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At the atomic scale, why do two surfaces get measurably warmer after being rubbed together?
AThe normal force alone converts directly into thermal energy
BAir trapped between the two surfaces compresses and warms up
CSurface atoms adhere and cause atomic lattices to vibrate into heat
DStatic electric charge builds up and discharges as heat
Answer & Solution
Correct answer: C. Surface atoms adhere and cause atomic lattices to vibrate into heat
1. When surfaces rub, surface atoms adhere to each other and cause atomic lattices to vibrate.
2. Those vibrations act like sound waves traveling through the material, and this vibrational energy converts into heat as it diminishes.
3. No trapped-air mechanism appears anywhere in this discussion, so that option is not supported.
4. The normal force is a mechanical push, not itself a form of thermal energy, so it cannot convert directly into heat.
5. Static charge buildup is not mentioned anywhere in the discussion of atomic-scale friction, so it is a distractor with no textual support.
_Source: OpenStax College Physics (CC BY 4.0), Ch 5 "Further Applications of Newton's Laws: Friction, Drag, and Elasticity", section 5.1 Friction_
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