Reusing dissipated energy

1. Jan 13, 2008

hammertime

This is a hypothetical question. Suppose you were to run a piece of sandpaper over a piece of wood repeatedly and quickly, thus heating the surface of the wood. The wood would then transfer that heat to the local molecules in the air, right? Could that energy which is transferred to the molecules somehow be harnessed? Couldn't this be a way to overcome the second law of thermodynamics?

2. Jan 13, 2008

HallsofIvy

Staff Emeritus
Yes, it would. And since you can't "overcome the second law of thermodynamics"....

References to using heat to do work depend upon there being a two different sources of heat, one being hotter than the other. Since that is, in a sense, a "structure", the situation is not completely random, you can do work by transferring heat from the hotter to the cooler. Of course, that then destroys the "structure", eventually reducing both sources to the same temperature.

3. Jan 13, 2008

Staff: Mentor

All the 2nd law tells you is that there is always going to be wasted heat. Even if you recover it, the next process you use it in is still going to waste some.