PDA

View Full Version : How to calculate perceived gravity when rotating?



Vultur
2008-Nov-06, 09:57 PM
Where can I find the formula for the acceleration felt by someone inside a hollow sphere or cylinder that is rotating, or the acceleration that works against gravity on a spinning planet?

Fazor
2008-Nov-06, 10:02 PM
Well, just because it sounds like a homework question, I'll just point you towards a helpfull search term; centrifugal force.

Vultur
2008-Nov-06, 11:20 PM
OK, thank you.

It isn't homework, actually; I was reading the "pellucidar" books and wondered if Earth's rotation would make a noticeable "gravity" inside.

Hornblower
2008-Nov-06, 11:21 PM
OK, thank you.

It isn't homework, actually; I was reading the "pellucidar" books and wondered if Earth's rotation would make a noticeable "gravity" inside.

Inside of what?

grant hutchison
2008-Nov-06, 11:31 PM
Inside of what?Inside the hollow Earth of the Pellucidar books, I imagine. :)
The answer is "not particular noticeable", Vultur. At the equator, on the surface of the Earth, the centrifugal pseudoacceleration is about a three-hundredth of a gravity. Inside a hollow Earth it would be everywhere less than that, and of course it would also point in the wrong direction everywhere except at the equator of the spherical cavity.

Grant Hutchison

01101001
2008-Nov-06, 11:32 PM
Earth's rotation doesn't noticably affect a person's weight on the rotating equator versus spinning pole. It's about a pound/half-kilo for a big man.

LotusExcelle
2008-Nov-06, 11:33 PM
Step one: Drop bowling ball on foot. If it hurts its about 1g.

grant hutchison
2008-Nov-06, 11:46 PM
Here's something I wrote a while ago, breaking down the different components of the weight difference between pole and equator.


... if the Earth improbably stayed an oblate spheroid despite ceasing to rotate, its effective equatorial gravity would increase by 0.35% as a result of the withdrawal of centrifugal force; if the Earth relaxed back into a sphere when it stopped rotating, its effective equatorial gravity would increase by 0.4%, because of the combined effect of withdrawing centrifugal force and moving closer to the centre of mass.
...
(If you travel from the pole to the equator on the real rotating Earth, your weight increases by 0.5%: the pole is close to the centre of mass and unaffected by centrifugal force; the equator more distant from the centre of mass and maximally affected by centrifugal force.)Grant Hutchison