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Questions tagged [fermi-problem]

Fermi problems are questions where rough answers can be estimated from basic principles using little information.

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Entrainment of air and timekeeping of a mechanical watch at high altitude (problem attributed to A. H. Compton)

S. K. Allison told1 this Fermi problem: During the war, Professor A. H. Compton, Enrico Fermi, and I [Allison] were traveling together to visit the Hanford Plutonium Plant in the state of Washington. ...
Alessandro Jacopson's user avatar
3 votes
4 answers

How much gravity to make lead flow?

Lead is solid at room temperature. But it is quite soft, so under strong enough gravity, it should be possible to pour it out of a container like sand. What gravity is that? Let's do a Fermi estimate. ...
SCH's user avatar
  • 132
29 votes
4 answers

How many of the molecules that you inhale in a breath did Caesar exhale in his dying breath, on average? - Does this question make physical sense?

There is a nice example of a Fermi estimation question where you ask: How many of the molecules which Julius Caesar (or Jesus, Muhammad, etc. — anyone who died a long time ago) exhaled in their dying ...
0x539's user avatar
  • 695
2 votes
0 answers

Fermi estimate for ice nucleation timescale

My friends in a Cryo-EM lab freeze their very samples quickly, a process they call vitrification. The timescale for this process is milliseconds (from wikipedia): The production of amorphous ice ...
Hooked's user avatar
  • 431
3 votes
1 answer

Is there a Fermi estimations toolbox?

I am a theoretical physics student and am a little ashamed at my inability to estimate any measurable quantity. I would like to develop my skills at Fermi estimations. Although it is hopeless to ...
10 votes
1 answer

How efficient is the Crookes radiometer?

I remember many years ago, I think at 8th grade, seeing the teacher show us a Crookes radiometer. I remember it being very fascinating. Today I read the wiki article on it, after looking up what it ...
Valtteri's user avatar
  • 359
12 votes
3 answers

How did Enrico Fermi calculate the classical Fermi Problem?

From Wikipedia: Fermi was known for his ability to make good approximate calculations with little or no actual data, hence the name. One example is his estimate of the strength of the atomic bomb ...
Halfdan Faber's user avatar
7 votes
2 answers

A Fermi-question: Are there more stars than grains of sand?

This claim is pretty popular in the web and obviously cannot be answered by counting grains or stars. Thats what physicists call a Fermi-question. It deals with problems/questions where we dont have ...
Hauser's user avatar
  • 711