Re: ENERGY WITH Q

[Ludwik Kowalski <kowalskiL@MAIL.MONTCLAIR.EDU>]

Robert Cohen wrote:

> How about if we rewrite the expression as

>       deltaE +/- Q = W?
>
> Here deltaE is energy, Q is energy and W is work.  Does
> this solve the ikely "misconceptions" that might arise when
> energy and work are on the same side of the expression?

Good question. Was the misconception (that both Q and W are
forms of energy) actually recognized by our PER friends? How
common is it? It would be interesting to collect data answering
Robert's question.

Here is an observation. What does KE=0.5*m*v^2 mean? It
it a definition of KE. It gives me a formula to calculate KE when
m and v are given. Energy on the left side and a mathematical
expression on the right side. Not very different from what
Denise's mother did to figure out how many blocks are in a
box she was not allowed to open. This definition of KE is
not arbitrary; mother nature "suggested it to us" through the
work-energy theorem.

Likewise, PEgrv=m*g*h is a definition; energy on the left side
and a mathematical expression on the right side. What was the
motivation for this definition? A desire to impose a philosophical
idea that something is conserved in the idealized world without
friction-like forces. The fact that the expression on the right side
is the same as for the work done against gravity does mean that
work is a form of energy. Work does not appear in the energy
conservation law (which in this case is KE+PEgrv=const).

That is why I prefer to introduce the First Law WITHOUT
addressing the issue of how the energy "traversing the system
boundary" (flowing, transmitted, going, drifting, shifting, or
penetrating, if you prefer) can be subdivided into two, three
or more components. This topic should be debated in a more
advanced course. IS THIS ACCEPTABLE?

By the way, I plan to have a web page summary of what,
according to MOST Phys-L-ers, is NOT WRONG in the
proposed sequence of energy topics. The URL will be posted
when the draft is ready, perhaps next weekend. I would very
much like to add a list of URLs for documents in which energy-
related topics are described by Phys-L-ers. So far I have only
three references: JohnD, JimG and JohnM. Who else would
like to share a web page document devoted to energy related
issues? Yes, any topics in physics is "energy related." But
you know what I want. The document should be about kinds
of energy and about the two laws of thermodynamics (for
student or new teachers of introductory physics courses).
Ludwik Kowalski