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Q: How much energy does the human body radiate ( No Answer,   17 Comments )
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 Subject: How much energy does the human body radiate Category: Science Asked by: gillwill-ga List Price: \$2.00 Posted: 23 Feb 2006 10:26 PST Expires: 25 Mar 2006 10:26 PST Question ID: 448894
 ```I am interested in learning how much energy, in wattage, is radiated from the human body, and what the various forms of that radiation are: e.g. electric, thermal, (other particles?) I have come across articles here and at other web sites on the energy of the human body but they seem to refer more to energy generating within the body, whereas I'm interested in that which is emitted from the body. I appreciate any insights on this topic.```
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 Subject: Re: How much energy does the human body radiate From: probonopublico-ga on 23 Feb 2006 10:49 PST
 ```You'll find a lot of stuff by searching for: Kirlian Aura Photography. Good luck!```
 Subject: Re: How much energy does the human body radiate From: siliconsamurai-ga on 23 Feb 2006 11:16 PST
 ```It depends on the person, level of activity, etc. but the obvious answer is about 2200 cal. per day since that is the energy input needed to maintain the average person's weight. Consume more than 2200 cal. you gain weight, less, you loose. Of course that is just an average.```
 Subject: Re: How much energy does the human body radiate From: siliconsamurai-ga on 23 Feb 2006 11:17 PST
 ```BTW, any energy generated is also radiated if the body temperature remains the same - extremely basic science.```
 Subject: Re: How much energy does the human body radiate From: jack_of_few_trades-ga on 23 Feb 2006 11:59 PST
 ```Silicon, I'm curious if expending energy by using muscle or by excretion is considered "radiating" in your answer. I'd like to think that all the calories I eat aren't going directly to keeping my body temperature constant. But I could be thinking about this incorrectly. My thought of Gillwill's questions is that he's interested in how much energy radiates (in the form of heat perhaps) from the body. My guess is that this is a very different answer than how many calories we eat.```
 Subject: Re: How much energy does the human body radiate From: rracecarr-ga on 23 Feb 2006 13:01 PST
 ```The total amount of radiation coming from your body is determined very simply from the surface temperature of your body and the surface area by the Stefan-Boltzman Law, which says that total energy radiated by a blackbody per unit area per unit time is sigma*T^4, where sigma is the Stefan-Boltzman constant, 5.67E-8 J K^-4 m^-2 s^-1, and T is the temperature in Kelvin. So if you have a surface area of 1 m^2 and a surface temperature of 310 K, you radiate at a rate of a little over 500 Watts. That means that you would have to eat over 10,000 Calories per day just to maintain your temperature. No one eats that much, so what gives? Well, most importantly, your body is constantly absorbing radiation as well as emitting it. If you were thrown naked into a freezer with a temperature close to absolute zero, you really would radiate at a net rate of about 500 Watts (for a short time). But usually, things around you are warmer than that, and so they radiate too, and you absorb some of that radiation. Also, your effective surface temperature is the temperature of your clothes, which is less than your skin temperature. Anyway, the absolute rate at which your body radiates is in the neighborhood of 500 W, but the net rate is much less, and depends on your temperature relative to your surroundings. 50 to 100 W is probably not a bad guess.```
 Subject: Re: How much energy does the human body radiate From: siliconsamurai-ga on 23 Feb 2006 13:43 PST
 ```Jack, ANY energy generated by the body is eventually radiated or your temperature goes up, simple thermodynamics, you can also attempt to measure every single adenosine tri phosphate and other chemical reaction in the body, but overall, calories consumed/absorbed = calories radiated or expelled, otherwise temperature goes up. Your muscle movement MUST generate heat if it uses energy, which MUST be radiated or otherwise expelled or exchanged via conduction. Since even conduction is probably going to end up mostly as IR radiation, it is all the same, but this is just a comment, not a detailed answer to your question. You asked for any insights and those are the ones of a physicist. BTW, at least 99% of the radiation will be thermal, possibly 100%. Good question by the way.```
 Subject: Re: How much energy does the human body radiate From: qed100-ga on 23 Feb 2006 17:30 PST
 ```As I recall, a typical healthy adult human generates in the neighborhood of 90 watts.```
 Subject: Re: How much energy does the human body radiate From: sobinator-ga on 23 Feb 2006 18:32 PST
 ```in one hour, your heart works hard enough to produce the equivalent energy to raise almost 1 ton of weight 1 yard off the ground. (http://www.coopsjokes.com/amz/amzbody.htm) ...allow a person to pump out 100 watts - enough to illuminate a light bulb. (http://www.smh.com.au/articles/2003/08/03/1059849278131.html)```
 Subject: Re: How much energy does the human body radiate From: kottekoe-ga on 23 Feb 2006 21:33 PST
 ```I beg to differ with the thermodynamics conclusion. There are other ways to release energy. The work you do with your muscles releases energy. For example, if you throw a ball, you can subtract the kinetic energy of the ball. If you climb stairs, you can subtract the change in gravitational potential energy. Also, you expel thermal energy with each breath of hot air, and the chilling wind that blows by you carries away hot air. Still, the loss due to radiation is real and important.```
 Subject: Re: How much energy does the human body radiate From: siliconsamurai-ga on 24 Feb 2006 13:07 PST
 ```kottekoe when you're right, you're right.```
