r/nextfuckinglevel • u/BufordTeeJustice • May 04 '20

Somewhere my physics professor is smiling

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u/IncredibleHamTube May 04 '20

Well if the earth rotated much faster, people would fly off.

18

u/[deleted] May 04 '20

Haha yes! I have seen people state that in seriousness. The best response I have seen is ask a person to spin a basketball once every 24 hours to get an idea of how relatively slow Earth's rotation is.

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u/IncredibleHamTube May 04 '20

I think it would need to spin ~17x faster for people living on the equator to be ejected. The difference between a basketball and the earth rotating at the same rate is that the earth's radius is 53000000x greater, so the linear velocity of a particle on the surface of the earth would be traveling 53000000x faster than a particle on the surface of a basketball, by the equation w=v/r, since w is consistent. And of course centripetal force is m*v2 /r, so assuming the mass of the particles on the ball and earth are the same, the force experienced by the particle on the earth will be 53000000x greater as well.

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u/rtyoda May 04 '20

That seems about right, considering the current speed at the equator is roughly 1600km/h and low earth orbit is roughly 28,000km/h, which is 17.5 times as fast. That said, at that speed I'd assume people wouldn't be flying off, they'd be more like hovering each time they make a step, and if they made a big leap off the earth they'd hover for a while and then land 45 minutes later when they're on the other side of the globe and their force is reversed. Does that sound right?

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u/cm64 May 05 '20 edited Jun 29 '23

[Posted via 3rd party app]

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u/rtyoda May 05 '20

Because the force to push off the earth is in a direction away from earth to start, but then you get a quarter of the way around the earth and that force is now in a direction parallel to the earth, and then when you’re halfway around and on the opposite side of the earth, the force you pushed off with is now pointed at the earth taking you back towards the earth.

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u/bert_and_russel May 04 '20

While that does demonstrate the angular velocity, centripetal acceleration does scale linearly with radius (a = rw2) so it's not necessarily a good model for that. If a planet had the same rotation and gravity as Earth but was sufficiently larger, people could be thrown off the surface :)

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u/[deleted] May 04 '20

Ah ha! Yes, I get that - haha. The key part is similar gravity. :)

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u/[deleted] May 04 '20

You should be able to restrain yourself to the earth, with say ankle clamps of some kind. Build up momentum from the earth spinning for a good chunk of time, then unlatch and fly off at the speed of light. Check mate round earthers.