what happens to the water during low and high tide?



Like how does it shrink and expand?

In: Physics

It does not shrink or expand. The moon’s gravitational pull basically pulls all the large bodies of water with it as it goes around the earth. That moves the water around in each sea and ocean.

Gravitational forces from the moon and the sun pull at the water so it “bulges” in places and dips in others. https://youtu.be/fHO9J2LlXYw

It doesn’t actually shrink or expand. Everything in this universe with mass has its own gravitational pull. The more combined mass two objects have, and the closer they are to each other- the greater the gravitational pull between them. The Moon goes around the Earth. When the Moon’s location in relation to the Earth changes, the gravitational pull between the Moon and the giant bodies of water changes. That means that when the Moon is closest to a certain point on Earth, water on that side of the Earth is ‘pulled’ towards the Moon- this results in a high tide. This, in turn, means that on the other side of Earth you have a low tide.

This is long but

It just moves to another side of whatever sea or ocean it is a part of following the moon. Imagine a bowl halfway full of water. Now take that bowl and tilt it to one side. The water seems to rise towards that side and lowers on the other, sinking away. Tilt in the opposite direction. The water reacts similarly, with a high tide situation on the other side and a low tide situation on the original side.

To paint a better picture, though, since our Earth isn’t flat (Fight me.) keep the idea of water out of your mind for a second. Imagine a rubber band around your wrist. When you pull it away from your arm without pulling it off, you create space. Fill the space with water. This is a high tide.

Imagine having a ball and a rubber band. Set the ball on a flat surface in the middle of the rubber band, replacing your arm. Pull from both sides so that the rubber band stretches enough to touch the ball on two sides. Those two sides are low tide . the stretched sides are still high tide. The moon’s gravitational force is the pulling you’re doing, squeezing the water into the stretched out spaces.

Move your right hand closer to the ball and your left hand further away, just slightly. Your left hand represents your moon side. The tide is higher (holds more water) than any other place on this side because the pull from the Moon is strongest. The opposite side still has a high tide, though because your low tides are found where the band touches the ball.

It gets deeper than this. We can talk about those things when you’re 7, though.

Sorry in advance for format, etc. I’m on mobile. Edit to illustrate high tide on two opposite sides and for clarity.

Water doesn’t shrink and expand. It’s always the same volume. Because of the moon’s gravitational pull, water is constantly sloshing around the Earth like water in a cup. It’s not “high tide” everywhere on Earth at once, then low tide everywhere at once. It’s high tide on one side of the ocean and low tide on the other.

[Here’s a gif of the process.](https://cdn.shopify.com/s/files/1/1140/6118/files/TideAnimation.gif?v=1496773572) Basically the water is always bulging out towards the moon, but the Earth is spinning “underneath” that. So from the land perspective, the water goes up and down.