Re: Running outside or treadmill

In article <slrnf2v1ml.14i.abuse@xxxxxxxxxxxxxxxx>,
Elflord <abuse@xxxxxxx> wrote:
On 2007-04-25, Robert Grumbine <bobg@xxxxxxxxx> wrote:
Not by the earth. Either you supply the energy, or you slow down.

I don't believe this is correct. If you are moving at X miles and hour,
and your foot hits the ground (at Xmph relative to the ground), it will
pretty quickly accelerate to ground speed, *and* you don't need to supply
energy for this to happen.

My knees say otherwise, as does my experience running on sheer ice
near the freezing point.

F = ma
W = Fd

I'm reluctant to accept the second equation, because it is only true for
very specific assumptions about the force and distance involved (work done
against a conservative force), I'm not convinced this is a proper application.
But, I can and will still argue that the treadmill and earth are the same.

If you're going to ignore the math (feel free to bring in math
or physics you think are more appropriate) then we're done.

But W = Fd works regardless of whether you're working with conservative
forces or not. Shove a box across a real (but level) floor, you
will do work that this recognizes. F = the frictional force,
d = distance you shove the box. It's incomplete, in that there are
other kinds of work possible. But you're arguing that there
is indeed an F and a d, you just don't work it out.

Show me where the nonzero d occurs while your foot is in contact
with the ground, at the same time as the ground provides a force in
the horizontal, and then I'll believe that W is not zero. I've
shown d not equal to zero for treadmill case, and shown how it is
that F can (but may not be) also be nonzero on the treadmill.

I think you're allowing yourself to be bamboozled by the differing frame
of reference. In both cases, you're using the earths frame of reference.

In the *runners* reference frame, d is non-zero in the earth picture.

Since you're not going to do the math, you're not going to
un-bamboozle anything.

--
Robert Grumbine http://www.radix.net/~bobg/ Science faqs and amateur activities notes and links.
Sagredo (Galileo Galilei) "You present these recondite matters with too much
evidence and ease; this great facility makes them less appreciated than they
would be had they been presented in a more abstruse manner." Two New Sciences
.

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