Introduction to Free Fall
[Chapter
2 Objectives]
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To
a physicist, the term "free fall" has a different meaning than it
does to a skydiver. In physics, free fall is the (one-dimensional)
motion of any object under the influence of gravity only - no air
resistance or friction effects of any kind, whereas it is air
resistance that makes skydiving a hobby rather than a suicide
attempt!
You might think that since just about everything we observe
falling is falling through the air, that "physics free fall" must be
a pretty useless idea in practice. Not so! Any falling object's
motion is at least approximately free fall as long as:
- ... it is relatively heavy compared to its size. (Dropping a
ball, as in the picture at right, or jumping off a chair, is a
free-fall motion, but dropping an unfolded piece of paper, or the
motion of a dust particle floating in the air, is not. If you
crumble the paper into a "paper wad", however, its motion is
approximately free fall.
- ... it falls for a relatively short time. (If you jump off a
chair, you are in free fall. After you have jumped out of an
airplane and fallen for several seconds, you are not in free fall,
since air resistance is now a factor in your motion.)
- ... it is moving relatively slowly. (If you drop a ball or
throw it down its motion will be free fall. If you shoot it out of
a cannon, its motion won't be free fall.)
You should also note that an object doesn't have to be falling to
be in free fall - if you throw a ball upward its motion is still
considered to be free fall, since it is moving under the influence of
gravity.
[Chapter
2 Objectives]
BHS
-> Staff
-> Mr. Stanbrough ->
Physics -> Mechanics
-> Kinematics -> this page
last update July 27, 2001 by JL
Stanbrough