Re: ENERGY WITH Q

[Jim Green <JMGreen@SISNA.COM>]

> "Carl E. Mungan" wrote:
> > I posed this question the other day and I have not seen
> > an answer yet. Here it is again. I stop a block with a
> > string. No change in the block's thermal energy occurs.
> > Now I stop the block via sliding friction. The block's
> > thermal energy changes. Why does friction change the
> > thermal energy of an object but tension does not (in
> > these particular situations)?

Carl,   the only way to change the level of the property of energy of a
system  is to do work on the system.  If the work is done in such a manner
as to change the macroscopic motion of the system (eg the motion of the
CM),  the level of the internal/thermal energy does not change.  If the
work is done in such a manner as to change the microscopic motion of the
system statistically, then the internal/thermal energy of the system is
changed.   The work done by friction is done by smashing a chunk of stuff
into another in such a manner that the atoms are jostled but that the bulk
material is not jostled -- at least not in a major manner.   If you are
talking about a very large collection of marbles,  you have a big
analytical mess on your hands, unless you assume that all the marbles come
to rest and have bashed each other in such a manner as to jostle the
various atoms of the material and have not bashed the container.

All of thermodynamics is based fundamentally on the idea of statistics and
reasonable randomness -- and the steam engine.   Extensions are usually
called "thermal physics" -- for lack of a better appellation.


BTW -- I hold no meaning for  Eth or "convert KE"; and I am a bit confused
by the use of "H".

But then  I am old and senile.

Jim Green
mailto:JMGreen@sisna.com
http://users.sisna.com/jmgreen