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Date: Mon, 22 Aug 2005 21:38:57 -0600 (MDT)
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To: julian@elischer.org
From: "M. Warner Losh" <imp@bsdimp.com>
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Cc: freebsd-hackers@freebsd.org, sos@freebsd.org, borjamar@sarenet.es
Subject: Re: IBM Active Protection System Approach
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In message: <430A8E2B.6040408@elischer.org>
            Julian Elischer <julian@elischer.org> writes:
: You have about 1/4 a second to get the heads in once you detect that
: you are falling.

Yes.  For a 4' fall, we know it takes 1/2 a second to reach the
ground:
	s = 1/2 a t^2 + v0 t + s0

s0 = 0, a = 32 f/s^2, v0 = 0, s = 4, solve for t gives 1/2 a second to
make the fall.  Sos was saying 10's of ms to retract the heads, so
even a 300ms response time wouldn't be fatal, but it would be pushing
the limits.

For a 2' fall, you have even less time.  More like 350ms.  1' is 250ms...

Warner