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Q & A: thermodynamics of squash

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Most recent answer: 10/22/2007
Q:
The surface of a squash ball will warm up to an equilibrium temperature of 45C during a hard match. This temperature is maintained provided the rallies remain long and hard. My question is what is the temperature inside the squash ball? Here’s what I know. Outside temp = 45C Inside temp = ? Outside diamter = 40mm Inside diameter = 38mm Coefficient of thermal conductivty for rubber = 0.2 Watts/ degree-kelvin Any help or pointers would be greatly appreciated.
- Faraz Hussain (age 25)
Illinois Squash Club, Peoria, IL
A:
Faraz- Nice question.

Imagine you were an air molecule inside the ball. The only things you would bump into, other than air molecules like yourself, would be the walls of the ball, at 45 deg C. So you and your fellow molecules would also equilibrate at 45 deg C. Sometimes that's called the "zeroth law of thermodynamics"- that any two objects in equilibrium reach the same temperature. If you get a chance to take a course on thermodynamics, you will probably see how it can be derived from the Second Law of Thermodynamics, the basic principle that entropy always increases.

Mike W.

(published on 10/22/2007)

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