Re: why does the earth orbit around the sun?

Vanessa, the quick answer's that Earth & Sun mutually
attract one another: the force of gravity is acting between
them, causing them to orbit around a common center. In fact,
the mass of the Sun is vastly greater than that of the Earth,
so the "common center" is really a point very near the Sun's
center of mass! However, it's interesting that this "center of
gravity" point ISN'T exactly at the center of the Sun: the Sun
DOES "wobble" ever so slightly due to the gravitational tug of
our tiny little light-weight Earth. In fact, this "wobble" can
be seen in stars with planets orbiting around them - and that's
the ONLY way we know (so far) that the planets are even there!

(BTW, to understand why planets orbiting the Sun don't simply
"spiral in" and fall into the Sun, remember that these planets
already have their own momentum: at some time during creation,
these planets were given a "kick", causing them to have motion
in space. And as we know from Newton, any body which is moving,
tends to continue moving with the same direction and speed till
some force acts to change that motion! Well, the gravitational
attraction of the Sun DOES cause each planet to "fall into" the
Sun: however, the momentum each planet was "born with" is JUST
sufficient to counteract that in-pulling force each time the
planet goes around the Sun: in effect, a planetary orbit is a
delicate dance between gravitational acceleration from the Sun
continually acting on the planet, and that planet's momentum...
And you guessed it: if a planet's initial momentum ISN'T enough
to "balance" the tug of Solar gravity, it WILL fall in!)