Clarification of physics of recoilless rifle

[David Honig]

At 12:46 AM 6/11/01 -0700, Tim May wrote:
>
>At 7:33 PM -0700 6/10/01, David Honig wrote:
>>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.


>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! 

My physics is fine.  I assume the reader can tell that I'm 
explaining the reason for using *individually lightweight flakes* 
separately from the trivial symmetric-reaction-mass part of the rifle.

After all, a reader would be asking themselves, why not just use
a slug of the same mass, or even some ball bearings (shot), since he 
indicates (by saying "equal mass") that this would work?

And I explain the safe dissipation of the flakes' *energy*, not momentum 
(which as you point out is what matters for the recoilless-ness) 
because the flakes dissipate their motion as *heat* via  
viscous drag through the atmosphere.  



>How this Irish makeshift recoilless rifle actually works is unknown 
>to me, but the dissipation of KE by the chaff is not germane. 

Picture yourself using one in cramped quarters.  The chaff 'flying off to
China'
is a practical concern.

Or read the book.  Plus, you can learn how to turn common household objects
into mortars.

dh