Great question! And the answer is that, in a sense, gravity /is/
acceleration! You've probably heard of the "force of gravity," and you
may have heard of the equation "F=ma." What this equation means is that
the force on an object is the same as the mass of the object multiplied
by how much it's being accelerated. The thing about gravity is that it
has its own number for the "how much it's being accelerated" part, and
that number is the same pretty much anywhere on a planet. For gravity
on the Earth, that number is about 9.81 (m/s^2).
Since that doesn't change anywhere on Earth, the only thing that
changes the force of gravity (as long as you're on Earth) is the mass
of the object (which is a lot like how much it weighs). For example, if
you were to drop two balls off of the top of a building at the same
time, you'd see that they both accelerate exactly the same way, no
matter how much either one weighs!
The thing that will change that number (for the acceleration of
gravity) is how big the planet is that you're standing on. On the moon,
for example, the acceleration of gravity (and the force of gravity) are
about 1/6 of what they are on the Earth. So you would actually fall
slower if you jumped on the moon than on the Earth. This is because the
moon is much smaller than the Earth. But on a bigger planet than Earth,
the acceleration of gravity would be bigger, and you'd fall faster.
Hope this answers your question!
(published on 10/22/2007)