Why do we experience 2 high and 2 low tides almost every day?

Question

HINT: the moon does not rotate around the earth once every day.

Answer 1

The gravitational pull of the moon stretches the Earth's hydrosphere into an ellipsoid. It bulges both towards and away from the moon - towards it because the water on the near side is being pulled towards the moon, and away from it on the other side because the gravitational pull of the moon is lowest on the far side.

So you get one high tide as the moon passes overhead, and another as it passes on the other side of the Earth, with low tides in between. And you're right, it's the motion of the Earth, not the moon, that drives the tides.

Answer 2

The moon doesn't orbit the earth once every day, but because the earth spins - the moon passes overhead every day. It also passes opposite of the earth once every day. When ever the moon is at either of these points, we have high tide. So since it is at both one once a day - that makes 2 high tides.

And a high tide is always preceeded by a low tide because that is when the moon is 90 degrees away from us - and it does this twice each day - one to the far east of us, and other to the far west of us as it passes overhead - giving 2 low tides.

Answer 3

It has to do with the gravitational pull of the moon.