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Orchid XP v8 wrote:
> According to the textbooks, it takes 1 Jule to move a 1 kg object a
> distance of 1 meter.
If one Newton force is applied in the direction of motion for the whole
distance, yes.
> On the other hand, once the object has been moved, keeping it stationary
> requires no energy at all. And, indeed, if you take a lump of metal and
> put it on your bookshelf, it requires no energy to make it remain there.
> It just sits there like a lifeless lump of metal.
Quite true.
> Now, here's the thing: How much energy does it take to hold a 1 kg lump
> of metal at arm's legnth?
>
> According to physics, it would require 0 Jules.
If this were true, then it would take no effort to do this. You concept
of this being "according to physics" is off a bit.
> However, to keep the
> object stationary against the force of gravity, the muscles in your arm
> are having to continually expend chemical energy.
This is because the 1kg object is resting on a system of tensed muscles,
instead of a rigid framework. The tense muscles expend energy in order
to maintain their tension.
> But how the **** do you compute how much energy that is??
Exercise physiologists would probably measure the oxygen consumption of
a person at rest vs. a person holding the weight at arm's length. The
difference corresponds to the extra requirements.
Regards,
John
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