Projectile Motion
Forces and Motion

Falling cats

Stories from Physics for 11-14 14-16 IOP RESOURCES

A number of scientific investigations have studied the motion of falling cats. Galileo had one of the characters in his dialogue deliver this quip to attack an Aristotelian:

‘his author must believe that if a dead cat falls out of a window, a live one cannot possibly fall too, since it is not a proper thing for a corpse to share in qualities that are suitable for the living.'

Maxwell wrote in a letter during his time at Cambridge:

There is a tradition in Trinity that when I was here I discovered a method of throwing a cat so as not to light on its feet, and that I used to throw cats out of windows. I had to explain that the proper object of research was to find how quick the cat would turn round, and that the proper method was to let the cat drop on a table or bed from about two inches, and that even then the cat lights on her feet.

Some Stanford University physicists presented an analysis of the motion of falling felines based on a model of the cat as two joined cylinders. A more recent paper presents evidence from dropping a toy cat fitted with an accelerometer. The researchers argue that changes in acceleration cause a fear response in a cat and hence define a variable, the ‘coefficient of the cat’s fear’ as the derivative of acceleration during free fall. The authors present an explanation for the urban legend that cats often die when falling from a height of seven storeys but may survive falls from both greater and lesser heights. They argue that a seven-storey fall takes about two seconds, which corresponds with the upper limit of the coefficient of fear and so cats falling from relatively small heights may be unprepared to land.

A falling cat may appear to violate the principle of conservation of angular momentum, as it is seemingly able to rotate without the application of an external torque. However, it has been argued that a falling cat moves its body in such a way that the front and back halves rotate in opposite directions, resulting in a zero net change in angular momentum.


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