Gravity - Spinning = differences?

[fantastical]

If the inward-gravitational force is equal across all points on Earth, and different points on Earth spin at different rates, depending on the lattitudinal position, what are, if any, the differences between bodies with this difference of (inward gravity) - (outward spinning)?

[tony1941]

Yes, the resultant gravitational force will vary with latitude.  I seem to recall that the measured value of "g" is quoted for a specific location.  It's all in my copy of "Physical & Chemical Constants" (Kaye & Laby) which is on my desk at work, but I'm out on site tomorrow so can't check the reference.  I'll have a look on Tuesday and reply again.

[mibn2cweus]

Effective gravity on the equator is reduced by the rotation by about 1/3 of a percent.
Search:  reduction of effective gravity by the Earth's rotation

[mibn2cweus]

In all, things weigh about 0.6% less on the equator than at the poles; best to use a balance scale.

[kempie]

Also (on average) g at mean sealevel at the poles is about 0.53% greater than the equator.

These two figures would indicate that a person weighing 80 Kg at the equator should see an increase in weight of around 700 gram(me)s at the poles.

[kempie]

oops... stepped on your toes there mibn2cweus

[mibn2cweus]

didn't hurt a bit

[kempie]

That must prove that we are not at either of the poles. ;-)

[mibn2cweus]

I'd say that's likely.  I appreciate your concern.

[mibn2cweus]

Don't you just hate it when you go to post to the last post then when you get there someone beat you to it so they think your posting to them?

[fantastical]

So there will be more gravitational (inward) force exerted on bodies at the poles than at the at the equator, since this inward force acts primarily to offset the centrifugal force of Earth's rotation and keeps things "planted" on this planet?

If there are x units of inward force required to offset the centrifugal (outward) force, then x is simply the difference of outward - inward. If the inward value (g) remains relatively constant across all points on Earth, but the outward value (c) changes dependent on lattitudinal position (l), x becomes a product of (c * l) - g, with "l" probably being an exponent of some constant. For simplicity's sake:

(c*l) - g = x, where g is (close to) a gravitational constant and x is the residual difference of force needed to remain on this planet, dependent on l.

Consider x is not the same for all things on different positions on Earth (depends on l). This means forces are not in equilibrium across all things on Earth. There are different forces acting upon a person in Borneo than there are upon those in Svalbard. Could the dynamics of our celestial propeties not open a huge can of worms? What happens if the poles swap with each other? What happens if other satelites become entrapped in our gravity like the moon is, somehow changing our gravitational force? How many other "worms" could be identified?

[mibn2cweus]

 Simply stated, the gravitation pull inward toward the Earths center, (due to the Earth's mass), is the overwhelming force, greater than 99% of the total.
 The combined outward forces of Sun, Moon, and Earth's rotation are less than 1% of the total.  Centrifugal force due to the Earth's rotation only effects objects moving along with the Earth at the same velocity.
 The gravitational pull of the Earth is slightly greater at the poles.  This variance in gravitation pull is significantly greater than the variance due to rotational forces.
 The overall variance in the weight of an object measured at any two points on the Earth�s surface is less than one percent.

[JudgeJ]

I believe that the gravitational force upon an object is greater at the poles than at the equator because the earth is slightly flattened at the poles. This makes the surface at the poles nearer to the centre than the surface at the equator. Gravity varies with the square of the distance from the centre of the object exerting the force.

The swapping of the poles mentioned should not effect these calculations as it refers to the movement of subterranean magnetic material currently located near to the geographical North Pole. 

[CT]

All of these answers are very true but, another factor is missing. Density of underlying matter has a large effect on gravitational pull, in comparison wtih centrifugal effect. Denser areas of the crust and underlying mantle increase the local gravitational pull. Conversly, less dense areas will have lower gravitational pull. These effects are measurable over areas such as mountain ranges.

[tony1941]

try  yet again - Ive just discovered that the tab key submits the post!!

Three measurements

Teddington, 1969      9.811819

Sevres, 1969            9.809260

Washington, 1969     9.801024

all in metres/sec^2.  As you can see, the difference is very small, but definitely decreases near to the equator.

[Hamish]

The problem is that there is no such thing as centrifugal force. Only centripeatal. A force is defined as mass x acceleration. Motion tangental to the earths rotation has no associated acceleration and therefore has no associated force. The force acting on a rotating body is centripeatal force, this is defined as the liniar veolcity squared over the radius of rotation times the mass. This, in the case of the earths rotation is gravity, ie its the force which prevents us spinning out into space.

I think that the confusion comes from spinning things about ourselves and feeling a tug on our arms. This happens because every action has an equal and opposite reaction. However when considering the spinning body, we only consider the forces acting on it, it the force keeping it on an arced path rather than a straight one. This is really the opposite to that felt on you arm when spinning something, it the pull you exert.

I feel I havent expalined this too well, perhaps discussion of it will help?!

[kempie]

As Hamish has pointed out, the correct terminology which should be used is "centripetal force" and "centrifugal reaction".

[mibn2cweus]

When I said, �Stated simply . . .�, I didn�t realize how much I meant it.  Neither centrifugal �force� or centripetal �force� is a force qua force.  That is, they are not causal.  These terms are used to describe the opposing mechanisms which preclude an object from or permit an object to travel in a straight line.  In this case centripetal �force� is gravity and centrifugal �force� is the earths rotation.