How is the earth spinning, as in what set it into motion? Why hasn’t it stopped spinning yet/ when will it stop? Has there been any noticeable decline in spin speed?
In: Physics
In space you have dust. The dust is made up of particles. However small they are, they still have mass and, therefore, gravity. The gravity pulls those particles toward each other.
When you have a lot of particles, they all can’t fall into the exact same spot. Imagine a cloud of particles and a point in the middle. All the particles want to occupy that spot, but they will bump into each other, knocking each other off course. As they pass by that spot, they will turn around and make another attempt. When you have all the particles doing this, in the same direction, now the entire cloud of particles is spinning around that spot as they try to move toward that spot.
Eventually, particles will begin to occupy this spot, or otherwise stick to other particles occupying this spot, creating a clump. This clump will inherit the motion of the particles that make it up. Since the particles are spinning around that spot, so will the clump, even as it gets bigger and bigger, becoming a planet.
Without interference, the planet will spin forever.
But the Earth has interference: the moon. The moon pulls at the Earth. If the Earth was entirely solid, this wouldn’t be an issue, but is has oceans. The liquid nature of the oceans means they can flow over the Earth. As the Earth spins away from the moon, the gravity pulls the oceans back toward the moon, this action works against the spinning of the Earth and slows it down. But it is very slight: we have only “lost” 1.7 milliseconds in a century.
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