Le 31/07/2010 16:21, Orchid XP v8 nous fit lire :
> According to the textbooks, it takes 1 Jule to move a 1 kg object a
> distance of 1 meter.

Objection. It (1 Joule) is the work of a Force of 1 Newton whose point
of application is moving by a distance of 1 meter along the direction of
the force.

1 kg is a mass, not a force. Your planet might influence the number of
Joule to move such a mass.

1 Joule is also the energy transformed in heat in 1 second by a 1 Ohm
resistor when the current is 1 ampere.

> 
> 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??
> 
According to physic, the global work is null.
What are the forces:
 - gravity, F= 1*g Newton (g ~ 9.81 ?) for the lump of metal, vertical,
downward
 - gravity on your arm, vertical, downward
 - muscles on the shoulder, vertical, upward when converted from couple.

What is the weight of your arm ?
What is its length ? (we have a couple to nullify to reach static)
(we assume so far the other joints of the arms are locked by the bones &
position, it might be different and might introduce more forces)

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