I love learning new things to do with a laser pointer. (Usually I just blind people. That gets old.) This cool short video shows you how to measure the width of a human hair.
This three-minute video, enlivened by footage of one scientist yanking the hair out of another scientist's head, shows you how to measure the width a human hair. By using a human hair to bisect the beam of a laser pointer, the scientists set up a diffraction pattern. After measuring the distances between the light and dark spaces on the diffraction pattern, the distance from the hair to the wall, and the wavelength of the laser, they are able to use simple multiplication and division to figure out the diameter of the hair.
I don't see any reason to stop there, though. Since this will get you the diameter of nearly any small object, try measuring the hair of your loved ones, pets, and strangers on the street. (Perhaps you should confine yourself to only strangers that you are confident you can outrun.)
[Via Jefferson Lab.]