🚀 go-pugleaf

According to one local geology expert Fermi's question about the NUMBER OF
GRAINS on all beaches of the world can not be answered precisely till the term
"beach" is defined. The sand of a beach (be careful how you say it) is that
sand which is frequently washed away and redeposited by wind and water (at
least once every 100 years or so). His educated guess turned out to be about
two orders of magnitude larger than mine (2*10^21 versus 10^19 grains). But
he would not bet his life on that either. What is your number?

You may be interested that the factor of 8 difference, between the two
estimations, has to do with the sizes of representative grains (1 mm from
me and 1/2 mm from him). The rest has to do with his guess that the total
length of shores is ten times the circumference of the earth and that 75%
of shores are beaches whose representative width and depth are 60 meters and
10 meters respectively. But a second geology teacher came with a different
answer; it was only about ten times larger than mine.

I plan to bring this problem to a class; Fermi's method is worth discussing
with all students. A long list of questions suitable for practicing the "art
of estimations", has been compiled by Joe Bellina (jbellina@saintmarys.edu);
I think he will be glad to share it with you.

            Ludwik Kowalski     kowalski@apollo.montclair.edu