Your random physics thought for the day

(From a problem set my students just handed in…)

The amount of energy it takes to bring water from room temperature to a boil is enough to launch it 34km straight up. The amount of energy it would take to boil it down all the way – until it all evaporated – would launch it 270km.

Compare this to a typical altitude for a 747, about 11km, or for a space shuttle, about 150km.

Damn. Water has a very high heat capacity.

And the idea of launching a liter of water 34km into the air is pretty cool.

From a conversation last night, a suggested physics exam problem:

“(a) A whelk is a small mollusc, a kind of marine snail. Demonstrate quantitatively that a whelk would stand no chance in a supernova.

(b) Assuming that the whelk were on Earth and the Sun went nova, estimate how large the whelk would have to be in order to stand a chance. (You might want to imagine a case in which the Sun were about 3 times its actual mass, so that it could actually trigger a supernova on collapse)”

With no additional information given, this would actually be a pretty good question. Requires the ability to estimate physical properties of whelks and supernovae, and think about how they might interact. This is probably a bit too high-level for my freshmen, though, since they don’t have enough background yet to think meaningfully about supernovae. (Well, maybe a few of them do, but not enough to give this on the final)

This has been your random thought for the day.

Published in: on June 4, 2003 at 21:06  Comments (3)  


  1. A legendary Cambridge biology exam question asked the candidates to assess the feasibility of breeding bulletproof or bullet-resistant dogs.

  2. Here, let me estimate the interaction for you:
    whelk all gone

  3. Wow. I wonder what the answers were like…

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