Cat righting reflex

File:Falling cat 1894.jpg

Images of a falling cat which appeared in the journal Nature in 1894, captured in a chronophotography by Étienne-Jules Marey.

The cat righting reflex is a cat's innate ability to orient itself as it falls in order to land on its feet. The righting reflex begins to appear at 3–4 weeks of age, and is perfected at 6–7 weeks. Cats are able to do this because they have an unusually flexible backbone and no functional clavicle (collarbone). The minimum height required for this to occur in most cats (safely) would be around 30 centimetres (12 in). Cats without a tail also have this ability, since a cat mostly moves its hind legs and relies on conservation of angular momentum to set up for landing, and the tail is in fact little used for this feat.

Technique

Schematic animation of the motion involved

File:BIOASTRONAUTICS RESEARCH Gov.archives.arc.68700.ogv

Cats falling at normal gravity and with no gravity

After determining down from up visually or with their vestibular apparatus (in the inner ear), cats manage to twist themselves to face downward without ever changing their net angular momentum. They are able to accomplish this with these key steps:

1. Bend in the middle so that the front half of their body rotates about a different axis from the rear half.
2. Tuck their front legs in to reduce the moment of inertia of the front half of their body and extend their rear legs to increase the moment of inertia of the rear half of their body so that they can rotate their front further (as much as 90°) while the rear half rotates in the opposite direction less (as little as 10°).
3. Extend their front legs and tuck their rear legs so that they can rotate their rear half further while their front half rotates in the opposite direction less.

Depending on the cat's flexibility and initial angular momentum, if any, the cat may need to perform steps two and three repeatedly in order to complete a full 180° rotation.

Terminal velocity

In addition to the righting reflex cats have a number of other features that will reduce damage from a fall. Their small size, light bone structure, and thick fur decrease their terminal velocity. Furthermore, once righted they may also spread out their body to increase drag and slow the fall to some extent. A falling cat's terminal velocity is 100 km/h (60 mph) whereas that of a falling man in a "free fall position" is 210 km/h (130 mph). At terminal velocity they also relax as they fall, which protects them to some extent on impact. However, it has been argued that, after having reached terminal velocity, cats would orient their limbs horizontally such that their body hits the ground first.

Injury

With their righting reflex, cats often land uninjured. However, this is not always the case, since cats can still break bones or die from extreme falls. In a 1987 study, published in the Journal of the American Veterinary Medical Association, of 132 cats that were brought into the New York Animal Medical Center after having fallen from buildings, it was found that the injuries per cat increased depending on the height fallen up to seven stories, but decreased above seven stories. The study authors speculated that after falling five stories the cats reached terminal velocity and thereafter relaxed and spread their bodies to increase drag. However, critics of the study pointed out a sampling error in that instantly fatal falls were not included (as an already dead cat would not be taken to the vet), questioning the authors' conclusion that the injury rate declined for higher falls.

See also

• Buttered cat paradox
• Falling cat problem – The mathematical problem of explaining the physics of the cat righting reflex
• High-rise syndrome

External links

• Why cats land on their feet
• National Geographic video on the cat righting reflex
• The miracle of the falling cat