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In the expression for the largest static friction, what does the normal force represent?
AThe push applied along the surface
BThe weight of the surface below
CThe force perpendicular to the surface
DThe force needed to break contact
Answer & Solution
Correct answer: C. The force perpendicular to the surface
1. The limit on static friction is the coefficient of static friction times the normal force.
2. The normal force is the contact force acting perpendicular to the surface.
3. Pressing the surfaces together harder raises the normal force and so raises the friction limit.
4. The applied push acts along the surface and is a different force entirely.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section Magnitude of Static Friction_
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