Gravity and Spin

Okay, if the Earth stopped spinning…(Ignoring any catestrophic results)…would we weigh more? Does the centifical force of the Earths spin, counteract any of its gravity?

Heaven…One to beam up!

Dude, your majesty, do you mean:

Main Entry: centrifugal force
Function: noun
Date: circa 1721
1 : the force that tends to impel a thing or parts of a thing outward from a center of rotation
2 : the force that an object moving along a circular path exerts on the body constraining the object and that acts outwardly away from the center of rotation <a stone
whirled on a string exerts centrifugal force on the string>

“And on the eighth day, God Created beer
to prevent the Irish from taking over
the Earth.”

That would be the force of debate. I try not to type words I cannot spell…Cecil needs to put a spellchecker on this thing…

Heaven…One to beam up!

Those of us at the Equator would weigh less. Those at the north and south poles would not. Those between would weigh less in inverse proportion to latitude, according to some arcane vector trigonometry. No one would notice except the pendulum clock repairmen, and the guys at NASA. (Well, if it happened all at once, we would notice slamming into the walls at a thousand miles an hour, no sunrise, weird weather, and stuff.)


There is no national science just as there is no national multiplication table; what is national is no longer science.
– **Anton Chekov, ** (1860 - 1904)

Those ‘effects’ where the results I was ignoring… I had forgotten about the poles that would make sense…now…
How much of a difference would it make?

Heaven…One to beam up!

yeah, I am just trying to help, I realize I may have come off stuck up or something. Didn’t mean to, just trying to avoid any confusion for future respondants…
I of course, think that if we could somehow suspend the catastrophy of the earth stopping spinnig-didn’t that happen in the bible like where the Sun stopped in the sky?-we would weigh a hell of a lot more.
On the other hand, I think that once you pass a certain point centrifugal force is negated by the sheer mass of the object you are in prximity to. that is a real <font size=+3>WAG</font> so all you smart guys who actually know, don’t tear me up.
Peace. :smiley:

“And on the eighth day, God Created beer
to prevent the Irish from taking over
the Earth.”

Using ZenBeam’s calculation in the thread
you’d weigh about half a percent more, at the equator.


Also, the Earth is currently an oblate ellipsoid (slightly flattened along the rotational axis) because of the centrifugal force. If the earth stopped spinning, it would pop back into a (near-) perfect sphere. So people at the poles would weigh less.

There are a lot of side effects that occur when you stop the earth spinning. This is why when Joshua needed to lengthen out the day to search for the Hittites (or whoever it was) he had the sun go backward rather than mess with the earth’s rotation. Always go for the simplest solution to your problems.

“pluto … a seriously demented but oddly addictive presence here.” – TVeblen

Of course between moving the Earth and moving the Sun…the Earth is easier to move…so probably God stopped the Earth and didnt move the sun…

Heaven…One to beam up!

This question has already been addressed by Cecil:


The Earth’s spin has nothing to due with it’s gravity holding you down. If we were to break the rotation slowly enough so we don’t fly off you would still be glued to the surface.


At the equator yes; at the poles, no. Yes, by a very small amount.


Careful guys, you’ll get TomDark over here with his Velikovskyism, and then we’ll never get him to shut up. See


I don’t think so (about weighing less). The reason the earth is oblate is because gravity is less at the poles - i.e. it is being counteracted. If that counteraction were removed, then full gravity would be felt, thus weight increase.


Reread the OP. Yes, the gravity is independent from the spin, if you consider gravity as purely the mutual attraction of two bodies. However, the effective weight will be affected by the spin. Weight is a measure of more than just gravity.

Now you’re going to make me link to RM Mentock’s thread on how to measure the center of the earth. I refuse to inflict that on you. :wink:

Hey! If you can link to Tom’s, you can link to mine.

'Course, what you really want to do, is read Cecil’s column. It points out that you have the above 'zactly backwards.


Why would there be a difference at the poles? As someone posted - if the earth stopped spinning, then it would pop back into the shape of a nearly perfect sphere.

If that were the case, then the poles would be just as far away from the center of mass as the equator (as would be any other point on the surface), and gravity would be exactly the same at every point.

Am I missing something?

No, you’re not, except for: why do you think you are?


In keeping with Irishman’s reply, it should be also mentioned that, conversely, if the earth turned fast enough, we could be thrown from the surface.

How so? Cecil says the spinning tries to throw you off, and without spin you stick on better. So do I. Cecil does say that the spinning flattens the poles. Yes, and it stretches the equator. Hand in hand. Take a rubber ball and push on the top, the equator expands and the poles contract. Same diff. (See picture of Saturn for good example.)
It’s more striking on Saturn, but that’s the same effect on Earth (minus the rings).

Where Cecil bridges on… misdirection is his comment about the gravity evening out. Yes it would, bringing the polar weight down a hair and increasing the equatorial weight a hair. What do I have backwards?

Yes, the fact that since it is spinning now, there is currently a gravitational difference. (Actually, it’s inertia, but it opposes gravity.)

I agree that the current spin of the earth causes there to be a perceived diference at the poles, I just didn’t understand why people were saying it stayed in effect when the spin was gone.


Which people are saying that it stayed in effect? (Well, if you want, I’ll say it. The equatorial bulge probably wouldn’t subside immediately. In fact, in the early sixties, the excess bulge of the equator --beyond what could be accounted for by rotation-- was attributed to the delayed response to the earth’s slowing, and that delay indicated that the earth’s viscosity was too high to support mantle convection–one of the major arguments against plate tectonics. That argument has been discredited, of course, but there would still be some delay.) But who else was saying it?


The earth’s rotation does not counteract gravity at the poles. If the earth were to stop rotating, the poles would be less flattened, so someone at the poles would be farther from the center of the earth–and would weigh less, as Cecil points out. Your comment

is not true. Gravity is actually greater. And the centrifugal force doesn’t counteract it there, so people weigh more at the poles.