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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