From: gbt@cray.com (Greg Titus)
Subject: Re: Acceleration, cats...
Organization: Cray Research, Inc.
Distribution: sci
Date: 23 Dec 92 14:27:45 CST

In article <Bzq6u7.6AB@news.cso.uiuc.edu> jbh55289@uxa.cso.uiuc.edu (Josh 'K' Hopkins) writes:
>pgf@srl03.cacs.usl.edu ("Phil G. Fraering") writes:
>
>>... some cats have fallen from ten or twenty stories and sometimes
>>survived ...
>
>>What I want to know is, how the ability to fall from 100-150 feet
>>up was _selected for_ by evolution. It implies that they went through
>>a period of development where cats that could do that were outcompeting
>>cats that weren't, to the extent that a large number of cats today can
>>do it.
>
>... you can't blame everything on evolution.  The
>apendix comes to mind.  Some things are around simply because they weren't
>selected against.
>
>...  The test I believe you are
>refering to was studying just why it is that "cats always land on their feet."
>If you toss one of the second story window they don't have time to twist into
>the right position.  A higher fall may sound more dangerous but it gives the
>cat time to get into landing position.  Thus it's actually safer.

Two points ...

Josh, it takes very little altitude for a cat to land on its feet.
Initially positioned with feet upward, both of mine can do it given
three feet of altitude; neither can do it given two feet or less.
(Test performed under humane conditions using a bed as a landing pad.
Both cats rewarded with sardines afterward.)

What Phil was talking about is a separate study to check into some
surprising results regarding height of fall vs. extent of damage to
cats.  This was discussed in (I think) Science News a while back.
Somebody got curious after hearing the report of the cat that fell out
of a 10th (?) story window in San Francisco during the Santa Cruz
earthquake a few years ago, and received minimal damage.

It turns out that cats have a particular muscular/skeletal arrangement
they go into when they enter free fall, which is designed to maximize
the shock absorbance of the whole cat and minimize damage to any
particular part of it.  However, this mode does not work all the way
up to feline terminal velocity, with the result that as fall height
increases past 10 or 15 feet, cats experience more and more damage
upon landing.  Above 30 or 40 feet, they are usually very badly
injured.  However, the tensed-up shock absorbing mode does not last
very long.  If no landing occurs, then the cat begins relaxing, with
the result that a cat falling from 80 to 100 feet lands as a blob, and
often has very minor injuries.

Basically, it turns out that a relaxed cat can impact at feline
terminal velocity without much damage.  The tensed mode reduces the
injury rate to zero for impact velocities below a certain value, but
adversely affects survivability between that point and somewhat less
than terminal velocity.

Although I don't recall the article mentioning it, one hypothesis to
explain this is that there is an acceleration value above which a cat
enters this "shock absorber mode".  As the cat approaches terminal
velocity in a fall the acceleration decreases, perhaps to the point
that the autonomous system that handles impact management decides that
the cat is no longer falling, and lets loose the muscular tension.

Or in other words, it's a bug masquerading as a feature.

I give away my Science News magazines, but perhaps somebody out there
has access to an index for the last couple of years, and could find
the article.

greg
-- 
--------------------------------------------------------------
Greg Titus (gbt@zia.cray.com)             Compiler Group (Ada)
Cray Research, Inc.                               Santa Fe, NM
Opinions expressed herein (such as they are) are purely my own.