Question on Gravity at the equator. more or less?

Discussion in 'Astronomy, Exobiology, & Cosmology' started by nebel, Oct 13, 2018.

  1. RainbowSingularity Valued Senior Member

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    7,447
    i am wondering...
    how do you get a sphere to spin in all directions at once ?
    you cant...
    i gues you could have layers of spinning fluid.
    a centre then a layer around it spinning the opposing direction... then so on and so on...
    i wonder what would happen to gravity.

    there doesnt appear to be any examples of planets/moons/stars not spinning.
    this is a problem because it means the sphere must be spinning.

    what is the gravity of a planet that stops spinning ?
     
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  3. nebel

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    2,469
    Because there is a linear relationship between size and surface gravity of homogeneous masses.
    Double the size of a symmetrical spheroid, and you double the surface Gravity[potential]!, and the reverse is true too. so:
    Why would the reduction in radius at the poles lead to an increase in gravity measurements there?
    Perhaps the mass below is not even , with a well defined, doubly massive core, changing the gravity gradient from the linear ideal? so:
    By stating the radius alone would lead to an increase in Polar Gravity seems questionable.
    Decreased radius should lead to decreased gravity, right down to the zero value with near oblateness, a zero value that is always there, at the center of every mass, oblate or not.
    Show me the graph of increasing and then decreasing gravity of a gradually flattening obloid and I will show you a convinced audience.
     
    Last edited: Oct 16, 2018
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  5. nebel

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    well, we have very slowly rotating bodies in the solar system: Venus, for example, and
    the Sun and the Moon both waltz together at ~ 28 days per turn.
    The energy of that movement seems to be part and parcel of the gravity equations and measurements. or? anyway,
    In the ratio of Polar and Equatorial gravity, the rotational component is of very little influence.
     
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  7. RainbowSingularity Valued Senior Member

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    is the over all gravitational field of the planet a collective energy of the total over all matter(in the planet) and its rotation specifically added/connected to the orbital velocity(the outter fast spinning mass parts) as a total amount of gravitational field at the poles ?
     
  8. nebel

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    2,469
    It would increase gravity only to the extend that mass increases with velocity or acceleration, and since the rotational velocities are so small compared to "c", we can safely ignore that, when comparing Polar (stationary)*** and Equatorial gravity.
    *** There is the difference in velocities discussed in the "Jupiters velocities cancel", now in the "pseudo" section. and
    Yeah, looking from the Sun, relativistically, you weigh also less at noon on the equator than at the Poles, because you move momentarily slower there (except onVenus)
     
    Last edited: Oct 16, 2018
  9. origin Heading towards oblivion Valued Senior Member

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    11,888
    Post reported for pseudo science in the science section.
     
  10. nebel

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    2,469
    The above, objected-to reply #25 , had nothing to do with the proposition and question of the OP. Here again a valid query can be sidelined toward the pit, because off-topic postings appear; pity. Origin, please you could please help instead to show with a graph how a formulation can go from increasing gravity at the poles to bringing it finally to zero, based on the increased oblateness.
    what I meant to say is that the introduction of extraneous material, that might have been done in good faith (everyone has his own hobbyhorse) should not be reason to relegate a valid query based on approved data to the "questionable" sections.
    Then again Benefit of the doubt should be applied and see whether the "Alternative" criteria rather than "Pseudo" really apply.
    How can a question on real data ratios , (on this thread : gravity rising and falling with radius) be pseudo? another previous example:
    The Orbital versus Rotational velocities question?
     
    Last edited: Oct 16, 2018
  11. origin Heading towards oblivion Valued Senior Member

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    11,888
    In post 25 you made a obviously pseudoscience statement and presented it as factual. There is no place for that in the science section.
    It great to ask questions or make queries. The problem is you bringing in your pseudoscience crap into the science section. You know this but do it anyway, you must think you are above the rules of this forum.
    Why would I waste time on that? You have shown time and again that you ignore any information that does not fit into your preconceived notions. It is just a waste of time.
     
  12. nebel

    Messages:
    2,469
    well in general you should not! just ignore simpletons like nebel&co. but: your good hobby is to elevate the scientific standard of the forums. good. but we provide much needed entertainment, even insights, so please tolerate daring data dalliances. but
    finding and posting a graph, that explains a function that describes both rise and fall of a gravity value would be appreciates by all, as was your post #2 on "inside/outside gravity". and
    Post# 25 was a response to an off- topic question; only redirecting it into an esoteric domain. responding in kind. but kindly, without "crappy" comments. so:
    Can you help with that graph?
    My objection to your request is that
    Every theme should be judged on it's merits and not on wayward postings that ensue during the discussion.
     
    Last edited: Oct 16, 2018
  13. RainbowSingularity Valued Senior Member

    Messages:
    7,447
    venus was going directly between earth and the sun a day or 2 ago.
    i was (almost)expecting maybe a few more earth quakes or such like.
     
  14. nebel

    Messages:
    2,469
    Your information is false. see quote from Wikipedia below.

    "the last transit of Venus was on 5 and 6 June 2012, and was the last Venus transit of the 21st century; the prior transit took place on 8 June 2004. The previous pair of transits were in December 1874 and December 1882. The next transits of Venus will take place on 10–11 December 2117" !!!!
    The mass of Venus is only .0003% of the Sun, and we are not even discussing equator/ polar gravity gravity lessened by rotation or external pull. but
    I will pass on another transit prediction: The Moon will transit the Sun 2000 days from now. aka eclipse
     
    Last edited: Oct 17, 2018
  15. NotEinstein Valued Senior Member

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    1,986
    But the gravitational potential isn't relevant here; we were talking about the gravitational force. So I'm not sure why you'd bring up this irrelevancy?

