purpose of the moon

[Gerianne]

I always thought gravity was in the earth.
There was a program on the Discovery Channel that was about gravity's source being the moon.

[lvstephanie]

Every object that has mass has a gravitational force. Even you have a gravitational force! However, the amount of mass and the distance between any two objects dictate the amount of gravitational force that is felt between the two objects. Since Earth has a lot of mass, that is why Earth's gravitational force holds other objects "down". The moon also has its own gravitational force, but much less than that of Earth since it doesn't have as much mass as Earth. This is why when you watch videos of men walking on the moon, they seem to float; the amount of gravity that the moon exerts on them is less so that they don't get pulled down as easily.

But as I mentioned before, mass and distance effect the amount of gravitational force. This is why on Earth we feel pulled down by Earth and not up towards the moon, or even the Sun which although has a larger mass than Earth is also much more distant to us than the center of the Earth. Yet even with the Moon being more distant and less massive, it still exerts some gravitational force on us as well; we just don't tend to notice it. The best way to see the Moon's gravitational force on terrestrial objects is in the ocean tides. Even though Earth's gravity holds the water down in the ocean, the moon's gravity effects how the water moves around in these ocean depths thereby causing the water to shift in what we know as tides. You can mimic this by putting some iron filings on a table and then swinging a magnet above them. As long as the magnet is not too close, the Earth's gravity will hold those filings on the table. Yet the magnet swinging above exerts a magnetic force that causes the filings to shift in different patterns on the table.