4.12. Friction http://www.ck12.org
FIGURE 4.23
Summary
- Friction is a force that opposes motion between any surfaces that are touching.
- Friction occurs because no surface is perfectly smooth.
- Rougher surfaces have more friction between them. Heavier objects also have more friction because they
press together with greater force. - Friction produces heat because it causes the molecules on rubbing surfaces to move faster and have more
energy.
Vocabulary
- friction: Force that opposes motion between two surfaces that are touching.
Explore More
Experiment with the effects of friction on the motion of a toy car in the activity at the following URL. Then take the
quiz to see how well you understand friction.
http://www.bbc.co.uk/schools/scienceclips/ages/8_9/friction.shtml
Review
- Define friction, and explain why it occurs.
- Identify two factors that affect friction.
- Why does friction warm your hands when you rub them together?
- Outside wooden steps may get slippery when they are wet. How could you make them less slippery?