## Saturday, August 18, 2012

### A Question from Ninja Brian

Today's question comes from physicist Brian Wecht. Brian is co-founder of Story Collider, a podcast that shares people's personal stories about how science has affected their lives. Brian is also a member of Ninja Sex Party.1

Here's a picture of Brian in ninja form:

 Brian's a very good ninja.

What is the weight of all the facial hair grown by the world population of men on a given day? If you concentrated all that hair into one curly, villainous moustache, how long would that moustache be?
If I go a week without shaving, I'll have about half a centimeter of facial hair, which means my hair grows about 0.1 centimeters per day. Follicles are separated by about 1.0 millimeter, and they span an area of roughly 100 square inches.  Assuming each hair has a thickness of 0.1 millimeters and the same density of water at 1.0 grams per cubic centimeter, I would grow about 60 milligrams of facial hair each day.

For simplicity, I'll consider myself to be a typical man. This is not necessarilly a safe assumption however, since, follically speaking, I'm much more Wolverine than Bieber. Still, it should be a safe assumption for an order of magnitude estimate. If that's the case and we assume 20 percent of the world population (~1.4 billion people) are facial-hair growing men, then the total weight of facial hair grown on a given day would be about 90 tons.

This brings us to the second part of Brian's question: How long of a villainous mustache can we make?

 Ninja Brian will save us from this dastardly villain.
Mustaches take up much less area than beards. If you glue all the beard hair grown in one day to the ends of the mustache hair grown in one day, it would be as if the mustache grew about four times faster than normal, which amounts to roughly 0.4 millimeters of growth each day. Spread out over the 1.4 billion facial-hair-growing men, that would give a villainous mustache that's about 350 miles long. Snidely Whiplash would be proud.

Thanks for a great question, Brian!

Aaron Santos is a physicist and author of the books How Many Licks? Or How to Estimate Damn Near Anything and Ballparking: Practical Math for Impractical Sports Questions. Follow him on Twitter at @aarontsantos.

[1] Somehow how I'm super happy that the blog has gone from a Nobel Laureate to a member of Ninja Sex Party.