Steve -
All objects feel air resistance. I am
guessing the quotes you've heard about air resistance being
insignificant for a bullet refer to a bullet shot horizontally at
something. In this case, the bullet reaches its target and stops so
quickly that there is not enough time for air resistance to have much
of an effect on it.
However, if you shoot a bullet straight
up, it will take quite a long time for it to fall again. When the
bullet reaches the top of its trajectory and starts to fall again, the
speed that it gains is due only to gravity. At some speed, the force of
air resistance (which depends on velocity) will equal the force of
gravity (which does not depend on velocity). This is what's referred to
as 'terminal velocity.' All falling objects have a terminal velocity.
The smaller the object is, the higher the terminal velocity. For a
bullet, one estimate that I have read for terminal velocity is around
300 ft/sec (about 200 mph). Since that's a lot slower than a bullet
leaves a gun nozzle, it seems that the air resistance really will have
a big effect on the speed of the falling bullet.
To read more about this, look .
-Tamara
(published on 10/22/2007)