Rocket rolls a marble across a smooth floor. It zooms far away.
Then he rolls it across the fluffy rug. It stops quickly. "The rug is grabbing it!"
Raven rubs the rug with her fingers. "What do you notice about how it feels?"
Nova hovers low. "Even smooth things have tiny bumps," she says. "What happens when bumps meet?"
Every surface has tiny bumps, even ones that look smooth.
When two surfaces touch, their tiny bumps lock into each other.
To slide, the bumps must be pushed past each other. That is friction.
Rough surfaces have more bumps, so they make more friction.
A ball rolls more slowly on grass than on a smooth sidewalk.
Friction also grows when two surfaces press together harder.
An empty mat is easy to drag.
A mat with a person sitting on it is much harder to drag.
| Surface pair | More or less friction? |
|---|---|
| marble on a smooth floor | less |
| marble on a fluffy rug | more |
| ball on a sidewalk | less |
| ball on grass | more |
Super surface science! Tomorrow we see how tires use friction to grip the ground.