3
Slowing down and stopping
Workbook 2: Topic 2.3, p. 25
GoalExplain that a force can slow down or stop a moving object, and test how the size of a push changes how far a ball rolls.
New words
slow down · to start going more slowlybrake · the part that makes a bicycle or car slow down and stopstop · to stay in one place and not move
Explanation
Forces can also slow things down and stop them. When Kenji pulls the brake on his bicycle, the bicycle slows down and stops. A goalkeeper uses a force to stop a fast ball. If you drag your foot on the ground on a scooter, you slow down. A push or pull the other way makes a moving thing slower. We can test this. We give a ball a small push and then a big push, and we watch how far it goes. We keep the ball and the floor the same.
Worked examples
Kenji pulls the brake. The bicycle slows down and stops.
A puppy runs after a ball. Its owner pulls back gently on the lead, so the puppy slows down.
| Push | Steps the ball rolled |
|---|---|
| small | 2 |
| big | 6 |
Class activity
Rolling test (with an adult): use one ball on a smooth floor. First predict: will a big push make it roll further? Give it a small push and count the steps it rolls. Then a big push. Do each three times, and write your results in a table. Keep the same ball and floor each time.
Practice
1
What makes a bicycle slow down and stop?
Pulling the brakes.
2
In Ana’s ball test, a small push rolled the ball 3 steps and a big push rolled it 8 steps. Which push made it go further?
| Push | Steps |
|---|---|
| small | 3 |
| big | 8 |
The big push (8 steps).
3
Name two things we keep the same to make the rolling test fair.
The same ball and the same floor (also the same person pushing).
4
Does dragging your foot on a scooter make you slow down or speed up?
Slow down.