Re: [Phys-l] Final velocity of bullets - Revisited

[jmarx@mcdaniel.edu]

I've found this thread quite interesting, so I asked my students if they
had seen this episode. They had, of course. The students recalled that the
bullets shot with a nearly vertical trajectory left an oblong-shaped hole
in the sand where they landed, suggesting that the bullets were, in fact
tumbling. (They also did not penetrate nearly as deeply as a bullet fired
directly into the sand. Bullets fired directly into the sand left nearly
circular holes.) Despite the oblong-shaped hole, I found the
tumbling-theory hard to accept because it was difficult for me to imagine
that the torque on the spinning bullet due to viscous drag (correct
phrase?) would slow the rotation rate down much at all, even over a
timeframe of tens of seconds. Brian Whatcott's post (below) seems to
support my intuition, but at the same time seems to contradict the
MythBusters "experimental result." How can this be resolved? Was the
experiment on the show so deeply flawed that their conclusions about the
bullet tumbling at some point on the way down be completely misplaced?
Having not seen the show, I'm sure there are many details of which I'm not
aware.

I look forward to more discussion on this topic.

Jeff


> At 12:43 PM 1/23/2007,  Oren, you wrote:
> > ////
> > Is the bullet still spinning when it reaches its maximum height?
> >
> > Or, put another way, 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
>
>
> The data I now have indicate that a bullet retains the majority
> of its spin momentum at the peak of the trajectory.
> It's also found that a back-first flight of a bullet is stable,
>   so that bullets may sometimes descend (blunt) tail first.
> This leads to a higher terminal velocity compared to the tumbling
> bullet's TV. (X2)
> This appears to be the major methodical weakness of the
>   Myth Busters' effort. They did not test a spun bullet in several
> of their setups.
>
>
>
> Brian Whatcott    Altus OK    Eureka!
>
>
> _______________________________________________
> Forum for Physics Educators
> Phys-l@carnot.physics.buffalo.edu
> https://carnot.physics.buffalo.edu/mailman/listinfo/phys-l