## Earth's Centrifugal Force vs. Gravity

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keeperofdakeys
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### Earth's Centrifugal Force vs. Gravity

I was wondering whether the centrifugal force from the earth spinning would decrease the amount of gravity we experience, compared to if the earth is not spinning. Although the significance may be quite small.

SlyReaper
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### Re: Earth's Centrifugal Force vs. Gravity

It does have an effect but it's negligible compared to the gravitational force.

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Josephine
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### Re: Earth's Centrifugal Force vs. Gravity

On that note, it would be possible to have very low gravity at a planet's surface by spinning it really fast.
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### Re: Earth's Centrifugal Force vs. Gravity

Closer to the equator or higher altitude = reduced effective gravity. It's nowhere near enough to notice in everyday life, but it is one of the reasons why NASA built their big launch facility at Cape Canaveral; it's relatively near the equator.
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keeperofdakeys
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### Re: Earth's Centrifugal Force vs. Gravity

So we make a hypothetical earth and spin it so fast that gravity is negated, and then some. (Assuming that the planet is strong enough to not fall apart from the negative gravity). Would we experience near-normal gravity at the poles? and would something endlessly rise from centrifugal force and come back from the gravity (since it is not touching the planet, and not experiencing centrifugal force; assuming no atmosphere)?

Edit:
Although now I think about it, wouldn't you have gravity pulling in a direction away from the normal when not located near the equator. Such that, if the planet were spinning fast enough, we would have many people who could be The Man Who Fell Sideways?
Last edited by keeperofdakeys on Wed Jul 21, 2010 2:05 pm UTC, edited 2 times in total.

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### Re: Earth's Centrifugal Force vs. Gravity

The main advantages of equatorial launch are the almost .5km/s initial velocity you get, and the fact that it makes achieving a geostationary orbit easier.

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### Re: Earth's Centrifugal Force vs. Gravity

There's an interesting bit here about what would happen to the oceans if the earth stood still. It's more masturbation with ArcView than a serious attempt to figure anything out, but it does talk a bit about gravity and centrifugal force.
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SlyReaper
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### Re: Earth's Centrifugal Force vs. Gravity

Velifer wrote:There's an interesting bit here about what would happen to the oceans if the earth stood still. It's more masturbation with ArcView than a serious attempt to figure anything out, but it does talk a bit about gravity and centrifugal force.

That article seems to be assuming that the Earth itself is rigid. Surely the ground at the equator would sink slightly too, being no longer supported by the centrifugal force?

Also, if the Earth stopped spinning, we wouldn't HAVE oceans as we know them anyway. The sun-facing side would evaporate away into the atmosphere, and the dark side would freeze solid. There would also be terrifyingly powerful storms all along the day-night divide.

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WHSTech
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### Re: Earth's Centrifugal Force vs. Gravity

Plasma Man wrote:Closer to the equator or higher altitude = reduced effective gravity. It's nowhere near enough to notice in everyday life, but it is one of the reasons why NASA built their big launch facility at Cape Canaveral; it's relatively near the equator.

Cape Canaveral is closer to the equator for a reason, but it's not because of diminished gravitational force. It's there because the closer you are to the equator (and spinning faster), the easier it is to launch stuff into orbit because of the added rotation from the ground.

Vyn
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### Re: Earth's Centrifugal Force vs. Gravity

What's the formula you'd have to use to determine the gravitational flux from the force at the equator? Since it's roughly ~1000mph, what speed would you have to start spinning Earth at to get say half-gravity effect or no gravity effect?

And lastly... isn't it centripetal force? Or did centrifugal force get added to dictionary like "ain't" did through attrition?
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SlyReaper
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### Re: Earth's Centrifugal Force vs. Gravity

Vyn wrote:What's the formula you'd have to use to determine the gravitational flux from the force at the equator? Since it's roughly ~1000mph, what speed would you have to start spinning Earth at to get say half-gravity effect or no gravity effect?

And lastly... isn't it centripetal force? Or did centrifugal force get added to dictionary like "ain't" did through attrition?

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### Re: Earth's Centrifugal Force vs. Gravity

Plasma Man wrote:Closer to the equator or higher altitude = reduced effective gravity. It's nowhere near enough to notice in everyday life, but it is one of the reasons why NASA built their big launch facility at Cape Canaveral; it's relatively near the equator.
Yeah...no. Lower gravity has nothing to do with that. Greatly increased eastward velocity, on the other hand, has everything to do with it.
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### Re: Earth's Centrifugal Force vs. Gravity

Vyn wrote:What's the formula you'd have to use to determine the gravitational flux from the force at the equator? Since it's roughly ~1000mph, what speed would you have to start spinning Earth at to get say half-gravity effect or no gravity effect?

And lastly... isn't it centripetal force? Or did centrifugal force get added to dictionary like "ain't" did through attrition?

F = mv^2/r is the formula for centripetal force; so the total apparent force is zero when v^2/r = g; at that velocity, any object on the surface is also in orbit. For half-gravity, v^2/r = g/2.

Centripetal force is the force 'toward the center' that curves the path of a moving body, which makes sense in a fixed reference frame. In a rotating reference frame, there is an apparent centrifugal force term (see the comic slyreaper quoted, above, and I love that it's available to make the point) proportional to mr(w^2).
(I haven't got the hang of writing TeX math, so I can't get a proper omega, but if someone would like to help me out, I'll edit it...)
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### Re: Earth's Centrifugal Force vs. Gravity

SlyReaper wrote:That article seems to be assuming that the Earth itself is rigid. Surely the ground at the equator would sink slightly too, being no longer supported by the centrifugal force?
It's also no longer got all that water on it. Isostatic uplift would likely be more than enough to counter the loss of the bulge in the short term.
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