 Subject: Re: How much energy does the human body radiate From: knickers-ga on 27 Feb 2006 06:22 PST
 ```We have often toyed this one over in the office. One of our engineers is a thermodynamic engineer. He came to the conclusion that if we all walked around naked and ate the same food we would loose weight due to increased dissipation of energy by radiation. He did calculate it out once and I think he came to a figure of about 200W as a rough estimate. You only have to get 10 people in a small room and it gets fairly hot fairly quickly. Energy is never created or destroyed so if you consume it you must use in one way or another. You either conduct it or radiate it. Re your example of the ball. You impart energy to the ball but it comes from somewhere i.e. your muscles which burn and loose some more energy in the effort plus a few efficiency losses.```
 Subject: Re: How much energy does the human body radiate From: probonopublico-ga on 27 Feb 2006 11:19 PST
 ```Knickers wrote: He came to the conclusion that if we all walked around naked ... Oh yes! I bet he just wanted you to get your knickers off.```
 Subject: Re: How much energy does the human body radiate From: siliconsamurai-ga on 03 Mar 2006 09:30 PST
 ```Perhaps I should point out that WORK, such as lifting or throwing, actually uses very, very little energy for most people. That is why you have to exercise so much to make up for eating pie.```
 Subject: Re: How much energy does the human body radiate From: matus1976-ga on 13 Mar 2006 13:53 PST
 ```Well since I apparently can not sign up to answer questions here is an answer for free The following excerpts are from LIVING IN SPACE by G. Harry Stine 4 - Keeping Cool "At rest, the human body gives off nearly 1,600 calories per minute. During active periods, the thermal output jumps to about 2,900 calories per minute. In comparison, the human body gives off about as much heat as a 100 watt light bulb. It's easy to understand, therefore, why a room full of people grows warm just from the accumulating body heat of everyone there" pg 49 "When resting, about 78 percent of the heat is given off by normal heat transfer processes such as conduction, convection, and radiation. 22 percent is given off by the evaporation of perspiration. While working, 45 percent of the heat is lost by normal heat transfer methods and 44 percent through perspiration. The remaining 11 percent goes toward the actual accomplishment of physical work. Calculations based on these numbers indicate that the human being is approximately 11 percent efficient or about as efficient as an internal combustion gasoline engine" pg 50 9 - WORKING IN SPACE "During sleep, the body's energy expenditure is about 65 Calories (kCal) per hour. At rest lying down, it rises to 80 kCal/hr and, when sitting up, to 100 kCal/hr. During light exercise, this jumps to as much as 200 kCal/hr and, during heavy physical work, to 500 kCal/hr. Under normal conditions the human body is only 11 percent efficient as a heat engine. This means that 89 percent of the metabolic heat output shows up as increased perspiration rate, increased respiration, and slightly elevated body temperature" pg 135 [65 Cal/hr --> 500 Cal/hr] "But any life support system for small space cabins and space suits must also have adequate reserve capacity to handle the times when space workers are dumping as much as 400 kCal/hr or more into the immediate environment" pg 135 "Advanced space suits may not be tailored to specific users as NASA space suits are. Like clothing, they will come in standard sizes--perhaps small, medium, and large. They will also have the life-support capacity to handle 500 kCal/hr for at least an hour, which is the length of time an average person can work at the heat expenditure rate of 500 kCal/hr. The life support system is contained in a backpack because it can't be distributed around the space suit and because the backpack interferes least with the weare'r movements and working activities. The space suit must also be easy to get into and out of like the NASA space-shuttle suit. Ease of donning a space suit is critical in an emergency." pg 136 8 - Nutrition and Sanitation "The average adult human body requires between 1,800 and 3,600 kilo-calories per day. The minimum acceptable caloric intake is about 1,600 calories per day on a long term basis...The normal daily caloric requirement for male adults is 21 Calories per pound of desired body weight, while the adult female is 18 Calories per pound. Young, growing humans often require as much as twice the normal daily caloric intake." pg 111 NOTE --> kCal = KiloCalories. 1 food calorie = 1,000 physics calories, or 1 kCal. Hope those help! Matus```
 Subject: Re: How much energy does the human body radiate From: robjewell-ga on 19 Mar 2006 19:28 PST
 ```"What gives" rracecarr-ga is that when you see Calories (capital c) on a bag of potato chips, what they mean is 1000 calories (lower case c, Kcal.). So, an average person needs 2,200,000 calories per day, not 2,200. Alas it weren't so, I'd drink ice cold beer all day to loose weight. After all it takes 4,260 calories to raise the emperature of a 12 oz. beer 1 degree Celcius. Thats 157,620 calories to raise a beer from freezing to body temp.```
 Subject: Re: How much energy does the human body radiate From: robjewell-ga on 19 Mar 2006 19:29 PST
 ```Also, no animal's system is more than about 10% efficient. Most of the energy you eat is passed without being used by the body.```
 Subject: Re: How much energy does the human body radiate From: rracecarr-ga on 27 Mar 2006 15:07 PST
 ```robjewell: I am aware of the difference between calories and Calories. I was using the 'potato chip' unit (big C) in my earlier comment, and 500 W is roughly 10,000 Calories/day. Also, your beer math is off: it takes about 13,000 calories (not 157,620) to raise the temperature of a beer from 0 to 37 degrees Celcius.```
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