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>> 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.
Yeah. It _is_ kind of conspicuous that all the examples talk about
*lifting* an object. As if moving an object horizontally wouldn't
require any energy or something...
> 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...
>> 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 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)
Mmm, interesting.
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.
I guess the really interesting question is, how much energy does it take
for a muscle to produce a given amount of force? (And, perhaps more
importantly, what variables does this depend on?)
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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