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Re: Energy, etc



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