away from you.
How strong is the push?
A soft push has only a little strength, so the ball moves a little way. A hard push has a lot of strength, so the ball goes far. The harder you push, the further the thing goes.
A strong push goes far
A harder push has more strength, so it sends the ball further. A soft push only moves it a little.
A soft push has little strength, so the ball only moves a short way.
Which way does it point?
A push points a way. The thing always moves the same way you push it. Point the push to the side and it goes to the side. Point it up and it goes up. So a push has a direction, not just a strength.
Which way you push
A push has a direction too. Point the push a different way and the ball goes a different way.
The ball always goes the same way you push it. Point the push right, and the ball moves right. The direction of the push picks the direction of the move.
Forces can change shape too
A push or a pull does not only move a thing. It can change its shape. Press a soft ball and it squashes flat. Pull the ends of soft dough and it stretches long. A strong enough force can bend, squash or stretch the things around us.
Forces can change shape
A push or a pull can change how a thing moves, and it can also change its shape.
When no force acts, the soft ball keeps its round shape. A push or a pull is what changes it.
Guess before you look
Once you know that a pull brings a thing toward the pull, you can predict what will happen before it happens. The rope on the wagon is pulled to the left, so you can say, before it even moves, that the wagon will roll left.
Predict, then see
The rope is pulled to the left. Guess which way the wagon rolls, then reveal to check.
Pick a way first. Think about which way the pull points.
Why this matters
Every time we move something, a push or a pull is doing it. Knowing that forces have a strength and a direction, and that they can change how a thing moves and its shape, lets us predict what will happen. This is the first step toward all the science of forces in later years.
Quick self-check
1. You push a toy car. Which way does it go?
2. A hard push and a soft push. Which one sends the ball further?
3. You want the ball to go up. Which way do you push it?
4. You press a soft ball hard between your hands. What happens to it?
5. A rope on a wagon is pulled to the left. Which way will the wagon roll?