Thank you to everyone who entered our Fermi Estimation Contest this past January. Congratulations to winner Alex D, who received a free copy of How Many Licks? Several contestants asked for my solution, so I’m posting my results below:
How many snowflakes are in this snowman?
V = (4Pi / 3)*(R13 + R23+R33) ~ 1.6m3
From Hypertextbook.com, there are roughly 100 crystals per snowflake and 1018 molecules per crystal. One water molecule weighs 2.992x10-26 kg. From these facts, we can calculate the mass of a flake:
(100 crystals per flake)
*(1018 molecules per crystal)
*(2.992x10-26 kg per molecule)
3.0x106 kg per snowflake
According to Wikipedia, the density of snow varies considerably from 8% the weight of water for newly fallen snow, to 30% after it settles, to 50% in late spring. Since the density of water is about 1000kg/m3 and the snowman is pretty densely packed, I chose 500 kg/m3.
Using these numbers, we can calculate the number of snowflakes:
(1.6 m3)*(500 kg per m3) / (3.0x106 kg per snowflake) ~ 2.7x108 snowflakes