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This question was asked on Judaism.StackExchange a few days ago, but I think it has a better chance of being answered here.

Disregarding the grammatical discussion in the comments on that question1, Rashi (a commentary on Bible) wrote that if you hollow out an eggshell, fill it with dew, close it, and leave it out in the sun, the eggshell will rise in the air.

Question: will an eggshell, filled with dew and heated, actually rise in the air?

Apparently, someone tried this out, and found that the eggshell rose a few centimeters. (Page is in Hebrew, Google Translate does an OK job, but everything you really need to know is copied here.)
Also found this type type of thing discussed (though with a different starting point) here.


1 FTR, I actually think that he was referring to the dew, but let's look at this question as if he was talking about the eggshell.

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  • $\begingroup$ What if you hollow it out, seal it on a hot day and wait for the dense cool air at night to elevate it like a balloon. I still don't think there would be enough density difference to overcome the weight of the shell. $\endgroup$ – ja72 Jul 10 '14 at 17:41
  • $\begingroup$ @ja72 I don't know .... maybe toss that out as an answer, see what the community thinks of it through votes? $\endgroup$ – AnotherUser Jul 10 '14 at 17:44
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What is probably being referred to here indirectly is the fact that air with moisture in it is less dense that dry air. The question becomes, is the buoyancy force of an empty egg with the optimal moisture content of air sufficient to overcome it's weight?

Searching around I see that water vapor has a density of 0.804g/Land dry air has a density of 1.27 g/L. So from that I will revise my interpretation of the question.

Will an empty eggshell full of water vapor rise at STP?

Volume of an egg = 52 ml, therefore weigh differential is (1.27-0.804)*0.052 = 0.0242 grams.

With an egg shell typically taking up 11% of the weight of an egg (being 50 grams), and 11% is 5.5 grams.

TLDR: No

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    $\begingroup$ You know way too much about eggs :-) $\endgroup$ – ja72 Jul 10 '14 at 18:05
  • $\begingroup$ Interesting....althought, this is calculated at STP; Rashi lived in Troyes, France....could there be different pressure there than is considered standard? (IIRC the go-to example in my physics class for different pressure was south of France; Troyes is in northern France) $\endgroup$ – AnotherUser Jul 11 '14 at 13:05
  • $\begingroup$ Wolfram Alpha gives STP pressure as 101.3 kPa (as it should be); standard pressure in Troyes they give as 101.6 kPa ....is that significant enough to make a difference? $\endgroup$ – AnotherUser Jul 11 '14 at 13:08
  • $\begingroup$ @AnotherUser Nope, there is at least 2 orders of magnitude separating the buoyancy force vs the shell weight. $\endgroup$ – placeholder Jul 11 '14 at 14:13
  • $\begingroup$ The critical parameters seem to be the volume of the egg and the mass of the shell. On page 321 of this article the volume of different eggs is tabulated. In the table "Shell weight vs egg weight" in this article you have the shell weight. Now is it possible to guess which sort of egg might work this trick? $\endgroup$ – Avrohom Yitzchok Feb 9 '17 at 21:25
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No. For the same reason that you can't pick yourself up by your shoelaces. However, if you were to fill a container with water and close off the escaping steam with the eggshell, it would be possible to "levitate" the eggshell with the rising steam.

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