Am 31.07.2010 22:36, schrieb Orchid XP v8:

>> 1 Joule is also the energy transformed in heat in 1 second by a 1 Ohm
>> resistor when the current is 1 ampere.
>
> And here I was thinking that the heat produced depends on the
> characteristics of the material, not just the current...

In a sense that's true - but the material characteristics influence the 
resistance /exactly/ the same way as the heat produced ;-)

> I guess ultimately, muscles generate forces. Presumably to hold an
> object still, the force generated by the total muscle system must be
> equal (and opposite to) the force of gravity. It's all quite
> complicated, since most forms of locomation involve levering, and you'd
> have to know muscle insertion points and pivot lengths and so on.

The thing with muscles is, they never actually hold something still 
unless they're totally slack. When they're contracted, they actually 
twitch at a high frequency, thus repetitively lifting the weight up a 
bit, converting chemical energy to potential energy, then letting the 
weight drop a bit only to catch it again a split second later, wasting 
some of the energy as heat. (The tendons help "recycling" some of the 
kinetic energy by converting it into mechanical energy like a spring, 
and kangaroos make pretty effective use of this mechanism for moving 
around, but even they lose part of the energy as heat, thus effecting 
global warming and ultimately the entropy death of the universe... but 
maybe I'm drifting off here :-).)

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