Practice Set 1 — Nature of Friction
Cause of friction, factors, and types of friction.
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Practice Set 2 — Controlling Friction and Drag
Increasing and reducing friction; fluid friction and streamlining.
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Quick Q&A Before You Revise
Would there be friction between two surfaces if there were no irregularities?
Friction mainly arises from the interlocking of surface irregularities and from attraction between surface molecules. If surfaces were perfectly smooth and very close, the molecular attraction could actually make them stick strongly, so some resistance would remain.
Why does a ball rolling on the ground slow down and stop?
Rolling friction between the ball and the ground (and a little air drag) continuously opposes its motion and gradually reduces its speed to zero.
Does friction produce heat?
Yes. Rubbing surfaces together converts kinetic energy into heat — which is why we rub our palms to warm them and why machine parts get hot.