Skip to main content


Showing posts from March 30, 2017

Bullets, Bikes and Rotor Blades: Random Motion, Perfectly Predictable

Bullets rip from the barrel of modern rifles at more than 3000 feet per second.Tanks fire armor-piercing shells that travel nearly twice that speed, just over a mile a second.Rotor blades on helicopters sweep the air at a constant speed, but a small change in the pitch (tilt) of the blades causes the ‘copter to rise, drop, hover or hurtle through the air at more than 100 knots.

Each of these complex motions is almost perfectly predictable moving through an utterly random medium: air.The atmosphere, from sea level to stratosphere, is nothing but randomly moving molecules.The molecules of air are vanishingly small,so each cubic foot of air has about 30 sextillion molecules (3 with 22 zeroes) of air in it at any moment.
Since air is mostly nitrogen and oxygen, most air molecules are just under a millionth of a millimeter long. These tiny particles move in random directions: up, down, left, right and everything in between at speeds around 1000 miles per hour at room temperature and norma…