The Mares Tail

That is not a feather cloud, it’s a mare’s tail and I ought to know as I carefully lifted many horses’ tails and I wondered what purpose they served.  I noticed that when it was swung around, it would deter flies from biting its ass and this was their defense in their war against insects.  This is a part of the horse that must be respected, as a tail can be used like a whip and it is a formidable weapon, especially when it is frantically swished and swayed around.  Animals’ butts may seem mundane to most people, but only creatures with an anus are able to physically segregate the acts of eating and defecating, so they don’t have to finish processing one meal before ingesting another, allowing their bodies to harvest more energy, so they can grow bigger.  People may joke and say that a moron or an unlikable person is a horse’s ass, but a horse’s tail can reveal a lot about the horse, as when it is moving the horse is thought to be frisky and energetic.

In 1581, when Galileo was studding motion, he was fascinated the regular movement of a pendulum.  A horse’s tail swings like a pendulum, but unlike the pendulum, which exhibits a periodic motion about its mean position, it does not swing at natural frequency.  Galileo discovered that for small amplitudes, the period and frequency are unaffected by the amplitude.  This breakthrough came while he sat bored during a church service in Pisa.  The chandelier overhead would swing gently back and forth, but it seemed to move more quickly when it was swinging widely (after a gust of wind, for example) and more slowly when it wasn’t moving as far.  Intrigued, Galileo decided to measure how much time it took for each swing, using the only approximately periodic event to which he had ready access.  Since clocks with second hands didn’t become common until the 18th century, Galileo used the beating of his own pulse.  He found the number of heartbeats between swings of the chandelier was roughly the same, regardless of whether the swings were wide or narrow.  Thus, the size of the oscillations pertaining to how far the pendulum swung back and forth, didn’t affect the frequency of those oscillations.

The discovery of this natural frequency is what made the pendulum an extremely reliable source for telling time.  It is also this natural frequency, this motion at resonance, that allows a grandfather clock to use so little energy.  A single winding keeps a clock running for days.  Since animals are swinging their tails nearly all the time that they are awake, one would expect that they would want to swing them at their natural frequency to save energy.  Shockingly, horses swing their tails once per second, which is three times faster than the expected natural frequencies based on their tail length.  By swinging their tail three times faster than their natural frequency, they expend 27 times more energy than necessary, but this allows them to shoo away many more flies.

Written for KL Caley’s Thursday Write Photo – Feather Cloud.