THE FLIPPING CAT AND THE SPINNING EARTH
A cat released with his feet pointing up needs only a fraction of a second to point his feet down. How does he do it, with nothing to push off of?1 Some people say that the cat does it by spinning the tail. On closer inspection this turns out to be false. As an experimental fact, tailless cats are just as good as the tailed ones in flipping over. Alternatively, a theoretical argument shows that to accomplish a 180° flip in a fraction of a second, the cat would have to spin its tail so fast that its tip would have to break the sound barrier, or to come close. This would create a sonic boom, or a loud whistling at the very least. And the enormous centrifugal force would cause a part of the tail to tear off and become a deadly projectile, almost like a bullet. So the [tail] theory quickly flunks the sanity test.
What makes the cat's achievement surprising is that his spin, having started at zero, must remain zero, given that no
1 It is not hard to do a similar experiment on oneself, by sitting in a swivel chair and trying to turn around without touching the ground.