Automatics

[Tim May]

("Automatic's" in thread name changed to "Automatics" for obvious reasons.)

At 7:33 PM -0700 6/10/01, David Honig wrote:
>At 05:11 PM 6/10/01 -0700, petro wrote:
>>
>>	Secondly, if you think *ANY* firearm you can fire standing up
>>will "Knock them on their behind", take a high school physics class.
>>
>
>Well said, but:
>In _The Irish War_ there's a description of IRA improvised recoilless
>'rifles' which, like their .mil-industrial analogues, toss an equal
>mass out the back end.  The reacting countermass is a bunch of flakes
>which dissipate the KE against the atmosphere.
>
>[Ie, consider a barrel open at both ends.  Put missile, charge, countermass
>flakes in that order.  Point missile at thing you don't like, and keep
>friendlies a few meters away from the countermass ejection end of the barrel.]
>
>........
>
>That said, an (e.g.) hip or knee shot on a biped will cause it to fall
>approximately
>back if the posture is right.  That also is just the physics of actively
>balanced inverted pendula, biomechanics.

Speaking of physics, your physics is out of whack.

For the recoilless rifle described above, there is no need to 
"dissipate the KE" of the flakes or anything else! Once the flakes 
(or whatever) are propelled backward, it doesn't matter whether they 
flutter in the wind or fly to China. (This is all very similar to the 
common misconception that rockets "push" on the atmosphere as they 
expel exhaust particles. They don't.)

And KE (kinetic energy, for anyone just joining in and wondering) is 
not what matters for recoil calculations. Momentum, MV, is what 
matters.

How this Irish makeshift recoilless rifle actually works is unknown 
to me, but the dissipation of KE by the chaff is not germane. The 
expulsions of some mass (M) at some velocity (V) is germane, as 
above, but not the way the mass behaves once it has been propelled 
backward.

--Tim May




-- 
Timothy C. May         tcmay at got.net        Corralitos, California
Political: Co-founder Cypherpunks/crypto anarchy/Cyphernomicon
Technical: physics/soft errors/Smalltalk/Squeak/agents/games/Go
Personal: b.1951/UCSB/Intel '74-'86/retired/investor/motorcycles/guns