Newsgroups: comp.robotics
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From: ajackson@ernie.Princeton.EDU (Andrew William Jackson)
Subject: Re: Measuring the acceleration of an arrow.
Message-ID: <1992Dec1.024656.4128@Princeton.EDU>
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References: <1992Nov23.201213.1@ulkyvx.louisville.edu> <1992Nov24.183136.16334@fid.morgan.com> <BENEDICT.92Nov30163019@chaos.utexas.edu>
Date: Tue, 1 Dec 1992 02:46:56 GMT
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someone suggested using an interferometer to measure the speed of a 
bullet with a little reflector on it.

Tom Benedict writes:

> "My current idea is to have a specially made bullet with a small
>reflector on the end.  The gun is anchored and aimed at a small hole
>in a metal plate about 100 feet away.  Through this hole is aimed a
>laser, which through interferometry should be able to measure the
>speed of the bullet at any moment in time.  The distance of 100 feet
>or so should insure that the bullet has enough drop so that it doesn't
>go through the hole and shoot the interferometer (a nastily expensive
>piece of equipment).  Problems:  It's expensive, I don't know if an
>interferometer can measure supersonic speeds like that, and it ain't
>easy to set up.  Any ideas?"


If a bullet goes 500 m/s (is this a good approx?) and if the wavelength
of light is 5000 ang. each 1250 ang will correspond to one fringe thus
requiring a photo detector capable of sensing a 4 gHz signal!

Also as far as the breach pressure there is no reason I see why you can't
make a 1000 atm. pressure sensor.

ajackson@ernie.princeton.edu

