Cats have amazing control over their bodies. If you hold a cat upside down a mod

Question

Cats have amazing control over their bodies. If you hold a cat upside down a moderate height off the floor and drop it, it manages to right itself in midair and land on its feet. Isn’t this a violation of the conservation of angular momentum? After all, the cat starts upside down, and then it somehow rotates until it is right-side up. Which of the following is the most plausible explanation for this phenomenon? Select one: a. The observation that 'cats always land on their feet' is based on an optical illusion. Cats dropped from an upside-down position cannot possibly land right-side up because of the conservation of angular momentum. b. By shifting the location of its center of mass, a cat can cause gravity to exert a net torque on it, causing its body to twist in a certain direction. c. By manipulating its body, a cat can control the moment of inertia of different parts of its body in such a way that it can reorient itself in midair despite the fact that its angular momentum is zero the whole time. d. When a cat falls, it actually is in contact with something: the air. Frictional forces between air and the cat’s body are small, but they can exert enough torque to rotate the cat 180°.

Explanation / Answer

The answer is (c).

The cat can control the moment of inertia of different parts of its body and reorient itself such that the angular momentum is zero. The cat first tucks its front legs such that the moment of inertia of the front part reduces and extends its rear legs such that the moment of inertia of the rear half of the body increases. So the front part of the rotates by a large amount while the rear part rotates by a small amount but in opposite direction thus conserving the angular momentum. It then extends the rear legs and tucks the front legs and rotates the rear part more. Thus it can rotate its entire body while conserving the angular momentum.

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