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*To*: Multiple recipients of list <dinosaur@lepomis.psych.upenn.edu>*Subject*: Re: FLUFF AND FALLING*From*: "Nicholas R. Longrich" <longrich@phoenix.Princeton.EDU>*Date*: Sat, 9 Dec 1995 13:07:11 -0500*Reply-to*: longrich@phoenix.Princeton.EDU*Sender*: dinosaur@lepomis.psych.upenn.edu

On Sat, 9 Dec 1995, Rob Meyerson wrote: > >I'd have to agree with you about the cushioning theory, at least as the= > sole=20 > >mechanism for their survival, if it does indeed help at all. I think that= > =20 > >while the fluffy cushion idea has SOME merit, I think perhaps an=20 > >even=20 > >larger consideration has to be given to how the down would affect the=20 > >drag coefficient of the little critter. Put mo simply, aren't you just=20 > >as likely to get saved by drag from the down slowing your fall as you are= > =20 > >from it cushioning it? > > Perhaps, but wouldn't the effect of drag be greater on a larger animal than= > on a smaller? It's like the amount of force required to move a dolphin is= > smaller than the amount needed to move a sperm whale (ignoring inertia for= > the moment), because the latter has a much larger body. The absolute amount of drag is greater, the relative amount is smaller. Take a fish, for example. Double its length. Surface area increases as the square- that is, a fish twice as long has 4x the surface area. Volume, on the other hand, increases as the cube- volume will increase 8x. So the proportional surface area- surface area divided by volume- is exactly one half as much in the big fish as in the smaller fish, so the relative amount of drag is less. Big things have proportionately less surface area. This is why polar bears get so big, so that they lose less heat. It also explains how those supertankers can go so damn fast- something like 25 or 30 knots. It also explains why there is a maximum size on how big a flying animal can get, because downward pull relates to your mass(which is related to your volume) and upward lift is related to your surface area. Mass increases much more quickly than surface area, so bigger animals have more trouble staying aloft. So a small animal has a lot more drag per pound of body weight than a big one. -nick L.

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