Re: Energy, etc

[DEVARAKONDA VENKATA NARAYANA SARMA <narayana@HD1.DOT.NET.IN>]

So the work-energy theorem is dW = -dK is invalid!
Is there not a reaction of the wall on the person?
An infinitaly massive body acts like a force reflector.
When did all of this become the "out thing"?

regards,

sarma.
At 09:46 AM 8/5/99 +1000, Brian McInnes writes:
> Let me pick up a point on the periphery of the energy-localisation
> discussion.
>
> Robert A Cohen wrote (inter alia)
> >   As such, I prefer to say that an object's kinetic energy increases
> > because some force does work on the object
>
> I think we should be careful here in the use of the word object.
>
> The statement is necessarily true for a particle but it is not
> necessarily true for an extended object. Extended objects are real,
> particles are not.
>
> Suppose the object was a person wearing a pair of roller skates,
> standing on a polished floor and pushing against the wall of a room.
> The object's kinetic energy increases there is no work on the object
> by any force.  An object's kinetic energy can increase without work
> being done on it!
>
> A proper understanding and treatment of the first law of
> thermodynamics deals satisfactorily with this and all situations
> involving energy changes.  (Note I do not write energy transfers, much
> less energy flows.)
>
> Brian McInnes