Momentum and kinetic energy of a glacier

A cubic-kilometer glacier would have a mass of about 10¹² kg. If it moves at a speed of 10^-5 m/s, then its momentum is 10⁷ kg·m/s. This is the kind of heroic-scale result we expect, perhaps the equivalent of the space shuttle taking off, or all the cars in LA driving in the same direction at freeway speed. Its kinetic energy, however, is only 50 J, the equivalent of the calories contained in a poppy seed or the energy in a drop of gasoline too small to be seen without a microscope. The surprisingly small kinetic energy is because kinetic energy is proportional to the square of the velocity, and the square of a small number is an even smaller number.

A massive glacier tongue flows down the Argentière Valley. Photo: (c) 2004 D.Bolius, www.photoglobe.info