Lesson 7 of 15
The surface pushes back
Show on a big screenA rolling ball slows down and stops. Something pushes back on it.
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Step 1 of 3
- A crate slides right.
- The floor pushes back. Friction points left, against the sliding.
- The crate slows down.
The rule
Friction is the force between two surfaces that rub. It acts against the motion, or against the push to move. It is a contact force.
Tiny bumps on both surfaces lock together, so sliding is harder. Rougher surfaces give more friction.
Air and water cause friction too. Planes and boats have shapes that reduce it.
Watch out!
A smooth surface still has friction. A ball on glass stops too. The ball goes further before it stops.
Try the lab to finish this lesson.