How is the Three Gorge Dam made in China slowing down the speed of the Earth's rotation? What are the side effects?

 

The largest dam in the world, this thing can hold up to 42 billion tons of water in its reservoir.

Now, you might think that water is just water, and it doesn't matter where it is. But you'd be wrong.

Water has mass, and mass has gravity. And gravity affects how fast the Earth rotates around its axis.

You see, the Earth is not a perfect sphere. It's slightly flattened at the poles and bulging at the equator.

This is because of the centrifugal force caused by its rotation. The faster the Earth spins, the more it flattens out.

But when you move a lot of water from one place to another, you change the distribution of mass on the Earth's surface.

And that changes how much centrifugal force there is at different points on the planet

The Three Gorges Dam has moved a lot of water from lower altitudes to higher altitudes, closer to the Earth's axis of rotation.

This means that the water in the reservoir has less centrifugal force than before, and it pulls more on the Earth's core. This makes the Earth more round in the middle and more flat on the top.

And what happens when you make something more round?

It slows down its rotation.

That's right; the Three Gorges Dam has slowed down the Earth's rotation by increasing its moment of inertia.

The moment of inertia is a measure of how hard it is to change an object's angular motion.

The more mass an object has near its axis of rotation, the higher its moment of inertia, and the slower it spins.

Now, the spin is not much slower. According to NASA scientists, the Three Gorges Dam has increased the length of a day by only 0.06 microseconds.

That's 0.00000006 seconds. You can't even notice that with your naked eye.

Maybe in an eon, we'll have an extra second to spare. Thanks, China!