Does Rotational Speed Affect Gravitation Pull?

[Frankieanime158]

Question. (bear in mind I'm not a rocket scientist, so I may sound stupid).

But, I believe the density of a planet effects whether or not it can maintain an atmosphere. If it doesn't have enough mass, particles escape. 

But what if one wanted to put an atmosphere on a planet that doesn't have one (say, the moon). Considering it's too light to really hold much, would increasing it's rotational speed enable it to maintain a stronger atmosphere? 

And than, if that rotation is sped up, would it also increase the planets gravitational pull of stuff around it?

I guess that's 2 questions.

1. Maintain an atmosphere

2. Increase gravitational pull

 

My own mind tells me if you dumped a bunch of gas in it, it wouldn't escape (assuming speed up enough). But, it wouldn't pull things around it more. Asides from what added weight would come from throwing gas into it.

[Canada EH]

Wrong, it needs mass to hold things to itself, rotational speed would fling it out.

[Ertman]

My guess is no to both more gravity and being able to hold onto an atmosphere.

 

I am not a physicist, not even an amateur one, but I would think that adding rotation would have no impact on the planetoids gravity itself, but it would counteract the force of gravity the least at the poles and the most at the equator, and the force of the rotation would only make it more difficult to hold onto an atmosphere.

 

Waiting to be corrected...

[KarathKasun]

Centrifugal forces are what increases with rotation.  These forces would reduce the effect of gravity.

[Frankieanime158]

Ahh, okay, thanks guys I definitely see what you mean, thanks for the information.

[mr moose]

4 hours ago, KarathKasun said:

Centrifugal forces are what increases with rotation.  These forces would reduce the effect of gravity.

Then why do people not feel/be heavier when they stand at the north or south pole?  Apart from not getting dizzy that is.

 

 

[asus killer]

the moon has gravity, it's what causes tides on earth

the moon has an atmosphere, just not equivalent to earth's (https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html)

 

i had no idea about rotation causing gravity, googling it it appears not, it's mass like said previously that causes it, but plays a role in it. This seams to explain it (http://www.askamathematician.com/2013/01/q-if-the-world-were-to-stop-spinning-would-the-people-and-everything-on-it-be-considered-lighter-or-heavier-would-any-change-take-place-and-does-centrifugal-force-have-an-effect-on-gravity/) and kind of using @mr moose argument

 

edit: a follow up question: to what point would earth's gravity allow the moon to have a earth like lawyered atmosphere?

[Ertman]

3 hours ago, mr moose said:

Then why do people not feel/be heavier when they stand at the north or south pole?  Apart from not getting dizzy that is.

 

 

People are measurably heavier at the North Pole, the amount of reduced force excerted on the body due to the rotation is so small that you wouldn’t likely feel it as the weight change is less than 0.5% if I recall this correctly. 

 

Also I think your dizziness question is mostly answered by relative velocity, where standing on the earth, the speed is constant for the observer so you don’t feel the rotation of the earth. 

 

2 hours ago, asus killer said:

the moon has gravity, it's what causes tides on earth

the moon has an atmosphere, just not equivalent to earth's (https://www.nasa.gov/mission_pages/LADEE/news/lunar-atmosphere.html)

 

i had no idea about rotation causing gravity, googling it it appears not, it's mass like said previously that causes it, but plays a role in it. This seams to explain it (http://www.askamathematician.com/2013/01/q-if-the-world-were-to-stop-spinning-would-the-people-and-everything-on-it-be-considered-lighter-or-heavier-would-any-change-take-place-and-does-centrifugal-force-have-an-effect-on-gravity/) and kind of using @mr moose argument

 

edit: a follow up question: to what point would earth's gravity allow the moon to have a earth like lawyered atmosphere?

The moon’s current mass would never allow for it to have an earth like atmosphere by simply changing the earth gravity. However, in theory you could create an earth like atmospheric pressure temporarily by transplanting an atmosphere there, probably through the use of comets. This would dissipate over a couple thousand years because of the low gravity of the moon.

 

 

 

remember I am not authority on any of this.

[dalekphalm]

9 hours ago, mr moose said:

Then why do people not feel/be heavier when they stand at the north or south pole?  Apart from not getting dizzy that is.

 

 

Relative differences.

 

If you're up on a mountain top, gravity is less, but do you notice it? Probably not.

 

The centrifugal force is tiny compared to the gravity exerted by the mass of the earth.

[mr moose]

I still think we should be dizzy and fall off... 

 

[InertiaSelling]

2 hours ago, dalekphalm said:

The centrifugal force is tiny compared to the gravity exerted by the mass of the earth.

The earth is flat. If centrifugal force counteracted the effects of gravity, people on the edges would be ejected into space. Therefore centrifugal force isn't real. See, physics is simple.

