Earth's Centrifugal Force vs. Gravity

For the discussion of the sciences. Physics problems, chemistry equations, biology weirdness, it all goes here.

Moderators: gmalivuk, Prelates, Moderators General

Earth's Centrifugal Force vs. Gravity

Postby keeperofdakeys » Wed Jul 21, 2010 7:39 am UTC

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.
GENERATION 2+i: The first time you see this, copy it into your sig on any forum. Divide by zero, and then add i to the generation.
Image
User avatar
keeperofdakeys
 
Posts: 658
Joined: Wed Oct 01, 2008 6:04 am UTC
Location: Adelaide Hills, Australia

Re: Earth's Centrifugal Force vs. Gravity

Postby SlyReaper » Wed Jul 21, 2010 7:46 am UTC

It does have an effect but it's negligible compared to the gravitational force.
Image
What would Baron Harkonnen do?
User avatar
SlyReaper
inflatable
 
Posts: 7780
Joined: Mon Dec 31, 2007 11:09 pm UTC
Location: Bristol, Old Blighty

Re: Earth's Centrifugal Force vs. Gravity

Postby Josephine » Wed Jul 21, 2010 7:58 am UTC

On that note, it would be possible to have very low gravity at a planet's surface by spinning it really fast.
Belial wrote:Listen, what I'm saying is that he committed a felony with a zoo animal.
User avatar
Josephine
 
Posts: 2142
Joined: Wed Apr 08, 2009 5:53 am UTC

Re: Earth's Centrifugal Force vs. Gravity

Postby Plasma Man » Wed Jul 21, 2010 8:29 am UTC

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.
Please note that despite the lovely avatar Sungura gave me, I am not a medical doctor.

Possibly my proudest moment on the fora.
User avatar
Plasma Man
 
Posts: 2029
Joined: Tue Jan 15, 2008 9:27 am UTC
Location: Northampton, Northampton, Northampton middle England.

Re: Earth's Centrifugal Force vs. Gravity

Postby keeperofdakeys » Wed Jul 21, 2010 8:42 am UTC

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.
GENERATION 2+i: The first time you see this, copy it into your sig on any forum. Divide by zero, and then add i to the generation.
Image
User avatar
keeperofdakeys
 
Posts: 658
Joined: Wed Oct 01, 2008 6:04 am UTC
Location: Adelaide Hills, Australia

Re: Earth's Centrifugal Force vs. Gravity

Postby Fume Troll » Wed Jul 21, 2010 8:46 am UTC

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.
Fume Troll
 
Posts: 249
Joined: Wed Jan 13, 2010 8:06 am UTC
Location: Scotland / Norway mainly

Re: Earth's Centrifugal Force vs. Gravity

Postby Velifer » Wed Jul 21, 2010 12:10 pm UTC

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.
Time flies like an arrow, fruit flies have nothing to lose but their chains -Marx
User avatar
Velifer
 
Posts: 1133
Joined: Wed Dec 26, 2007 4:05 pm UTC
Location: 40ºN, 83ºW

Re: Earth's Centrifugal Force vs. Gravity

Postby SlyReaper » Wed Jul 21, 2010 1:51 pm UTC

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.
Image
What would Baron Harkonnen do?
User avatar
SlyReaper
inflatable
 
Posts: 7780
Joined: Mon Dec 31, 2007 11:09 pm UTC
Location: Bristol, Old Blighty

Re: Earth's Centrifugal Force vs. Gravity

Postby WHSTech » Wed Jul 21, 2010 1:56 pm UTC

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.
User avatar
WHSTech
 
Posts: 23
Joined: Sat Jul 10, 2010 1:21 pm UTC

Re: Earth's Centrifugal Force vs. Gravity

Postby Vyn » Wed Jul 21, 2010 3:24 pm UTC

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?
I am Jon Stewart with some Colbert cynicism, Thomas Edison's curiousity, wrapped around a hardcore gamer sprinkled very liberally with Deadpool, and finished off with an almost Poison Ivy-esque love/hate relationship with humanity, flourish.
User avatar
Vyn
 
Posts: 108
Joined: Wed Apr 28, 2010 3:48 pm UTC

Re: Earth's Centrifugal Force vs. Gravity

Postby SlyReaper » Wed Jul 21, 2010 3:47 pm UTC

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?


I can't believe I have to do this, but:

Image
Image
What would Baron Harkonnen do?
User avatar
SlyReaper
inflatable
 
Posts: 7780
Joined: Mon Dec 31, 2007 11:09 pm UTC
Location: Bristol, Old Blighty

Re: Earth's Centrifugal Force vs. Gravity

Postby gmalivuk » Wed Jul 21, 2010 3:57 pm UTC

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.
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(cis male/he/him/his)
User avatar
gmalivuk
A debonaire peeing style
 
Posts: 22304
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There

Re: Earth's Centrifugal Force vs. Gravity

Postby EricH » Wed Jul 21, 2010 4:03 pm UTC

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...)
Pseudomammal wrote:Biology is funny. Not "ha-ha" funny, "lowest bidder engineering" funny.
EricH
 
Posts: 258
Joined: Tue May 15, 2007 3:41 am UTC
Location: Maryland

Re: Earth's Centrifugal Force vs. Gravity

Postby Azrael001 » Wed Jul 21, 2010 4:09 pm UTC

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.
23111
User avatar
Azrael001
 
Posts: 2385
Joined: Sun Nov 11, 2007 5:15 am UTC
Location: The Land of Make Believe.


Return to Science

Who is online

Users browsing this forum: No registered users and 5 guests