Perpetuum Mobile

Read the book Does Anything Eat Wasps over the Labor Day weekend. Most of it was not stimulating. However, I did find some interesting information on cats.

I'm reminded of a study reported in the Journal of the American Veterinary Medicine Association in 1987 by WO Whitney and CJ Mehlhaff, two New York vets, entitled 'High-rise Syndrome in Cats'. The study was also summarised in Nature a year later. Briefly, the authors examined injuries and mortality rates in cats that had been brought to their hospital following falls ranging from between two and 32 storeys. Overall mortality rates were low, with 90 per cent of the cats surviving, a fact that supports the correspondent's ailurophobic friend. However, the study unexpectedly found that the incidence of injuries and death peaked for falls of around seven storeys, and then actually decreased for falls from greater heights.

A falling cat has a higher surface area to mass ratio than a falling human, and so reaches a terminal velocity of about 100km per hour (about half that of humans). They are also able to twist themselves so that the impact is spread over four feet, rather than our two. And, as they are more flexible than humans, they can land with flexed limbs and dissipate the impact forces through soft tissue. To answer the paradoxical increase in survival rates once seven storeys has been reached, the authors suggested that an accelerating cat tends to stiffen up, reducing its ability to absorb the impact. However, once terminal velocity is reached, there is no longer any net force acting on the cat, and so it will relax, increasing both its flexibility and the cross-sectional area over which the impact is dissipated once the cat hits the ground.

When a cat is dropped, it always lands on its feet, and when toast is dropped, it always lands buttered side down. Therefore, if a slice of toast is strapped to a cat's back, buttered side up, and the animal is then dropped, the two opposing forces will cause it to hover, spinning inches above the ground.