https://www.youtube.com/watch?v=hFZFjoX2cGg
The video
shows squirrels brilliantly conquering a diabolically difficult obstacle course to get at a delicious
treat. If you’re not one of those who’ve seen it (22.5 million in the first
week, late in May) don’t miss it. Around the 16 minute mark he (Mark)
demonstrates the launch platform in slow motion. It turns out that squirrels
are amazing at figuring out where and how they’ll land when flying through the
air.
Just like
cats! And Mark mentions cats’ ability to land on their feet when dropped upside
down. He also discusses briefly the physics behind this ability. Angular
momentum (or Moment of Inertia) plays a part. Cats and squirrels control their
rate of spinning by extending or pulling in their legs. Figure skaters do this
as well. Pulling your arms in makes you spin faster; extending your arms slows
your spin. Of course, figure skaters have to keep at least one foot on the ice.
Here’s an illustration of that from my book Faster,
Higher, Smarter.
Squirrels
and cats flying through the air have four appendages to use to control their
angular momentum.
But that’s
not the whole story. Figuring out how cats can turn over in a split second
to get their feet under them took scientists nearly three hundred years.
First up
was Antoine Parent, a French mathematician best known for a three volume
treatise on Analytical Geometry in 1700. He explained (incorrectly) that the upside
down cat (A below) hollows its back, moving its centre of gravity above its axis (B); this
makes it unstable, causing the cat to rotate to the feet down position (C). The
explanation doesn’t work because there’s nothing supporting either end of the
cat, so there’s nothing to make it rotate.
Many other
scientists studied the cat problem. Probably the most famous was James
Clerk Maxwell, who formulated the laws of electro-magnetism, unifying
electricity, magnetism and light. Maxwell developed a reputation while at Cambridge in
the 1830s for throwing cats out of windows. (He denied this, saying that he
only dropped cats onto a table or bed, from a height of inches). No-one came up
with any good explanations. Many suggested that the cats “cheated” by pushing
off against the hands that were dropping them. The difficulty for scientists in solving the problem was that cats right
themselves faster than the human eye can follow.
A breakthrough
came in 1894. Etienne-Jules Marey, a French scientist, made brilliant use
of the new technology of chronophotography. He took a series of pictures at 12
frames/second, of a cat turning over in the air. Marey was inspired by the work
of Edward Muybridge, who famously took a series of pictures of horses in motion,
settling an age-old debate about whether all four hooves are ever off the ground.
(They are).
The images start at the right and move to the left. |
But even
this wasn’t quite enough to solve the problem. It showed clearly enough that the cat
wasn’t pushing off against the hands dropping it. Marey gave an almost correct explanation of the cat changing its angular momentum first by pulling in its front paws and extending its back legs to give it more intertia at the back, and allowing it to turn its front half more; and
reversing the procudure to allow the back half to 'catch up'. But this still doesn't explain how the cat starts out with no angular momentum but can still rotate. There were also suggestions that the cat achieved that by rotating its tail. The tail rotation theory,
though, didn’t explain how tailless Manx cats can also fall feet down.
The
solution had to wait for NASA-funded scientists Kane and Scher. In 1969 they
published "A dynamical explanation
of the falling cat phenomenon". The key to their model is the exceptional flexibility of the cat's spine. The cat bends to approximate two cylinders (chest and lower body) at right
angles to each other. The total angular momentum of each of the “cylinders” and
the overall connected body remains zero as the cat twists around to place its
legs below it.
Why did NASA fund the study? Because it needed to develop
strategies for astronauts floating in space to orient themselves. It worked!
Thanks, kitty.
Astronaut Bruce McCandless on First-ever Untethered Spacewalk |
2 comments:
Oh wow, what a great connection between squirrels and cats -- and astronauts!
And I gotta say EEP! about the un-tethered spacewalk.
Thanks, Paula.
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