This Homework is now due Friday, September 16, 2011

Estimate the maximum number of hairs someone can have on his or her head. Explain how you obtain your estimate.

You can use the method discussed in class. Assume heads are never bigger than a basketball. Find the radius R of a basketball (in millimeters say). The surface area (in square millimeters, or mm2) of the basketball is then 4(Pi)R2, where Pi is about 3.1416.

The diameter of a cross section of a human hair is about 0.017 mm, thus the area taken up by a hair on someone's head is at most (Pi)r2, where r = 0.017/2 mm. Now you can find how many hairs could fit on a basketball and thus a maximum number of hairs that can fit on someone's head. What number do you get?