alleryStart learning →In which direction does the force of friction act?
AAt right angles to the surface
BParallel to the contact surface
CVertically downward at all times
DAlong the line joining the centres
Answer & Solution
Correct answer: B. Parallel to the contact surface
1. Friction acts in the plane where the two surfaces touch.
2. That makes it parallel to the contact surface, not perpendicular to it.
3. Within that plane it points so as to oppose the motion, or the attempted motion.
4. The force perpendicular to the surface is the normal force, a separate force altogether.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section Friction_
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