Isotope analysis
A recent development in forensic science is the isotopic analysis of hair strands. Hair has a recognisable growth rate of 9-11mm per month or 15 cm per year. Human hair growth is primarily a function of diet, especially drinking water intake. The stable isotopic ratios of drinking water are a function of location, and the geology that the water percolates through. Sr, Sr and oxygen isotope variations are different all over the world. These differences in isotopic ratio are then biologically 'set' in our hair as it grows and it has therefore become possible to identify recent geographic histories by the analysis of hair strands. For example, it could be possible to identify whether a terrorist suspect had recently been to a particular location from hair analysis. This hair analysis is a non-invasive method which is becoming very popular in cases that DNA or other traditional means are bringing no answers.
Ponytail
The numerical values used in this equation were the average density of human hair (1.3 grams per cubic centimeter), a bending modulus ( "A" ) of 8 × 10 Newton meter, a linear mass density of hair ( "λ" ) of 65 micrograms per centimeter and the major diameter of the hair (human hair is elliptical in cross section) of 79 ± 16 micrometers. "N" was taken to be 100,000 - the average numbers of hairs on a human head. The constant "E" was that of nylon which is similar to hair in its bend and twist moduli. The length "L" was taken to be 25 centimeters. These values give a length at which gravity bends a hair of "l" = 5.