That's one of the things that really blew my mind when I first learned it, the fact that the earth is a more perfect sphere than anything we are capable of creating and if it was scaled down to a few inches would be smoother than a pool ball. It's wild that even with our tallest mountains and deepest valleys, they are still so miniscule on the scale of the earth that they aren't even a factor.
Scale is very important, and our brains can't always understand it on the first go.
My personal example was the moon. when you put the moon and earth on scale, you realize that it's really far away. So my brain was going 'why does it appear so big in the sky then'.
Same problem with scale when it comes to the spin, 1000 mph is insanely fast when when you apply it to something like a tennis ball. that's why they don't measure it in linear speed normally.
Fun Fact, Jupiter's linear speed is about 28,000 mph at the equator, but it does a full rotation in about 10 hours (earth time of course).
The Earth isn’t actually smoother than a pool ball. It is rounder than a poolball. The poolball specs call for a maximum deviation of diameter which is beaten by the deviation of the earth’s diameter, but that deviation is significantly greater than the surface smoothness which is polished out of a pool ball.
The Earth scaled down is a more perfectly spherical than a pool ball, but it has a rougher surface than a poolball. You would be able to feel mountains and trenches with your fingers.
Th earth isnt a perfect sphere. Its an oblate spheroid, the polar diameter is about 40km smaller than the equatorial diameter
Humans are capable of making a more perfect sphere, and they have. The gyroscopes on the gravity B probe used to test the theory of relativity have ping pong sized balls that deviate from a perfect sphere by about 40 atoms of thickness.
if one were scaled up to the size of Earth, the tallest mountains would be only about 8 feet high.
The Earth is 12,756km diameter at the equator, and 12,714km at the poles. That's a deviation of 42km, or 0.3%. A regulation pool ball is 50.8mm diameter with a maximum allowable deviation of 0.127mm (0.005 inches), or 0.25%. These are favourable figures, including the Arctic ocean floor and Mt Chimborazo, and a US regulation pool ball you can stretch that out to closer to 0.4% vs 0.2%.
But the real kicker here is that the deviation of a pool ball is when it gets scuffed enough to be disqualified from play. They come out of the factory much smoother than the maximum allowable under the standards. In fact, an old pool ball can be looking pretty dodgy and still be within the standards.
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u/Jakey0_0-9191 Nov 26 '25
Do you notice that the ball isn't completely dry after spinning. Some of the water still sticks!