# Heat generated by friction

## Main Question or Discussion Point

How does one calculate the heat generated by a force of friction with respect to time?

Let's stick with constant mass and assume that we know everything but heat.

Thanks for looking in,

MJ

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All of the energy dissipated by friction can generally being dissipated thermally --> i.e. through heat.
Calculate the work done by friction, and there it is.

How does one calculate the heat generated by a force of friction with respect to time?Let's stick with constant mass and assume that we know everything but heat.
A very simple model: a mass m, moving at constant velocity v, on a level surface, with an applied constant force F and kinetic friction f acting in the opposite direction:

In this case the power of the applied force is F.v (which here is just F*v) and, by conservation of energy, the only energy transfer is to the internal energy of the block/floor. Hence the 'heat generated' with repect to time is just F*v - in Watts.

I think this is correct. Hope this helps. Or is it too simple a model?

All of the energy dissipated by friction can generally being dissipated thermally --> i.e. through heat.
Calculate the work done by friction, and there it is.
If you're pulling an object but the friction of the floor is stronger than you (hence, no movement -> no work), does the object/floor still warm up a little bit?

If it doesn't, where is the energy (which you're consuming in the futile effort of pulling the object) dissipated?

If you're pulling an object but the friction of the floor is stronger than you (hence, no movement -> no work), does the object/floor still warm up a little bit?

If it doesn't, where is the energy (which you're consuming in the futile effort of pulling the object) dissipated?

russ_watters
Mentor
If you're pulling an object but the friction of the floor is stronger than you (hence, no movement -> no work), does the object/floor still warm up a little bit?

If it doesn't, where is the energy (which you're consuming in the futile effort of pulling the object) dissipated?
Biochemical energy is expended just clenching muscles. A compressed spring, on the other hand, doesn't expend energy to exert a static force. So you could say that your energy efficiency is zero when applying a static force.

Biochemical energy is expended just clenching muscles. A compressed spring, on the other hand, doesn't expend energy to exert a static force. So you could say that your energy efficiency is zero when applying a static force.
So there is no minimal heating of the object/floor in that case?

So there is no minimal heating of the object/floor in that case?
Theoretically: No. Practically: Yes. When a force is exerted onto smt anh presses it, it may deforms and that gives off heat.

russ_watters
Mentor
Ehh, sort of. It may generate heat while it is being compressed, but once compressed and left in a static state, it will generate no more heat.

Ehh, sort of. It may generate heat while it is being compressed, but once compressed and left in a static state, it will generate no more heat.
Clear, thanks!

It makes sense, otherwise I suppose that any object under some sort of tension/compression (even that of its own weight) would give off heat and therefore slowly lose energy...

"It makes sense, otherwise I suppose that any object under some sort of tension/compression (even that of its own weight) would give off heat and therefore slowly lose energy..."

errr.... no, unless the volume is changing in which case yes. But basically the answer to the OP's question is that the kinetic energy lost due to friction is basically the heat energy