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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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On 31/07/2010 3:21 PM, Orchid XP v8 wrote:
> 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??
Analyse the system and come back with an answer. This is 3rd year high
school mechanics.
--
Best Regards,
Stephen
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Stephen wrote:
> Analyse the system and come back with an answer. This is 3rd year high
> school mechanics.
Riiiight. Too bad I didn't do that class, eh?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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On 31/07/2010 3:54 PM, Orchid XP v8 wrote:
> Stephen wrote:
>
>> Analyse the system and come back with an answer. This is 3rd year high
>> school mechanics.
>
> Riiiight. Too bad I didn't do that class, eh?
>
Well use your big brain and work it out from first principles
--
Best Regards,
Stephen
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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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Le_Forgeron <jgr### [at] free fr> wrote:
> According to physic, the global work is null.
At least according to newtonian physics. I'm wondering if general
relativity muddles this because it says (and there's rather compelling
empirical evidence that GR is right in this) that the object sitting on
the shelf is actually in a constant state of acceleration (while, perhaps
rather ironically, a free-falling object is not, which is kind of the
complete reverse of what newtonian mechanics says).
It's curious, even though I have read quite some material about both
newtonian mechanics and both theories of relativity, it's still unclear
to me how the "traditional" postulates of newtonian mechanics (such as
the quintessential "F=ma" and other such basic formulas) work when we
take general relativity into account (especially when we are talking
about gravity rather than simply forces applied to objects floating
in zero gravity).
In classical newtonian mechanics the total amount of work performed
on an object on the floor is zero, but is it also in general relativity?
How does GR affect this? Or does it affect at all?
--
- Warp
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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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On 31/07/2010 9:36 PM, Orchid XP v8 wrote:
> 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...
>
That is because it is the simplest to describe. When you master this we
will move on to friction on a horizontal plane then an inclined plane.
>> 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...
>
The characteristics of the material is reflected in the resistance or
vica versa.
>> 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?)
>
You are getting there :-D
--
Best Regards,
Stephen
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"Stephen" <mca### [at] aolDOTcom> wrote in message
news:4c54356b@news.povray.org...
> On 31/07/2010 3:21 PM, Orchid XP v8 wrote:
> > 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??
> Analyse the system and come back with an answer. This is 3rd year high
> school mechanics.
The question has almost nothing to do with mechanics *or* high school. It's
biological/physiological and dependant on many complex factors. You almost
never compute such things by "analysing the system" and working from basic
principles, but you make empirical measurements.
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Orchid XP v8 wrote:
> 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...
It doesn't, in the physics definition of "energy". Other than the fact that
you expend energy to accelerate the object and more energy to decelerate it,
and to overcome friction and such. But if it's (say) sitting on a
frictionless surface, you can move it as far as you want with as little
energy as you want.
You're thinking the physics definition of "energy" has something to do with
"effort". The physics definition of "energy" has to do with how much work
you can make the mass under consideration perform. I.e., if it's the weight
on a pendulum clock, and the clock is stopped because you're holding it up,
you're neither making the clock capable of running longer nor shorter
because you're holding it.
--
Darren New, San Diego CA, USA (PST)
C# - a language whose greatest drawback
is that its best implementation comes
from a company that doesn't hate Microsoft.
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