Sunday, September 26, 2010

Falling Cats

Cats like high places, and they often fall. Clinics often see cats injured in falls, but they survive falls that would splat people into ketchup.  A good post on falling cats is from Don Burleson, and another is Wikipedia.

A cat falls more slowly than person does, because of its fluffy fur catches the air and light bone structure. Cats have a terminal velocity of 60 mph where as a person falls at over twice that or 130 mph. (Actually ski divers fall more slowly facedown with arms extended, and about 200 mph in a vertical diving position.) Remember that kinetic energy is proportional to the square of the velocity, so the potential damage on hitting the ground is over four times greater for a human than for a cat (on a per pound basis).

Of course cats, orient themselves to land on their feet, as shown at right these cool photos from Berkeley.   The physics of the cat turning involve extending its legs to change it moment of inertia.

  1. Bend in the middle so that the front half of their body rotates about a different axis than the rear half.
  2. Tuck their front legs in to reduce the moment of inertia of the front half of their body and extend their rear legs to increase the moment of inertia of the rear half of their body so that they can rotate their front half quite far (as much as 90°) while the rear half rotates in the opposite direction quite a bit less (as little as 10°).
  3. Extend their front legs and tuck their rear legs so that they can rotate their rear half quite far while their front half rotates in the opposite direction quite a bit less.
  4. Repeat if necessary.
The ability to live though a fall like this certainly gives an advantage to the cat evolutionally. I wonder how this reflex is encoded genetically.