How can the tides of one place have a difference of one or two feet, while in some places the tide difference is nearly forty feet?

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How can the tides of one place have a difference of one or two feet, while in some places the tide difference is nearly forty feet?

In: Physics

Imagine bodies of water are children’s sand pits. The oceans are huge sand pits. The effect of gravity caused by the sun and moon to form tides pulls water upwards. This is like taking all the sand and making it a single large pile. With a large enough sand pit, this pile can be taller than you are!

Smaller bodies of water with limited connections to larger water (Mediterranean Sea) are much smaller sand pits. Even with gravity pulling the water up, you can’t make a very tall pile so the tides are limited.

If there was no land at all to get in the way, the change in tides would be highest at the equator and basically zero at the poles, but when you have continents getting in the way of a planet scale wave that wants to follow the moon around, the inertia of the water, and restrictions to flow, have a huge impact.

A big reason is the specific local geography. As the whole ocean goes up and down, it goes in and out of bays, estuaries, etc. As the bay narrows, you have this rush of water which can’t just stop in an instant (i.e. momentum). It has to go somewhere (water is incompressible on these scales), so it literally piles up on top of itself. The funnel shape accentuates the tides. Also depends on the shape of the local sea floor, etc. In some places, this can actually result in a wave that just sits in one place.