Skulls in the Stars

Updated slightly to add even more cat goodness!

The more I research, the more it becomes clear that cats caused all sorts of mischief in the scientific community in the late 1800s!  The source of this mischief is the feline ability to turn themselves over in freefall and land on their feet, even when released at rest with no rotational motion.  As I have noted in a previous post, this ability is, at a glance, seemingly at odds with the conservation of angular momentum — though in reality it is not!  In a rigid body, the angular momentum of the object is directly proportional to its rotational speed.  In a flexible body such as a cat, however, different sections can rotate in different ways, producing a net overall rotation even if the cat’s total angular momentum remains zero.

Resident feline fluidity expert Cookie demonstrates the bendy-ness of cats.

The debate, and confusion, was sparked in 1894 when Étienne-Jules Marey presented a sequence of photographs to the Paris Academy showing a cat flipping over at rest.  As was later reported in the New York Herald, Marey’s observations were met with hilarious incredulity at the meeting:

When M. Marey laid the results of his investigations before the Academy of Sciences, a lively discussion resulted. The difficulty was to explain how the cat could turn itself round without a fulcrum to assist it in the operation. One member declared that M. Marey had presented them with a scientific paradox in direct contradiction with the most elementary mechanical principles.

Fortunately for the dignity of the scientific community, researchers quickly realized that Marey was correct: non-rigid bodies can flip over, even starting from rest, while conserving angular momentum.  This led to a century-long investigation into how, exactly, a cat achieves this feat (you can read about the history in another blog post of mine).

Side view of a falling cat, by Marey. Images chronological from right to left, top to bottom.

Other researchers, however, found immediate inspiration in the cat’s newly-appreciated ability and its implications for physics.  Inspired by Marey’s work, mathematician Giuseppe Peano in fact argued that the cat’s flipping talent provided a lesson and a solution for a problem in the most unlikely of places: geophysics!

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