8-30-07

Friction is a sticky force that slows things down or keeps them from sliding.
Friction is a measure of how much two surfaces resist sliding.

Different materials have more or less friction. The student should be able to list examples from experiments in the activity:

• Rubber has lots.
• Waxed paper has less.
• Oil and water can reduce friction.
• Rougher surfaces (e.g. sandpaper) have more than smoother surfaces (e.g. wood or metal).

Ways to measure friction:

• If there is less friction, something will start sliding down a slide at a lower angle.
• If there is less friction, something will get going faster down a slide.
• If there is less friction, something will coast farther when pushed.
• If there is less friction, it will take less force to pull something horizontally.

If there were no friction, things would keep going forever. They can't slow down and they can't change direction.

Friction happens because atoms on the two surfaces stick to each other. It takes energy to break them apart and make the object slide.

Friction changes the energy of motion into heat energy, and the surfaces get hotter.

• When there is more friction, the surfaces heat up more.
• When there is less friction, the surfaces heat up less.