How do cats survive falls from great heights?

Cats' remarkable ability to survive falls from great heights is a simple and predictable matter of physics, evolutionary biology, and physiology, veterinarians and biologists say "We do know that animals exhibit this behaviour," says Jake Socha, a biomechanist at Virginia Tech university.

In the study, 132 cats brought to a New York City emergency veterinary clinic after falls from high-rise buildings, 90% of treated cats survived and only 37% needed emergency treatment to keep them alive. One that fell 32 stories onto concrete suffered only a chipped tooth and a collapsed lung and was released after 48 hours.

From the moment they're in the air to the instant after they hit the ground, cats' bodies are built to survive high falls, scientists say.

Pressure: They have a relatively large surface area in proportion to their weight, thus reducing the force at which they hit the pavement.

Terminal Velocity:  Cats reach terminal velocity, the speed at which the downward tug of gravity is matched by the upward push of wind resistance, at a slow speed compared to large animals like humans and horses.

For instance, an average-sized cat with its limbs extended achieves a terminal velocity of about 60mph (97km/h), while an average-sized man reaches a terminal velocity of about 120mph (193km/h), according to the 1987 study by veterinarians Wayne Whitney and Cheryl Mehlhaff.

Cats can also spread their legs out to create a sort of parachute effect, says Andrew Biewener, a professor of organismal and evolutionary biology at Harvard University, although it is unclear how much this slows the rate of descent.

"They splay out their legs, which is going to expand their surface area of the body, and that increases the drag resistance," he says.

Balancing centre of gravity: Through natural selection, cats have developed a keen instinct for sensing which way is down, analogous to the mechanism humans use for balance, biologists say.

Then - if given enough time - they are able to twist their bodies like a gymnast, astronaut or skydiver and spin their tails in order to position their feet under their bodies and land on them.

Shock Absorbing:  When they do land, cats' muscular legs - made for climbing trees - act as shock absorbers. "Cats have long, compliant legs," says Jim Usherwood of the structure and motion lab at the Royal Veterinary College. "They've got decent muscles. In that they're able to jump quite well, the same muscles divert energy into decelerating rather than breaking bones."

The springy legs increase the distance over which the force of the collision with the ground dissipates, says Dr Biewener.

"The impact forces are much higher in stiff collisions," he says. "If they can increase the collision time over a longer period, that reduces the impact force."

And a cat's legs are angled under the body rather than extended downward, like human or horse legs.

"You're not transmitting the forces really directly," says Dr Socha.

"If the cat were to land with its legs directly under him in a column and hold him stiff, those bones would all break. But they go off to the side and the joints then bend, and you're now taking that energy and putting it into the joints and you're getting less of a force at the bone itself."