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Friction is proportional to the normal force, but not to which quantity?
AThe area of surface in contact
BThe mass resting on the surface
CThe roughness of the surfaces
DThe material the surfaces are
Answer & Solution
Correct answer: A. The area of surface in contact
1. Doubling the normal force doubles the friction, so the two are proportional.
2. Spreading the same load over a larger area does not change the friction at all.
3. This feels wrong at first, which is why the result is called counterintuitive.
4. The materials involved do matter, but they enter through the coefficient, not the area.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section Making Connections: Submicroscopic Explanations of Friction_
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