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Energy in a human body. 
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#1
Jul1609, 08:16 AM

P: 96

I only have a basic knowledge biology, but I've wondered about this before.
From a "fully charged" adult male human to dying of lack of nourishment; in case of chemical energy from food, this is often said to be three weeks. If it takes that long for a human to lose energy, how much is held chemically, in joules? It's hard to believe that a human can keep moving for that long with the reserves we have. There's also the energy we gain with each breath, so that's a factor too. Also, if this chemical reserve was used up all at once in a single movement, how much more powerfully would our muscles fire (ignoring inhibition which stops the body from tearing it's own muscles, but then this a hypothetical of the force produced.) If an Olympic Athlete was able to use ALL of the energy to high jump, how far would he or she fly? (taking the destruction of the bone and muscle out of the equation). 


#2
Jul1609, 08:46 AM

P: 15,319

What we gain is oxygen, which allows us to burn the fuel that we eat. 


#3
Jul1609, 08:57 AM

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You can get a very rough first order approximation by starting with the average power output of an average human, which is roughly 200 watts. Given three weeks = 1,814,400 seconds, you get ~363 MJ.



#4
Jul1609, 09:03 AM

P: 96

Energy in a human body.



#5
Jul1609, 09:21 AM

P: 15,319

In electronic component cleanrooms, minute temperature changes can affect deposition rates of chemicals. The temperature of the room is so carefully controlled that, when employees enter and exit the room, they turn off or on a 60W light bulb to compensate. 


#6
Jul1609, 09:58 AM

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#7
Jul1609, 04:55 PM

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#8
Jul1609, 06:35 PM

P: 2,157

Another way to make a very rough estimate is to assume, say, 40 kg weight loss before death. If you divide 40 kg by the average atomic mass we get the number of atoms. If we assume that the atomic mass is 12 u, then we arrive at the estimate of 2*10^27 atoms. If the energy yield per atom in the various chemical reactions is 1 eV, then the total energy is 320 MJ, which is quite close to the estimate by Negitron



#9
Jul1609, 06:38 PM

P: 2,157

I think there is a factor 4 efficiency factor between energy use and power. If you generate 200 Watt useful power on a home trainer, you are actually burning energy at a rate of 800 Watt.



#10
Jul1609, 06:49 PM

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Another orderofmagnitude estimate, based on calorie consumption. If an average person requires 2,000 calories per day, then he uses 2,000 C x 4,184 J/C x 15 days = 126 MJ. That's probably closer to the mark than my previous estimate, which is based on the derating value of a human's power output for HVAC system sizing.



#11
Jul1609, 07:26 PM

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The American Society of Heating, Refrigeration, and Air conditioning Engineers publishes energy consumption data for various activities for use by engineers. Thinking about it more, 70 watts is actually just the sensible heat  there's an additional somewhat lesser amount of latent heat (moisture) generated. For an office worker, it is something like 250 btu sensible, 200 latent. Anyway, sorry, 200 w wasn't far off the mark and is reasonable for someone doing some active housework or something like that. 


#13
Jul1609, 07:32 PM

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#14
Jul1609, 07:33 PM

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#16
Jan2711, 10:48 AM

P: 2

Hi,
I hope it's okay to bump this older thread. I'm a scifi writer. And I've been googling for information about the amount of energy in the human body so that I can flesh out a plot detail in my current novel. (Thus I landed here.) As background to my questions, here is an older science news article from the Sydney Morning Herald which points toward what I am writing about in my novel. http://www.smh.com.au/articles/2003/...849278131.html So ... my questions are: 1) How much energy does a GPS tracker need PER HOUR to transmit all day long? 2) How much energy does the human body generate PER HOUR via normal digestion of food? 3) How much of an energy deficit would that human suffer PER HOUR as a result of the GPS tracker stealing energy away from him? And would he need a daily allotment of extra food and more sleep to try and make up for that deficit? 4) I am very poorly versed in the technical jargon used when discussing electricity, wattage, amps, hertz, joules, etc, and I am equally inept at trying to translate back and forth between watts and amps and volts and hertz and joules, etc, so please give me the fordummies treatment if you launch into that sort of explanation. Thanks for all your help!! :) 


#17
Jan2811, 05:36 PM

P: 105

Power is energy per unit time. Watts are units of power, and 1 Watt = 1 Joule per second. Volts multiplied by Amps will give you Watts because the terms for electric charge in each unit will cancel each other out. Calories are units of energy, not power. If you convert 2000 Calories into Joules, then divide that number by the number of seconds in a day, the result will be in Watts. Remember that a lot of the energy is lost as heat (also Joules), so only a fraction of the 2000 Calories could be tapped into for "useful" work.



#18
Jan2811, 08:21 PM

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P: 5,523

2) the human body basically generates 100W of power from normal resting metabolism (normal recommended daily calorie intake). 3) The GPS transceiver draws a negligible amount of power when compared to this. You would not notice. 


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