Terminal velocity of an Etruscan shrew

August 25, 2016 6:12 PM

Smaller, lighter animals can fall from further up without being harmed (I believe). Is there a mammal that is so small it could fall from any height and not be hurt? Is my basic premise wrong? Does terminal velocity figure into the explanation?
posted by Naib to Science & Nature (6 answers total)

Not a mammal, but I know ants can't be hurt by being dropped. They hit terminal velocity after just a few inches. They tested it on a Japanese quiz show awhile back by dropping one from the top of a giant stadium. It was the dumbest yet best thing I ever saw on that show.
posted by Caravantea at 6:19 PM on August 25, 2016 [11 favorites]

This paper claims a mouse will survive a 1000' drop, though without any actual data, of course. I'm sure a mouse will reach terminal velocity before it falls 1000'. The paper explains why this is (terminal velocity is indeed the answer).
posted by ssg at 6:24 PM on August 25, 2016 [1 favorite]

Best answer: Some general reading on the subject:
On Being the Right Size by J. B. S. Haldane
On Growth and Form by D'Arcy Wentworth Thompson
posted by j.edwards at 7:00 PM on August 25, 2016 [4 favorites]

Some of the can't-be-hurt aspect is, I think, a consequence of the square-cube law. The cross-sectional area of organs (especially bones), dictates how widely force can be diffused, while the mass (which is roughly proportional to volume) dictates the actual energy to be dissipated on impact, so the higher the volume-to-area ratio, the more traumatic a fall will be. Smaller animals have smaller ratios.

Smaller creatures also typically have lower terminal velocities, I think, for reasons which are a bit more aerodynamically complicated. Both factors suggest very small creatures would be very good at not dying from falling. Not being hurt at all seems unlikely for a mammal, but I can well believe they could survive, possibly without very serious injury.
posted by jackbishop at 7:40 PM on August 25, 2016 [1 favorite]

Best answer: The famous quote from Haldane's essay is worth including here, "To the mouse and any smaller animal it (gravity) presents practically no dangers. You can drop a mouse down a thousand-yard mine shaft; and, on arriving at the bottom, it gets a slight shock and walks away, provided that the ground is fairly soft. A rat is killed, a man is broken, a horse splashes. For the resistance presented to movement by the air is proportional to the surface of the moving object. Divide an animal’s length, breadth, and height each by ten; its weight is reduced to a thousandth, but its surface only to a hundredth. So the resistance to falling in the case of the small animal is relatively ten times greater than the driving force."
posted by crocomancer at 2:02 AM on August 26, 2016 [3 favorites]

Cats are pretty good at falling from heights. In one study*, 90% survived falls of up to 32 stories, average fall 5.5 stories. However, many of the survivors had recoverable injuries.

*Study was of cats who fell accidentally from tall buildings, not deliberately dropped.
posted by beagle at 2:45 AM on August 26, 2016 [2 favorites]