Re: [Phys-l] Final velocity of bullets

[Jack Uretsky <jlu@hep.anl.gov>]

I suspect that this question is based upon a misconception.  "Terminal 
velocity" refers to the maximum velocity of a body falling under gravity, 
when mg=F, where m is the body mass and F is the air resistance, roughly 
proportional to the velocity squated.  It depends upon the mass of the 
falling body, as is evident from the equation.

A bullet is normally fired at a velocity far above terminal, and reaches 
its target with its velocity still far above terminal.

A bullet fired straight up will, of course, eventually reach a maximum 
height where its velocity is zero.  It will then fall "under gravity" and, 
depending upon a variety of factors, may or may not reach its terminal 
velocity in the course of its fall.

Incidentally, I am currently reading "The Trojan War" by Barry Strauss. 
He refers to scholarly opinion that ancient slingers could propel their 
stones with initial velocities of up to about 150 mph (much less, I think, 
than terminal velocity) and hit a target at a distance of 150 ft - with, I 
suppose, lethal effect, otherwise, why bother?
				Regards,
					Jack





On Tue, 23 Jan 2007, Brian Whatcott wrote:

> At 12:43 PM 1/23/2007,  Oren, you wrote:
> ...
> >  does a bullet reach terminal velocity before or
> >after the air friction stops the bullet from spinning and then produces
> >the tumbling?
> >
> >Oren Quist, South Dakota State
>
> I cannot speak directly to the question. I recall that the
>   ogival bullet nose or round nose for that matter, is
> advantageous from the point of view of low drag coefficient.
>
> But this shape has a center of gravity aft of the center of
> pressure, so it is only the spin that holds the bullet "on point"
>   as it were. The spin substitutes precession, nutation and
> (sometimes) a helical initial trajectory for tumbling.
> It is perhaps for this reason (I cannot recall clearly) that
> some competition bullets have square noses.
>
> Bullets with hollow tails (rather than hollow noses) or better,
>   boat tails can also help dynamic stability by placing the
> CofG further forward.
>
>
>
> Brian Whatcott    Altus OK    Eureka! 
>
>
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