Re: [Phys-L] ?conservation of _internal_ energy

[Carl Mungan <mungan@usna.edu>]

> > > Why certainly work is being done by the `blue' box on the `red' box and the `red' box on the `blue' box via the interactive forces (which must be equal and opposite in direction of course).
> > >
> > > Good Luck,
> > >
> > > Herb Schulz
> > > (herbs at wideopenwest dot com)
> >
> >
> > You really want to say that?
> >
> > How about this case: A guy on roller skates pushes off from a rigid wall. System = man. Any work done on the system? Does his internal energy change?
> >
> > Further, in the real world, the guy will get a bit hotter if he does this several times. Any heat transferred to or from him (on short timescales)?
>
> Howdy,
>
> Do I really want to say the two forces must be equal and opposite? Isn't that Newton's 3rd Law?

No, do you really want to say work is done on one box by the other?

> I did NOT say the work done by the forces was the same. 


So are they or aren’t they? The two boxes are symmetrically arranged! So they have to be the same. In fact, they’re both zero. But I’m open to hearing you prove otherwise. So far you keep talking about the forces. We all agree on the forces. It’s the displacements we want to hear you discuss.

In any case, try my problem and answer the three questions I asked: work = ? change in internal energy = ? heat transfer = ?

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Carl E Mungan, Assoc Prof of Physics  410-293-6680 (O) -3729 (F)
Naval Academy Stop 9b, 572C Holloway Rd, Annapolis MD 21402-1363 
mailto:mungan@usna.edu     http://usna.edu/Users/physics/mungan/