Re: [Phys-l] work/KE (was: Equations again)

["Bob LaMontagne" <rlamont@postoffice.providence.edu>]

Not to step into a hornet's nest, but isn't the work done by the
non-conservative forces equal to the change in the total mechanical energy
of a system? Sort of a W(non-con) = delta E ? I find this very useful when
dealing with friction, flow work in fluids (Bournouli), etc.

Bob at PC

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu
[mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of John Denker
Sent: Monday, May 01, 2006 5:46 PM
To: Forum for Physics Educators
Subject: [Phys-l] work/KE (was: Equations again)

JMGreen wrote:
> I realize that the following questions are not nearly as 
> sophisticated as the current thread, but a reply or two would be very 
> helpful.   In the work/energy theorem, W=delta E, should W be thought 
> of as energy per se?

That's a quagmire.

1) First of all, the English is ambiguous.  "The" work could be considered
_part_ of "the" energy ... but cannot by itself be considered "the" energy.

2) At a deeper level, there is AFAIK not any work/energy theorem that says
"W=delta E".  The question probably refers to "the" work/KE theorem.

3) Even with that correction, we have problems, because there are various
definitions of KE (depending on lengthscale) and an even greater variety
of definitions of work.

Some discussion of points (2) and (3) can be found at
   http://www.av8n.com/physics/kinetic-energy.htm
and references therein.

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