Why is there a tidal buldge on both sides of the earth caused by the moon?

Question

I know that the moon causes the tide but there is a tidal buldge on both sides...why?

Answer 1

The bulge on the other side is caused by centrifugal force caused by the fact that the Moon does not orbit the Earth, the Moon and Earth orbit each other around their common enter of gravity, which is below the Earth's surface but not at the center of the Earth.

Answer 2

The Earth would have a tidal bulge on both sides, whether it was rotating or not.

One way to think about this is using the gravitational potential.

A liquid planet will, in equilibrium, settle into the shape of a surface of constant gravitational potential. This is because the direction of lower potential is "downhill", so if the liquid surface is not going to flow, it have the same potential everywhere.

Without the Moon and without rotation, the gravitational potential surfaces are (approximately) spherical.

Without the Moon, but with rotation, the gravitational potential surfaces are oblate spheroids, bulging out at the equator.

With the Moon, and with rotation, the gravitational potential surfaces are mostly oblate spheroids, but with a prolate spheroid component that points at the Moon, superimposed.

The tides are caused only by this prolate component, because it causes the surface to move up and down as the Earth rotates (tides). The oblate and spherical components don't cause time variations.

Why is it this way? Well, it's the solution to Newton's equations for the gravitational potential. Basically, the downwards force on the side of the Earth far from the Moon is less than it would be without the Moon, because the presence of the Moon causes the center of the Earth to shift a little from the center of gravity of the Earth-Moon system.

Answer 3

On the side facing the moon there is a bulge toward the moon because that's where the force of the moon's gravity is greatest. On the side away from the moon there is a bulge away from the moon because that's where the pull of the moon's gravity is weakest.

Answer 4

Because the part of the Earth closer to the moon is rotating too slow, and the part of the Earth on the opposite side is rotating too fast: remember that the Earth and moon rotate about center of mass of their two body system.

Answer 5

gravity