Re: Buoyant Bullets

[Hugh Haskell <hhaskell@mindspring.com>]

> At 17:00 10/30/97 -0800, you wrote:
> > At 5:12 PM -0800 10/30/97, brian whatcott wrote:
> >
> > > Ludwik seems readily amazed today - so let me do my little to help.
> > > How about a retarding force formula *greater* than the bullet's weight.
> > >
> > > Gee whizz! That means that a bullet fired straight down at mach 2
> > > would DECELERATE!
> >
> > I'd be willing to bet it would. Is that a surprising result? I'd be
> > shocked to find any real retarding force at one atmosphere pressure
> > that would *not* decelerate a bullet fired downward at mach 2.
> >
> > Leigh
> Then I would suggest you are not a lost cause;
> where there's a component of downward velocity
> for a speeding object in air, you see that there is an upwardly
> directed component of drag - let's call it lift (?)
>
> :-)
> Brian
> brian whatcott <inet@intellisys.net>
> Altus OK

OK, I'm beginning to catch on. But to call an upwardly directed component
of drag "lift" is a bit of a stretch. Lift is not generally considered to
be "vertical", but perpendicular to the chord of the airfoil, or generally
perpendicular to the direction of motion. So when we talk about wings, the
"lift" can be in any direction (including down), depending on the
orientation of the wing. So just because the drag force is upward in the
downward fired bullet case, doesn't make it lift. Strictly speaking, any
lift generated in this case would be horizontal.

But it seems to me that all of this is missing John's point, which is that
the large drag force on the horizontally fired bullet, once the bullet has
a downwardly directed component of velocity, create a much larger vertical
component of drag than would be expected if the upward component of drag
were simply due to the downward component of velocity, thus causing the
speeding bullet to fall slower than its vertically falling counterpart.
This force is neither lift nor buoyancy. It is drag and should be called
that.

Hugh

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Hugh Haskell
<mailto://hhaskell@mindspring.com>

The box said "Requires Windows 95 or better." So I bought a Macintosh.
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