The Mystery of Human Luminosity: A Comparison to Daily Energy Intake

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The discussion explores the calculation of human luminosity, assuming the body radiates like a black body at a temperature of 310K, resulting in a luminosity of 733 watts. This is contrasted with the daily energy intake from food, approximately 3000 calories or 12500 joules, leading to the observation that humans radiate more energy than they consume. The conversation raises questions about the apparent discrepancy in energy balance and compares this to a rock, which maintains a stable temperature without energy intake. Additionally, it highlights the different meanings of "calorie" in scientific versus everyday contexts. The thread emphasizes the need for clarity in understanding energy dynamics in living organisms.
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Homework Statement


If we assume that a human radiates like a black body, calculate the luminosity in watts, then compare it to the daily energy a human gets from eating. (The area of a human A=1.3 m2)

The Attempt at a Solution


The temperature of a human is 310K so L=AσT4 = 1.4*5.6*10-8*(310)4=733 watts and the average energy of a human gets from eating is about 3000 calories=12500 joules.
So in one day a human seems to radiate too much energy compared to the daily energy he gets. What is going on?
 
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Xalkias said:
What is going on?
Let's say you're not looking at a human, but at a rock. It gets zero Joules from eating. How come it stays at a comfy 30-ish degrees centigrade on a warm day?
 
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Xalkias said:
...3000 calories=12500 joules.
... What is going on?
Along with paying attention to Bandersnatch's comment, you might also want to look into the sciency vs laymanish use of the word "calorie".

hint: They have two different values.

ps. I'm going to ignore your "area" typo, as it's not that big a deal.
 
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