Re: positive and negative work

[Scott Goelzer <sgoelzer@EARTHLINK.NET>]

>
snip
> These screw jacks can exert a force. The force may reduce gravitational
> acceleration - which is the physics conception of negative work,
> or the force may increase the acceleration provided by gravity - which is the
> physics conception of  positive work.
> The physiological mechanism - the heat engine driven screw jack doing work
> - works the same either way.

snip

> Brian Whatcott


This is the best analogy I have heard yet - thanks.

Another opinion to be scorned:

Spending class time getting students to learn an arbitrary sign convention
is pointless. An object is either increasing in energy (having work done on
it) and displaying a symptom (faster, higher, hotter, more stretched or
compressed, diff. chemicals ...) or decreasing energy (doing work) and
displaying the reverse symptoms. Why is important to _decide_ what sign each
function is as long as one is consistent? Is it important to the students
understanding of the world to know what many (actually quite few) consider
to be an accepted sign convention?

I have the same issues with gravity being _taught_ as neg. 9.8 m/s/s simply
because the bottom of the page in a math book is usually negative. Up is the
opposite sign of down - just be consistent.

Scott

*****************************
S.Goelzer
Physics Teacher
Coe - Brown Northwood Academy
Northwood NH 03261
603-942-5531 ext43
sgoelzer@coebrownacademy.com
*****************************