Re: buoyant cannon balls, was Parents' day Gem

[LUDWIK KOWALSKI <KOWALSKIL@alpha.montclair.edu>]

> Date: Thu, 30 Oct 1997 22:44:33 -0600
> From: brian whatcott <inet@intellisys.net>
> Subject: Re: Buoyant Bullets
>
>    It is a common-place of ballistics that a well-spun shell by holding 
>    its attitude near to its initial elevation develops lift as it drops.
>
>    It is also well known that the general run of say - pistol bullets nutate
>    markedly about their flight axis and do not develop lift in the same way.

Would you expect the same thing to happen for a non-spinning cannon ball, a
spherical shape projectile?

>    John did NOT report lift due to a horizontal drag force (or if he did,
>    he doubtless regrets it.) I recall he mentioned there must be at least a 
>    small vertical component.

You are right that "a small vertical component" of v is probably essential 
here. If this is true then a horizontally fired ball must have "initial 
lift" equal to zero at any initial velocity. And the lift must increase
in time, at least for a while. Is Leigh right that the quadratic F(v)
dependence is not essential and that the same may be expected from the
F=k*v? 

I wish I had time to play with Interactive Physics now, or to explore 
textbooks on ballistics. Keep in mind that the third dimension, in the 
virtual world of IP, is absent. How should "a-virtual-in-a-virtual" be
called? Super-virtual or non-real? IP is certainly not the best tool for
dealing with air rersistance.
                                                      ludwik kowalski