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discussion : 4c559d0e$1@news.povray.org...
> Sure. Now tell me how much energy is released by the production of 1 unit
> of CO2...
These kind of measurements are made in special boxes named metabolic
chambers. I've seen some made for pigs and cows but here's one for people
(with a real bed and all) :
http://labs.pbrc.edu/energymetabolism/MetabolicChambers.htm
G.
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And lo On Sat, 31 Jul 2010 15:21:31 +0100, Orchid XP v8 <voi### [at] dev null>
did spake thusly:
> 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??
To ask it another way how much energy is the bookshelf using to keep the
lump of metal from falling through it under the influence of gravity ;-)
--
Phil Cook
--
I once tried to be apathetic, but I just couldn't be bothered
http://flipc.blogspot.com
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Phil Cook v2 wrote:
> To ask it another way how much energy is the bookshelf using to keep the
> lump of metal from falling through it under the influence of gravity ;-)
That's really not the right way to ask the question. The right way to ask
the question is how much more work can the lump of metal do after sitting on
the bookshelf (or in your hand) for 30 seconds? It hasn't anything to do
with how much effort it takes to hold it. It has to do with the final
resulting configuration.
--
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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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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clipka <ano### [at] anonymousorg> wrote:
> 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 ;-)
>
Heat is heat is heat. If heat is generated, heat is generated. Don't confuse
that with _temperature_ . The temperature that objects rise to will depend on a
number of properties, starting with _heat_capacity_ and eventually influenced
by _thermal_conductivity_ , convection currents in the neighborhood, etc.. A 1
Ohm aluminum and 1 ohm tungsten wire will warm up differently, even if the same
heat were generated.
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Am 02.08.2010 22:32, schrieb gregjohn:
> clipka<ano### [at] anonymousorg> wrote:
>> 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 ;-)
>>
>
>
> Heat is heat is heat. If heat is generated, heat is generated. Don't confuse
> that with _temperature_ . The temperature that objects rise to will depend on a
> number of properties, starting with _heat_capacity_ and eventually influenced
> by _thermal_conductivity_ , convection currents in the neighborhood, etc.. A 1
> Ohm aluminum and 1 ohm tungsten wire will warm up differently, even if the same
> heat were generated.
Don't worry, I'm not confusing these things here. I guess Andy has
gotten the point I intended to make: "Sure, there are experimental
setups where the heat generated by a sample resistor at a given current
depends on the material characteristics - but you're forgetting that
those experiments don't have a constant resistance either."
Not really contradicting what you say, is it?
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Am 02.08.2010 18:22, schrieb gregjohn:
> I guess I've run out of my area of expertise to say anything more about
> that.
Duh - since when does one have to have /expertise/ to contribute to a
topic here? :-P
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> 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??
If your heart rate monitor shows calories burned then just use this (with
and without the object), should give a rough approximation.
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scott 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??
>
> If your heart rate monitor shows calories burned then just use this
> (with and without the object), should give a rough approximation.
And then you have to wonder, how the hell can the heart monitor
determine how many calories you're burning just from your heart rate?
--
http://blog.orphi.me.uk/
http://www.zazzle.com/MathematicalOrchid*
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> And then you have to wonder, how the hell can the heart monitor determine
> how many calories you're burning just from your heart rate?
Presumably it just has some kind of lookup table or formula based on heart
rate, age and weight (assuming you entered those values, I had to on mine),
taken from actual experiments on humans.
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