Why Moving Things Keep Moving
- Physics
- Ages 8–11 · Grades 3–5
- Hands-on experiment
What you’ll find out
- A moving object keeps moving unless a force acts on it.
- Friction is a force that slows things down.
- Heavier objects are harder to start and stop.
No sign-up and no real names. In the lesson you check your understanding as you read, run the experiment yourself, and practise until it sticks.
Things keep going on their own
If you roll a ball across the floor, it keeps going after your hand has let go. You pushed it once, at the start. Nothing is pushing it now. A moving object keeps moving all by itself. It needs a force only to start moving, to stop, or to change direction.
Friction slows things down
The ball does stop eventually, though. That is because of a force called friction. Friction happens whenever two surfaces rub against each other. A ball rolled on carpet stops quickly because carpet has a lot of friction. A puck slid on ice travels much further, because ice has very little friction.
Mass makes it harder to change
Try pushing an empty shopping trolley — it starts moving easily. Now fill it with heavy shopping. It takes much more effort to get going, and much more effort to stop. The more mass an object has, the bigger the force you need to change its motion.
Curriculum links: NGSS 3-PS2-1 · NGSS MS-PS2-2