Is gravity weaker at the equator?

[Kwizard]

Well, of course it is because of centripeal force, but by how much?

I've heard that the difference between 1.0 G's and 0.9 G's is pretty hard to notice - and the gravitational difference between London and Caracas is bound to be far less than that. Anyone have info on this?

[Darth Wong]

Why don't you try and calculate the difference?

[Lord of the Abyss]

After a quick google, there's this : Link

To derive the centrifugal acceleration on the equator (i.e. the force in Newtons on one gram mass, rotating with the Earth), we calculate in meters and seconds


v2 / r = (465.1)2 / 6378000 = 216318 / 6378000 = 0,03392 m/s2
Comparing this to the acceleration of gravity--say 9.81 m/s2--it is only 0.00346 or 0.346%. Effective gravity on the equator is reduced by the rotation, but only by about 1/3 of a percent

[Melchior]

Well, of course it is because of centripeal force, but by how much?

Isn't it also because Earth, not being perfectly spherical, is larger at the equator?

[Admiral Valdemar]

Isn't it also because Earth, not being perfectly spherical, is larger at the equator?

That too. There's a reason why we launch rockets from as close to the equator as possible since it saves on fuel.

[drachefly]

Most of that is that orbit requires angular momentum, and you get quite a bit for free if you're near the equator. The other parts of the gravity reduction (distance from core, for example) aren't nearly as important.

[Wicked Pilot]

I didn't feel any lighter when I crossed the equator.

[Admiral Valdemar]

Most of that is that orbit requires angular momentum, and you get quite a bit for free if you're near the equator. The other parts of the gravity reduction (distance from core, for example) aren't nearly as important.

True, it mainly is down to the speed the Earth gets at the equator, but every little helps when you'rein that business. Would be nice to see this anti-gravity technology mature fast to make it even easier.

[Kuroneko]

Most of that is that orbit requires angular momentum, and you get quite a bit for free if you're near the equator. The other parts of the gravity reduction (distance from core, for example) aren't nearly as important.

They aren't as important, yes, but still significant enough. If the Earth were spherically symmetric with the mean volumetric radius, the effective gravity at the equator would be 9.7888m/s², compared with the actual 9.7804m/s². That means the effect of the bulge is 25% that of rotation. If launches near the equator are economically worthwhile, a quarter of that difference would be significant for such applications.

[j1j2j3]

One Thing I remember from Uni is that although the centrifugal force at the equator decreases gravity a bit, that same centrifugal force increases the mass at the equator which causes gravity to increase a bit canceling each other out.

There also was another factor that I can't remember. Anyway from what I remember the net gravity at the equator was a bit less than at the poles.

I know this won't help but, I'm sure a little bit of research will reveal all.

Oh and the last factor was distance from the center of mass will increase at the equator but was negligible. I think. Heh, I'm drunk. Sorry.

[Broomstick]

So.... where is gravity least: on the equator, or on top of Mt. Everest? Everest being furthest from the center of the Earth, and not too far off the equator. Is the extra distance from the core significant?

[Kuroneko]

One Thing I remember from Uni is that although the centrifugal force at the equator decreases gravity a bit, that same centrifugal force increases the mass at the equator which causes gravity to increase a bit canceling each other out.

That's just plain false. While the centrifugal force does cause a bulge, which does increase the mass near the equator, this bulging also causes elevation relative to Earth's center to increase. As a result, the effect of both the centrifugal force and the bulge is to decrease local gravity. What you may be referring to is that a spherical Earth would have lesser gravity at the current equatorial radius if there was no bulge--that is true, but irrelevant. If there was no bulge, then assuming the Earth would still have the same mass and density, what it should be compared to is a ball of Earth's mass and volumetric mean radius instead.

So.... where is gravity least: on the equator, or on top of Mt. Everest? Everest being furthest from the center of the Earth, and not too far off the equator. Is the extra distance from the core significant?

Gravity at the peak of Mt. Everest is less than that of equatorial sea level, as it is both farther away from the center and the mass effect of the Himalayans should still be less than that of the equatorial bulge. Using the Equatorial and polar radii a = 6.3681e6m and b = 6.3568e6m, distance from the center to the peak of Mt. Everest (φ = 27°59′16″) becomes r = 8844.43m + [a²cos²φ+b²sin²φ]^{1/2} = 6.3745e6m > a.

[drachefly]

Most of that is that orbit requires angular momentum, and you get quite a bit for free if you're near the equator. The other parts of the gravity reduction (distance from core, for example) aren't nearly as important.

They aren't as important, yes, but still significant enough. If the Earth were spherically symmetric with the mean volumetric radius, the effective gravity at the equator would be 9.7888m/s², compared with the actual 9.7804m/s². That means the effect of the bulge is 25% that of rotation. If launches near the equator are economically worthwhile, a quarter of that difference would be significant for such applications.

The advantage that I was speaking of was not that gravity is weaker due to centrifugal force, but rather that a smaller distance needs to be traversed in phase space. Is this what you were referring to.

[j1j2j3]

As a result, the effect of both the centrifugal force and the bulge is to decrease local gravity.

Anyway from what I remember the net gravity at the equator was a bit less than at the poles.

I think we are saying the same thing.

Though my wording was a bit off being drunk but...