Chronology Current Month Current Thread Current Date
[Year List] [Month List (current year)] [Date Index] [Thread Index] [Thread Prev] [Thread Next] [Date Prev] [Date Next]

Re: [Phys-l] energy is well defined



Jeff,
On Mon, 18 Feb 2008, Jeff Weitz wrote:

Hi everyone,
Why define "energy"? Look at the linguistic knots we get stuck in.

I agree. What's this obsession with definitions? Has anyone given an all inclusive definition of "force?"

I do like Feynmann's "currency of the universe." He was always elegant with language. Before I read that I was going to try for "the fundamental substance of the physical universe...at least for now."

Ludwik said: "One can say that energy is a concept similar to work." This bothers me a little bit. Energy is a fundamental, work is a process. They are similar like dirt (energy) and a shovel (work). Rather than the defining energy in terms of "work," I think a better, more developed concept is that work is a process (the process?) that moves (transfers) energy from place to place and object to object. Define work in terms of what it does to localized energy "content" (the work-energy theorem). Then say that work is done on an object by a force when the object has a component of motion (displacement) parallel to the force.

Jack Uretsky <jlu@hep.anl.gov> 2/18/2008 11:10 pm >>>

Hi Jeff-
How do you describe what happens when I mix a kilogram of 79
degree water with a kilogram of 40 degree water in an insulated container?
Regards,
Jack

Jack: The kinetic energy of the molecules in the 79 deg. water is redistributed to more molecules which had less KE on the average. The molecules do work on each other during collisions, gaining or losing KE with the ultimate result being a temperature between 79 and 40 (59.5 if we ignore the work done to the inside surface of the container) with an average KE per molecule corresponding to that temp. Were you looking for more than that?

Bill Nettles
Union University--yes, tornados did a lot of work here, massive increase in entropy, too.