REPOSTING WHAT I ASSUME WAS LOST during the weekend
If somebody asked me today what is wrong with 'energy=ability to do work'
and why people objected (very categorically) to the term 'thermal energy'
I would say that the first implies 'work is mechanical energy' while the
second can possibly be confused with heat. Do not say am I not learning.
Macroscopic work is not energy, it is a process by which mechanical energy
(kinetic, elastic or gravitational) can be either gained or lost by a
system. It is also the name of a quantity (force times distance) which is
used to know (to measure) how much mechanical energy was lost or gained.
Likewise, heat is not energy. The word heating refers to a macroscopic
process through which thermal energy is either added or removed from a
system. It is also the name of a quantity (c*m*dT) which is used to know
(to measure) how much thermal energy was lost or gained.
I heard somewhere a statement that "how much heat in a body?" is like
asking how much rain is in the ocean." Some water entered in the form of
drops of rain, some in the form of flowing streams and rivers. There is
no way of knowing which part is which. And somebody makes an observation
that these two ways (of changing the amount of water in the ocean) are
not the whole story. A "third processes" must be recognized; water may
enter, for example, through pipes connected to man-made synthesizing
plants. Evaporation is called "negative rain".
Why am I using the word 'thermal energy' instead of what some people
prefer to call 'internal energy'? There are two ways of looking at this.
First, 'internal' means being inside of something. In that sense thermal
energy is internal. But the kinetic energy of a sliding cube is also
internal (in our cube-plate system). Or think about the flywheel of an
engine, etc. We do distinguish the macroscopic and miscroscopic internal
energies and specific words are needed to make a distinction. Find a
better word and I will stop using 'thermal'. Actually am not the only one
to use this word. Why were there so much fuss about it.
Unless there are no objections, I suggest that the above is accepted as
a summary of what we learned in this thread about terminology. Then we
should move to a much more serious subject, the teaching. Is teaching
energy before work and heat is possible in an elementary course? Is it
desirable?
Ludwik Kowalski
P.S.
The above was composed before the use of Martian words was suggested.