Question

The Equilibrium theory cannot be used to explain diurnal tides (that have only one high and low per day ), but it can give us insight into tides that have two highs and two lows in a day, and into combined tides produced by the sun and the moon:

Tides with 12 hr 25 min. periods. Explain why the semi-diurnal period is not 12 hr (the earth rotates once around its axis in 24 hrs, doesn't it?)Use example given in lessons about why lunar tide is 24 hrs 50 min (and divide it by half)

Answer 1

The two high tides and two low tides each day occur because the Earth rotates every approximately 24 hours and the Moon orbits Earth, causing a slightly more than 12-hour interval between the tides due to the Moon’s movement in its orbit each day.

Step-by-step explanation:

To understand why there are two high tides and two low tides each day, we need to consider the Earth's rotation and the Moon's orbit. If Earth did not rotate and the Moon was stationary, the tidal bulges, which are the areas of high tide, would remain at the same locations on Earth. However, because the Earth rotates approximately every 24 hours and the Moon also orbits Earth (in the same direction as Earth's rotation) approximately every 28 days, the locations on Earth experience the high tide positions not after 12 hours (half the Earth's rotational period), but approximately after 12 hours and 25 minutes. This slight delay is caused by the fact that as the Earth turns, the Moon moves in its orbit each day, meaning Earth has to rotate a little more than half of its circumference for a location to align with the next tidal bulge.