The two bulges are called tidal bulges. There are two
tidal bulges on opposite sides of Earth. One is beneath the moon and the
other is opposite to that. The one below the moon is thought of as gravitational.
It is produced by gravitational attraction between water molecules in the ocean
and the moon.
<span>Now, about the other bulge. Think about inertia and what
happens when masses rotate around a single point. Imagine yourself
swinging a bucket of any liquid with your arm in a circular gesture. Even as
the bucket goes over your head, the water is still held in the bucket and
doesn't splash all over you. This rotation creates a centrifugal force. A
similar event occurs during the lunar month as the earth/moon system rotates. The
moon orbits the earth, but the rotation axis for this orbit isn't earth's
center. Both the moon and Earth move during the roughly 28-day period it takes
for the orbit, and because of this, water in the ocean is thrown to the
outside, the same as the water in your bucket. The tidal bulge on the opposite
side of Earth from the moon is produced by this inertial effect, referred to as
centrifugal force.</span>
