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Re: [Phys-l] EM, is it energy



Attributing energy to the field rather than to an object influenced by the field is something worthwhile which I can pass on to my students. So if there is nothing under the influence of a field, regardless of field strength, there is no energy stored in the field. Thanks JB, this is something I must have missed in text books, or at least it wasn't put that way. This a helpful list.

----- Original Message ----- From: "John Barrer" <forcejb@yahoo.com>
To: "Forum for Physics Educators" <phys-l@carnot.physics.buffalo.edu>
Sent: Sunday, December 02, 2007 1:12 AM
Subject: Re: [Phys-l] EM, is it energy



--- Craig & Margaret Lucanus <lucanus@iinet.net.au>
wrote: SNIP

or when a book on a
shelf falls and loses PE,

This seems to imply that the book "has" PE. Not so. In
the book/Earth system (one always needs to define the
system when analyzing energy changes), the work done
by raising the book to the shelf results in an
increase of energy stored in the Earth's gravitational
field.

It may also be helpful to remember that since
computation of system energy is always reference
frame-dependent, the only thing that really matters is
CHANGE in the energy of a system.

John Barrere
Fresno Unified School District
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