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Re: [Phys-l] teaching energy



On Oct 3, 2006, at 12:21 PM, John Clement wrote:

No, viewpoint number 2 is not valid. If gravitational potential energy can
not be in the ball because the presence of the Earth is necessary for there
to be GPE. Now it is certainly associated with objects (note the plural),
but then you have #3.

SNIP
I agree with eliminating #2, even for kinetic energy (below).

Now with kinetic energy, the energy is in the object. With thermal energy,
the energy is in various physical places such as the two objects that are
rubbing against each other...

SNIP
I disagree with your first sentence. KE is not in the object but also depends on other objects; velocity is measured relative to a system. A thrown baseball on a moving train has a different KE in the frame of the train than it does according to an external stationary observer. Even KE requires a system.

John M. Clement
Houston, TX

On 10/03/2006 09:48 AM, Robert Cohen wrote:
I've been skimming through the posts and I think there are three points
of view:

1. Energy is associated with fields.
2. Energy is associated with objects.
3. Energy is associated with systems of objects.

I agree.

All three viewpoints are valid, and can be considered a chain of
successive approximations, in the order (1), (3), (2).



Dan M

Dan MacIsaac, Associate Professor of Physics, SUNY-Buffalo State College
222SciBldg BSC, 1300 Elmwood Ave, Buffalo NY 14222 USA 716-878-3802
<macisadl@buffalostate.edu> <http://PhysicsEd.BuffaloState.edu>