# I didn't know that.

Discussion in 'Physics & Math' started by Bishadi, Mar 12, 2009.

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2,745
can anyone tell me what is wrong with this?

((2000 (kilocalories / day)) / (60 kilograms)) / ((400 yottawatts) / (2 * (10^30) kilograms)) = 8 070.98765

This above says that a pound of human flesh, produces more 'heat' than a pound of the sun (a star), by a factor of about 8,000

a mind twister for the day!

3. ### draqonBannedBanned

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35,006
the 400 yottawatts, explain this figure.

5. ### Idle MindWhat the hell, man?Valued Senior Member

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1,709
Where are you getting these figures from? Your units are all messed up as well. You have Calories on top, but Watts underneath?

7. ### TrippyALEA IACTA ESTStaff Member

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10,890
Yeah, the number's too low.

First off you've mixed up your units - in one place you're useing calories per day, in another place you're using joules per second.

2000 Kilocalories/day = 23.148 calories/second
23.148 calories/seconds = 96.8 watts.

So now that we're comparing apples with apples.

$\frac{\frac{96.8}{60}}{\frac{3.83x10^{26}}{1.9891x10^{30}$

Although really, we should be using the mass of the core in this, as that's where all the energy is generated.

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9. ### CranERegistered Member

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pound for pound the human body Does produce more energy than the sun. It's a fact.

10. ### PeteIt's not rocket surgeryRegistered Senior Member

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10,167
Actually, both consume energy and release heat, but I know what you mean.
And, it makes sense. The Sun is mostly blanket to keep it nice and warm in the middle where the important stuff happens. If a human were hanging about in space like the Sun is, they'd need a pretty hefty blanket as well.

Now, the Sun has a pretty good blanket (half a million km of hydrogen and helium), but bear in mind that it has to keep really warm (13 million °C warm).

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2,745

kind of neat to comprehend

just imagine teaching that to a young classroom and watch their little minds running with thoughts and ideas

bet the teachers would have a field day covering the questions

p/s................. the math is correct!

seems anyone who did not see it, was not up to speed on how to work through it, as well no one can say it is not accepted paradigm..............because it was run, as it is, thru google!

12. ### TrippyALEA IACTA ESTStaff Member

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10,890
No, the math is not correct.
8300 ≠ 8070

13. ### dinosaurs!Registered Member

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Sorry to bump such an old thread, but I just found this while going through some of my old posts on another forum. I'm the one who did the calculation Bishadi quoted (with a little help from Google Calculator).

Google Calculator does automatic unit conversions, which is how I managed to get away with putting kilocalories per day on top and yottawatts on the bottom - they're both units of power and Google Calc does the annoying part of converting the measurements for me. The figures of 400 yottawatts (approximate power output of the sun) and 2*10^30 kg (approximate mass of the sun) were both pulled of Wikipedia, and I rounded them off to one significant figure because this was very much a back-of-the-envelope calculation. I know I also overestimated the heat output of the human body because not all the food energy we consume is metabolically converted into heat, but hey, laziness.

No, the math is not correct.
8300 ≠ 8070

Significant figures! I only used one. I'm guessing you used the raw data off NASA's website, which would explain the discrepancy.

Also, no love lost seeing Bishadi got banned here. The dude was ANNOYING.

14. ### TBodilliaRegistered Senior Member

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Are humans brighter than the Sun?

"The Sun’s volume is 1.4 x 1033 cubic centimeters. That means that each cubic centimeter gives off 4 x 1033 ergs/second / 1.4 x 1033 cc = 2.8 ergs/second/cc."
"Finally, dividing my luminosity by my volume yields 170,000 ergs/sec/cc."

"But hold on there. Is this really a fair statement?

Well, not really. First, there are a whole lot more cubic centimeters in the Sun (about 1028 times as many, or ten billion billion billion times as many), so when you divide by such a big number the energy per cc for the Sun drops drastically. So even if we say, sure, humans are more luminous per cubic centimeter, it’s best not to get cocky. The Sun can still vaporize us with lots of cubic centimeters left to spare.

Second, remember the assumption I made, that the Sun has the same temperature everywhere? That’s not even close to being true. In fact, it’s whoppingly untrue. The core of the Sun is 15 million Kelvins hot, so each cc there is blasting out vast amounts of energy: about 5 quadrillion times what a cc of human flesh does. But outside of that region the Sun is much cooler, and each cc doesn’t contribute nearly as much. Over the entire Sun, that dilutes the amount of energy per cc quite a bit. Averaging over the volume of the entire Sun is not a great way to think about it, and makes comparisons difficult, if not really meaningless."

It's the same as saying "On paper, a bumblebee can't fly."

15. ### CHRIS.QRegistered Senior Member

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Feeling it's exaggerated