Cats are tree climbers by nature. To protect themselves from potentially dangerous falls, they evolved with flexible bodies and an incredible sense of balance in their inner ear which gives them the ability to land on their feet.
In fact, the reason people say cats have 9 lives has a lot to do with the fact that many cats have been known to fall from incredible heights and somehow survive scot-free. But, do cats actually always land on their feet? What determines whether they do?
The physics of why cats always land on their feet
Assuming they have enough time to turn around during their fall, healthy, able-bodied cats will probably land on their feet, even if they fall backwards. This ability is known as the ‘righting reflex’. It’s an innate ability in cats, which starts to develop at 3-4 weeks of age and is perfected at 6-9 weeks.
Cats have a vestibular apparatus in their inner ear which acts as a balance and orientation compass. It’s what enables them to stand steady, even on small surfaces, or to make incredible jumps! It is also this highly developed inner ear that enables cats to always know which way is up. If they’re falling backwards, their inner ear immediately tells their brain they must turn around before they hit the ground.
It helps that cats have extremely flexible spines: They have long tails, no collarbone and their backbone consists of 30 vertebrae (compared to 24 for humans). This enables them to bend their bodies easily, and twist it in the direction of the ground before they hit it.
Much like a flying squirrel, a cat spreads out its body as it flies through the air to increase drag and slow their fall. Once they approach the ground, they position their legs underneath their bodies so that the impact will distribute evenly throughout. Their powerful legs and joints act as shock absorbers when they land.
Does it hurt when cats land on their feet?
Though their righting reflex enables them to land on their feet, cats aren’t necessarily safe from injury when they fall. A study performed in 1987 by the New York Animal Medical Centre showed that 10% of cats who fell from tall buildings died as a result of the fall, and 37% of those who survived required emergency care. Common injuries following a fall include internal lung injuries, broken bones or fractures, and traumatic brain injuries.
The survival rate depends largely on the height from which cats fall. Despite their low body-volume-to-weight ratio which slows their speed, they need enough time to stretch out their bodies while they fall. This increases drag and further decreases how fast they hit the ground (their terminal velocity is around 60 mph while it's 120 mph for humans). Additionally, cats need enough time to be able to twist their bodies and position it in a way that prepares them for the impact of landing.
In this sense, cats who fall from higher up are actually less likely to suffer serious injuries. Indeed, in the same 1987 study, cats who fell from 7-32 stories suffered less injuries than those who fell from 2-6.
However, nothing guarantees your cat won’t get hurt from sustaining a fall. Overweight cats and senior cats, for example, are much less likely to be able to right themselves before they land. If you live in an apartment building and have a balcony, make sure you install a net or build a catio to keep your cat safe. In a house, don’t leave windows open on the upper floors. Better to be safe than sorry!