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Comment by mcswell | Hacker News Reader

Thank you--the diagram you link is a better explanation of whey the tide "bulges up on the sides of the Earth closest to and farthest from the Moon"--the article left this entirely unclear.

In particular, I could understand how two satellites connected by a cable would result in the cable being stretched. But I still find it hard to wrap my mind around the fact that we get a high tide where the Earth's gravity and the Moon's add (the far side of the Earth from the Moon), but we also get a high tide on the opposite side, where the Moon's gravitational pull is subtracted from the Earth's. The centrifugal force is (I think) a much better explanation. (I realize physicists don't consider that a force, but...)

So yes, tides really are weirder than I think.

(The other facts in the article were actually familiar, e.g. the fact that the tides in Hawaii are quite small, because it's not far from an amphidromic point.)

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Tides aren't caused by centrifugal force but by differing gravity. You would be ripped apart by tides falling straight into black hole.

The near part of Earth experiences more gravity from the Moon, the far part less. The Earth moves in the center so the water bulges on the ends. Important part is that the Earth pulls things out their natural orbits.

With circular orbits, gravity and centrifugal force are balanced so could be considered difference on centrifugal force. But that isn't true for all orbits.

Simple illustration of what you are explaining in 1D. Imagine a simplified Earth:

Water -- Ground -- Water

Now let's add a Moon with gravitational pull. The pull stretches the system, because gravity is stronger the closer you are to the Moon.

Water ---- Ground ---- Water -//- Moon

The water is farther away from the ground on both sides now, since both sides stretched.

so why is left water further away from ground? this example make 0 sense

The Earth is being pulled away from that water, just as the water on the right is being pulled away from the Earth.

But the water on the left is being pulled by everything to the right of it, moon, earth, other water. Why is it left behind? Every single thing is being attracted by the same centre of gravity on the right of the earth

It's further away so it's pulled less, so it shifts less.

"You would be ripped apart by tides falling straight into black hole." I'm aware of that--Larry Niven "Neutron Star". (The Puppeteers reportedly wouldn't have understood, though.) That still doesn't explain why the water bulges at the side of Earth away from the Moon, because that water would be attracted toward the Moon just as much as the rock it's next to. (There's a trivial difference in mid-ocean, where the water ranges from direct contact with the ocean floor, to a few miles above it. But that's not the same as the gravitational difference of thousands of miles between the Earth's center of mass vs. the far edge.)

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