Saturday, March 20, 2010

Why Cats Have Nine Lives

    Although the origin of the phrase, “cats have nine lives,” is unclear, it may be related to the fact that some cultures consider 9 a lucky number and the unusually high survival ability of cats. With their keen sense of balance and sharp hearing ability, cats are able to avoid many accidents and keep their life.
    In particular, cats are able to survive falls from very high distances—even from up to 32 stories! This can be explained by Physics. First, cats weigh only about ten pounds, so the force of the impact when they hit the ground is more than a dozen times less than that of the average person. Second, when cats fall, they spin their bodies in order to land all four feet (this is called the righting reflex). Because of this, the force of the impact is distributed across all of the cats' legs (see Fig. 1). Third, when cats land, they increase the time of landing impact by bending their feet, which allows the force of the impact to distribute across their leg muscles slowly which further reduces the pressure on the body. Finally, before landing, cats position their body such that the speed at which they are falling is reduced (due to air resistance), which further decreases the impact. In fact, the terminal velocity (the maximum velocity) with which a cat falls down is 60 miles per hour, which is about half of the terminal velocity of a human.
    A study was actually done to test the survival rate of falling cats. Conducted by veterinarians at the Animal Medical Center in Manhattan, this study examined reports of 115 cats which fell from different stories of height (Whitney & Melhaff). What this study found was that cats that fell from heights of 2 to 32 stories died only about about one out of nine times (although many suffered serious injuries). Another study done by veterinarian faculty members of the University of Zagreb reported a survival rate of 96.5% (Vnuk et al.).    Interestingly enough, the above experiments relate with a cat having nine lives: out of every nine cats falling from 32 stories (a usually fatal maneuver for humans), only about one loses its last life.
Figure 1: Falling cat. Source: http://www.ocf.berkeley.edu/~barneye/kitty.html


Reading sources:
http://www.coolquiz.com/trivia/explain/docs/cats2.asp
http://www.moggies.co.uk/html/9_lives.html
http://www.scribd.com/doc/85/Falling-Cats

Journal articles:
Whitney & Melhaff: http://www.ncbi.nlm.nih.gov/pubmed/15363762
Vnuk et al.: http://www.ncbi.nlm.nih.gov/sites/entrez

Uploaded on 12/24/2012 (originally written on 3/20/2010)

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