Re: The Rise and Fall of Simple Machines

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

I agree that simple machines are worth teaching and analyzing.

Leigh wrote:

> .... I would not miss the
> opportunity to introduce my students to a differential hoist in
> the laboratory session. They may have to go down to the auto shop
> to play with one, but no physicist should ever feel his education
> is complete if he hasn't done so. ....

In the past farming experience would often provide exposure to
simple machines. I wander in what fraction of US high schools
differential hoists are available and how many of those would
allow students to experiment with them? Perhaps simple machines
(and challenging student activities) should be made available as
standard science laboratory devices.

I do use a two pulley system, and the inclined plane, each year
to demonstrate that the work done at the input is nearly equal to
the work done at the output of a device. Can this be called the
"conservation of work" principle? I suspect that the "conservation
of energy" evolved from the "more primitive conservation of
work" idea. Is there any historical evidence to support this?

In the spirit of a Carnot diagram (a circle with arrows) a
simple machine has only two arrows: work in and work out.
The number of joules going in is slightly smaller than the
number of joules coming out. No joules would be lost in
an ideal machine (negligible mass and friction). This is
not very different from what we have in calorimetry,
except that here joules represent "heat" and the amount of
work done is negligible. Thus "conservation of heat" and
"conservation of work" before the conservation of energy.

Ludwik Kowalski