[dalekphalm]

1 hour ago, mr moose said:

I still think we should be dizzy and fall off... 

 

That's... not how it works. People get dizzy because they are spinning and their visible surroundings aren't.

3 minutes ago, InertiaSelling said:

The earth is flat. If centrifugal force counteracted the effects of gravity, people on the edges would be ejected into space. Therefore centrifugal force isn't real. See, physics is simple.

This would be funny if there weren't people who actually believed what you just wrote.

[mr moose]

1 hour ago, dalekphalm said:

That's... not how it works. People get dizzy because they are spinning and their visible surroundings aren't.

 

Sorry, I was just being facetious.  

 

1 hour ago, InertiaSelling said:

The earth is flat. If centrifugal force counteracted the effects of gravity, people on the edges would be ejected into space. Therefore centrifugal force isn't real. See, physics is simple.

 

Actually, if the earth was flat the mass of the earth would still counteract centrifugal force.  So as we get closer to the rim the buildings would have to be built leaning out and walking along respectively flat ground would feel like walking up hill.    Effectively it would feel and be built as if the Rim was a steep slope.

 

[Bhav]

eARth is fLAt AnD dOeS nOT ROTatE!

[Godlygamer23]

18 hours ago, KarathKasun said:

Centrifugal forces are what increases with rotation.  These forces would reduce the effect of gravity.

Remember that centrifugal forces don't actually exist, and it's just the object wanting to continue traveling on the path it's already on.

[ATFink]

16 hours ago, mr moose said:

Then why do people not feel/be heavier when they stand at the north or south pole?  Apart from not getting dizzy that is.

 

About the getting dizzy part:

The period of rotation of the Earth is 24 hours (technically 23 hours, 59 minutes, 0.86 seconds with some error since I'm not counting the absence of a leap year after every 49th leap year... [365*4*24*60*60]/{[(365*4)+1]*24*60*60} and multiplied that number by 24*60*60, convert to hours:minutes:seconds and you get my presented number). That is such a long time there is no way a rotation that slow could make you dizzy. That's why most people don't get dizzy on merry-go-rounds even though they literally spin several thousand times faster than the Earth does (from a perspective of angular velocity).

 

I don't know whether frame of reference when spinning aids in making people dizzy. You could test this by spinning quickly with your eyes open and closed and noting if there is a difference... I don't advise you do this in case you bash into something however. If this does have an effect then you shouldn't be as dizzy from Earth's rotation since everything around you spins with you, giving the effect of no apparent spin at all.

 

About centripetal forces:

Actually, there is an apparent change in weight. There is a very small effect of increased centripetal force counteracting our planet's gravitational force at the equator vs the poles. This means you feel lighter at the equator, but it's just so minute you won't notice. The reason it is small is the same reason you don't get dizzy when standing on Earth. It's our planet's very slow period of rotation that makes this effect unnoticeable. Assuming Earth's gravity is a constant of 9.81 m/(s^2) everywhere on Earth *(it isn't)* you can determine that if an accurate scale at one of the poles reported your weight to be exactly 100 lbs (45.359 kg) then that same scale at the equator would report your weight as 99.656 lbs (45.203 kg). Your day to day change in weight based on consumption, perspiration, and excretion is likely much more significant than your change in weight from the equator to one of the poles.

 

Here's the math (that most people probably don't care to see... thus it's hidden):

Spoiler

Notice, there is a VERY slight error (like, 0.1%) because I used gravity of 9.81 m/s^2 when in fact it is slightly different. I don't know the exact number and I'm not going to look it up. Floating point conversions in my calculator may have also played another slight role in error since there were orders of 10^-11 through orders of 10^24, sometimes squared or multiplied together at points.

 

To correct for this I divided the end equator weight by the end pole weight and multiplied this fraction by the original 100 lbs (45.350 kg) to find a more exact value. I did not show this step on the page I used, but it is applied to the end numbers that are circled. Anyways, here's the math:

 

* There actually are microgravitational effects near the surface of the Earth that do change the gravity experienced by the observer in some specific areas, but again, it's so slight you won't notice. This is outside the scope of discussing centripetal forces, so it's in a note down here.

Edited February 12, 2018 by ATFink
Explained actual length of a day, microgravity, and clarified an explanation.

[straight_stewie]

19 hours ago, Frankieanime158 said:

1. Maintain an atmosphere

2. Increase gravitational pull

 

I think I know where you got that idea: The artificial gravity spacecraft you got the rotational gravity idea from is a little different (and would actually work). The only caveat is, it only makes it feel like there's more gravity (really it's just centripetal force) on the INSIDE of the object, while things attached to the outside of the object will experience negative gravity in relation to the object.

If that makes any sense.

[mr moose]

44 minutes ago, ATFink said:

sniparoony

Thanks.