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