[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index][Subject Index][Author Index]

Re: FLUFF AND FALLING




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.