
2-Stage Light Gas Gun - luu
http://www.chrisfenton.com/2-stage-light-gas-gun/
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pstuart
The money quote:

My Mom actually made me collect all of the pieces, lay them out, and try to
root-cause the failure.

~~~
andrewflnr
The part that made me laugh out loud was "Whatever happened to just grounding
someone?" right after that.

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tlarkworthy
Might have been wiser to use helium instead of hydrogen. Great experiment,
would have liked to have seen a video though

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ChuckMcM
Much more fun than shooting tennis balls out of tin cans taped together. There
is a bit of a problem with the description however which is that while air
speed will be limited to the mach number that is the _net_ air speed.
Generally in a projectile weapon the accelerating gas is moving along with the
projectile and so within the moving gas cloud the projectile can much much
faster than the surrounding air. That is why your typical 30-30 hunting rifle
will have a muzzle velocity >2000 fps which is in excess of the mach number
(and the speed of sound).

~~~
mechagodzilla
But you're limited by the mach speed of the fluid pushing the object, not the
mach speed of the fluid you're _traveling_ through. A bullet out of a rifle is
limited by the mach speed of the hot gases created during combustion. A
compressed-air gun, however, is limited to the speed of sound in compressed
air.

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WhiteNoiz3
This is a rediculously unsafe project. Plastic PVC is not rated to be able to
contain that much pressure (better to have used metal pipe and brass hardware)
and hydrogen gas is extremely flammable.

~~~
bradleyland
PVC also doesn't show up well on x-rays either. A student at our high school
had a potato cannon explode next to his hip one year. He ended up with a trip
to the emergency room where the radiology tech shared that nugget of wisdom
with him. Fortunately, when PVC fractures, most of the pieces remain large, so
he was mostly bruised, but he had a couple of nasty cuts.

In this case, however:

> Fortunately, everyone was safely behind a barrier a safe distance away, and
> no one was hurt.

It sounds like this particular experiment was conducted by people with enough
sense to stay out of harms way.

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SchizoDuckie
Great experiment, great writeup, great parenthood. Extrapluskudo's to your mom
for making you figure out what went wrong. That's the way to teach something.
Build->Fail->Rinse->Repeat

