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Re: [Phys-l] Food Liar's calorie chart

When you are jogging at constant speed, I suspect that a large fraction of the work you do is pushing your center of mass upward, giving it the energy to reach a peak height, an energy that is then lost in the inelastic collision that occurs with each footfall. So the work done in each stride is proportional to your weight and the change in height. If you had the patience to run in place for the same length of time that you run on the road, I think you would burn nearly the same amount of calories. But if you think running on a track is boring, this is far worse.

-----Original Message-----
From: phys-l-bounces@carnot.physics.buffalo.edu [mailto:phys-l-bounces@carnot.physics.buffalo.edu] On Behalf Of Stefan Jeglinski
Sent: Friday, April 17, 2009 9:20 AM
To: Forum for Physics Educators
Subject: Re: [Phys-l] Food Liar's calorie chart

> One can further estimate that 200lb displaced over a mile is
1,056,000 ft-lbs, or 342 nutritional calories (according to one
on-line calculator), yielding a factor mu (F = mu.N) of .43 for
> jogging, and .29 for walking.

Equating body weight with force in the direction of displacement
is suspect on the face of it.

How so? We do it all the time to incorporate friction in kinematics
(factor mu, normal force [weight], direction in the line (albeit
against) of displacement). Here the dominant effect, to get the
walker walking or the jogger jogging, is friction of the shoes
against the walking/running surface.

I have also read suggestions that the energetic cost of moving is
proportional more to time than to distance, so that I read of folks
being encouraged to walk at any speed for set time periods
as a slimming strategy.

I've gathered that this is due to the mantra that aerobic exercise is
better for slimming strategies, and that certain windows of duration
are optimal. In the end though, it is F.x that determines the amount
of energy expended.


Stefan Jeglinski
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