Bill Pragnell <bil### [at] hotmailcom> wrote:
> Hollywood gets projectile momentum transfer wrong all the time. Every 
> time somebody gets shot by any kind of weapon, for a start.

  Yes, it's funny how Hollywood physics are so skewed while still not
appearing completely wacky to the layman.

  For example, the faster the bullet, the farther it throws the person
who is hit by that bullet. In reality it's almost the opposite: The faster
the bullet, the less effect on the victim. The bullet just goes through
like a needle, and only little of its kinetic energy is trasnferred to
the victim itself. A slower bullet, however, transfers its kinetic energy
more to the victim because the body of the victim gets to slow down the
bullet, even so much that it might not even get through. In that case
the entire kinetic energy of the bullet is transferred. However, even in
that case the amount of kinetic energy is quite small compared to the
mass of an average person (the bullet is, after all, very light) and it
will not cause too much of an effect. Any minor effect will more likely
be overwhelmed by muscle spasms caused by the pain, which may cause the
victim to move to any random direction.

  (In some cases, if a fast bullet goes through, the jet effect caused
by the blood in the exit wound might even cause a movement towards the
shooter, not away from him... Still quite small, though.)

  Of course if we think about it in newtonian terms, if the victim gets
thrown back several meters, so should the shooter be too. The exact same
kinetic force is applied to the shooter, to the opposite direction.
(Well, technically speaking *more* kinetic energy is applied to the shooter
than to the victim because the bullet loses some kinetic energy during its
flight due to air friction, so if anything, the shooter should fly farther
back than the victim.)

  Then there are all those sparks. Bullets always send sparks when they
hit almost any surface. Of course real bullets don't, because bullets are
usually made of metals (such as copper) which do not spark even if they
hit some other metal. The movie makers themselves know this because they
can't get the sparks with real bullets but they must cheat (at least in
older and cheaper movies they used specially constructed "bullets" which
send sparks when they are broken).

  Those sparks have always bothered me. They make the scene unrealistic
and overboard. They don't add to the intensity of the scene.

  For a superb exception to this, see the beginning scene of Saving Private
Ryan. It's super-realistic. No bullet sparks. Yet the scene is extremely
immersive and intense. You can really *feel* the danger posed by those
bullets which you can't see but which are coming from everywhere.

-- 
                                                          - Warp

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