Perhaps more intriguing than purring is the cat's ability to survive falls. The research of veterinarians Wayne Whitney and Cheryl Mehlhaff at the Animal Medical Center in New York City shed light on this ability in 1987. The cat's habit of falling out of open windows provided the researchers with an opportunity to study 115 cats that had fallen from high-rise apartments in New York City. The average fall was 5.5 stories. Of the 115 cats studied, 90 per cent survived, including one cat that fell 32 stories onto a sidewalk and suffered only a mild chest injury and a chipped tooth. Interestingly, cats that fell from 9 or more stories suffered fewer injuries than those falling from lower heights. Among cats that fell from 9 to 32 stories, only 5 per cent suffered fatal injuries, but 10 per cent of those that fell from 7 or fewer stories died.

How do cats manage to take falling so easily? For one thing, in comparison to human beings, a cat is much smaller and lighter. Also, a cat has more body surface area in proportion to its weight than a human being has. This increase in surface area results in greater air resistance, which slows the fall. The important thing, however, is that a falling cat apparently positions itself to form a sort of parachute. Less than one second after it starts to fall, a cat quickly rights itself in midair with all four legs pointing downward. The cat's inner ears act like an internal gyroscope, telling the cat which direction it is falling. With the legs pointed downward, the cat then spreads its legs so that its body forms a sort of parachute that increases air resistance. With its limbs flexed, the cat also cushions the force of impact by landing on all four legs. The force of the impact is distributed through the muscles and joints.

Whitney and Mehlhaff believe that the parachute effect comes into play mainly above four stories, at the point where the cat has reached its greatest rate of descent. Of the 115 cats the researchers studied, only 1 of 13 cats that fell nine or more stories sustained a bone fracture, whereas most of the cats that fell from lower stories suffered some type of broken bone.

source: http://animals.howstuffworks.com/pets/domestic-cat-info5.htm