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A ball is dropped on a horizontal ground, bounces repeatedly, each time reaching a lower height, and eventually comes to rest. If this event is filmed and played in reverse, the reverse process (ball spontaneously bouncing higher and higher) cannot occur in nature. Which law of physics most directly explains why?

1. Kelvin-Planck's statement of second law of thermodynamics.
2. Clausius' statement of second law of thermodynamics.
3. Carnot's principle.
4. First law of thermodynamics.

Correct answer: Kelvin-Planck's statement of second law of thermodynamics.

Solution

In the forward process, KE of the ball is irreversibly converted to heat via inelastic collisions. The reverse would require heat from the ground to convert spontaneously and completely to ordered mechanical energy (KE of ball) — this is exactly what the Kelvin-Planck statement of the second law forbids: no process whose sole result is absorbing heat from a reservoir and converting it entirely to work (organized energy).

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