Brian Davis wrote:
> This came up in a different newsgroup, and upon trying to answer it I
> blew it badly. I’m not sure the original group really cares, but folks
> here might, and it’s kind of interesting to me, so…
>
> Let’s say you have a person (named, let’s say, “Callie”) standing in
> the middle of a large airlock (10 [m] long by 3[m] by 3[m]). The bad
> girl opens the large doors at the end, “blowing the lock” (it starts
> at 1 [Atm]). What happens to the helpless heroine? I understand
> decompression, but I’m trying to figure out how fast (if at all) they
> “exit” the airlock. For a first cut, I assumed the doors instantly
> crack open 10 [cm] along their entire 3 [m] length, forming a “breach”
> with an area of 0.3 [m^2] through which the air starts rushing at
> roughly Mach 1 (I know it would be less, but ballpark). Back by
> Callie, the cross-sectional area is about 9 [m^2], so conservation of
> mass (assuming uniform density) says the airspeed by her is a gusty
> 11.1 [m/s]… which is pretty much trivial. I assumed she is accelerated
> “breachward” by the stagnation pressure of this flow against the front
> of her body (frontal surface area 0.36 [m^2, mass of 45 [kg]), but the
> result is a really trivial acceleration. Running it through Excel (to
> keep track of the rapid density/pressure drop, which reduces the
> stagnation pressure all the more), I get her hitting the breach after
> a little over 8.5 [sec], and the leisurely pace of about 0.67 [m/s] (a
> slow walk). She really only accelerates for the first couple seconds,
> after that the lock is at such a low pressure that the remaining
> “wind” just doesn’t have enough force to do anything.
>
> OK, so what did I screw up?
Nothing, I'd say. The ability for explosive decompression to push
people around is usually exaggerated. Your results sound qualitatively
like I'd expect -- it'd budge her a little at first but very rapidly the
ambient air pressure would drop to the point that it wouldn't have much
of an effect.
--
Erik Max Francis && max@[EMAIL PROTECTED]
&& http://www.alcyone.com/max/
San Jose, CA, USA && 37 18 N 121 57 W && AIM, Y!M erikmaxfrancis
Because a bullet has no name / And sees no face
-- Skee-Lo
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