It's a simple question, but requires one to sharpen one's physics vocabulary
greatly in order to answer it.

First of all, the missing concept in your question is WORK.  There is zero work
required if one were to hold an object stationary against a force.  Work is
force times distance. If you lift an object, you do the work of force x distance
and increase its gravitational potential energy.  Again, holding it stationary
is zero work.

It may be ironic that it still takes "effort" on your muscles' part to hold it
still, even if they do no work. Perhaps it helps to think of how athletes engage
in weightLIFTING, not weightHOLDING.  There's more exercise in the WORK.

Just typing here: putting a 20 pound, expertly-designed backpack on my back
isn't as much "exercise" as is holding a 2 pound weight at arms length.  And the
latter hurts your muscles more because of the fulcrum-- you've got to put a huge
force on one side of the fulcrum's short arm inside your body in order to
balance out the small force held out at the (literally) long "arm".  In the case
where your arm shakes, you may do work up and down over and over, getting more
tired.

But will you burn more calories by holding that weight at arm's length? I'm
sure. I guess I've run out of my area of expertise to say anything more about
that.



Orchid XP v8 <voi### [at] devnull> wrote:
> According to the textbooks, it takes 1 Jule to move a 1 kg object a
> distance of 1 meter.
>
> 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.
>
> 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. However, to keep the
> object stationary against the force of gravity, the muscles in your arm
> are having to continually expend chemical energy. But how the **** do
> you compute how much energy that is??
>
> --
> http://blog.orphi.me.uk/
> http://www.zazzle.com/MathematicalOrchid*

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