Re: Energy, etc

[John Denker <jsd@MONMOUTH.COM>]

At 10:47 PM 8/3/99 -0500, brian whatcott wrote:
>       Folks remind themselves that v is usually relative (?),

OK.  I will ignore the "usually" and the "(?)" which I assume are
tongue-in-cheek.

> so that kinetic energy is relative,

OK.  That's an unusual way to say it, but OK.

> and by changing their frame, they shift energy

Yes, of course.

> between the moving article to the scenery which
> was thought to be immobile. This means they believe they know how to
> 'relocalize' it!

Whoa!  You utterly lost me there.  Articles?  Scenery?  I don't know what
that is, but it's not physics.

===================

The concept of energy is useful because of the way it is used.  It is used
e.g. in conservation laws such as
        Energy(time 1) = Energy(time 2)

A change of reference frames in no way detracts from the validity of this
equation;  the change affects both sides equally.  The invariance of the
basic laws of motion has been known for 400 years;  the quantitative
invariance of energy in particular has been known for "only" 150 years or so.

At the other extreme, if you write equations of the form
          Energy in Moe's frame(time 1) = 19
          Energy in Joe's frame(time 2) = 37
you are free to do so, but don't be surprised if these manifestly
frame-dependent statements are frame-dependent.