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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)
Follow-up on this answer.