    All of this is irrelevant: we're not scaling the object, we're deforming it. So a linear relation between the size and surface gravity of homogeneous masses is neither here nor there.

    Also, as you yourself pointed out, we're not talking about homogeneous masses either.

    Do the math, and you'll find out.

    What "linear ideal"?

    When you say "gravity gradient", do you mean the gradient in the gravitational field, potential, force, of something else?

    What's that "well-defined, doubly massive core" you are talking about?

    Nobody is stating that: the radius doesn't lead to an increase in polar gravitational... Erm, potential? Field? Force?

    Potential? Field? Force?

    Sure, reducing the volume of an object without deforming it (i.e. scaling it down, or "shrinking" it), reduces the mass, and thus the strength of its gravitational field, and thus the strength of the gravitational forces on its surface.

    But we're not talking about that; we're talking about deforming a sphere.

    If you do the math, I'll make a graph out of it. Deal?

    Looking through this thread, I don't think I need to look any further for that...

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  16. NotEinstein Valued Senior Member

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    1,986
    Wait, what do Venus transitions have to do with anything?

    *looks at Origin's post*

    Ooh... Oh right, I almost forgot this is nebel we're talking to.

    That's quite true; I'm laughing right now.

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    But you know what's not funny? Stealing other people's work. I haven't forgotten that, you know...
     
  17. nebel

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    2,469
    The math proving the increase of gravity I have seen, all assume that the body is an ideal homogeneous entity, but for simplicity's sake, the OP used the example of the Earth which is not. So we are talking about both.
    A gravitational potential becomes a force when it acts on a body, so I use the simple term gravity to mean either. put yourself in the spot and kind of feel it
    The Earth's core, ~ double the specific weight of the mantle. with a distinct demarkation surface that can be gravitationally detected.
    you are misreading again, I said increasing oblateness, which is not changing the mass, or the volume, but the ratio of the dimension, NE nit picking , and going wrong again!
    Make it a first for you, do something creative for a change, do both, (Do not steal somebody else's work)
    You are the real sorry example of libel (trying to steal someones good reputation) on these forums; --- Because scrolling through it all, you will find oodles of unattributed fair usage usage of images. so: shame on you to accuse all of us to be thieves. but
    Your naysaying is good, clarifies points, so:
    Deforming, without changing volume or mass, first increases Gravity at the axis of an abloid, spheroid, but then-- decreases it to zero. graphs please., the supposed math is already "out there somewhere".
    thank you! nebel.
    . .
     
    Last edited: Oct 17, 2018
  18. origin Heading towards oblivion Valued Senior Member

    Messages:
    11,888
    Gravitational potential and gravitational force are are not the same thing. Gravitational force at the center of a uniform sphere is 0, gravitational potential is not. Using one term to define both potential and force is incorrect. It is no wonder that your attempts to explain your thoughts on gravity are so confused.
     
  19. NotEinstein Valued Senior Member

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    1,986
    So "for simplicity's sake" you're picking the more complicated setting? Right, makes sense.

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    Ah well, doesn't matter; both have been addressed.

    And I see you've chosen to ignore the other things I pointed out. Can you please go back and address those too?

    I see you don't understand the relation between potential and force. May I suggest you look up the difference, and realize how bad it is to mix the two up, especially when dealing with their gradients? And how terribly wrong your description here is?

    What do you mean by that?

    Ah, OK.

    Yes, I misinterpreted what you meant, but I don't think I'm solely to blame. Next time, when you don't want to talk about changing sizes, please don't talk about doubling sizes a few sentences earlier, and then suddenly jump subject without announcing that.

    Actually, just changing the oblateness parameter of a shape typically does change its volume; this is for example true for oblate spheroids, which is the shape we are talking about.

    Exactly: keep the major axis constant (which is what's done by default in mathematics), and change "the ratio of the dimension". The total volume changes.

    I understand you meant something along the lines of: "change the ratio of the dimensions, while keeping the total volume constant", but due to your lack of knowledge about mathematical language, you didn't know you had to add that second part. Well, now you know. Glad I could help you learn something today!

    A nitpick that was quite necessary, because the context of the original statement was confusing.

    About "going wrong": How about you address the issues you've ignored by your selective quoting? And how about you stop leading me in the wrong direction, if not "going wrong" is so important to you?

    As I said earlier: if this is a challenge, I'm not interested. I may be creative, but I'm not a lazy-person-enabler.

    Feel free to contact the moderation staff if you think I've committed libel. It's against the forum rules, you know!

    I'm not interested in stealing your reputation.
    And you have neglected to recollect the part where you were lying about the copyright status of the picture in question, and then lied about the wishes of the creator, all the while claiming to want to give the creator the credit he deserved. You didn't even know who the creator was: I had to look that up. (Welp, looks like I'm a lazy-person-enabler after all!

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    )

    No, I am definitely not interested in stealing your reputation. You can keep it.

    If you think I'm (falsely?) accusing all the members of these forums to be thieves, feel free to contact the moderation staff.

    Yep, so that "NE nit picking" was useful after all! I'm glad you agree that it was warranted.

    Here's another nitpick: are you talking about a homogenous oblate spheroid, or not? And I'm glad you are now specifying to keep the volume constant; I'm happy to have corrected you!

    And so is the graph.

    And why don't you make it a first for you, do something creative for a change, do both, (Do not steal somebody else's work)?

    Glad I could help!
     
  20. NotEinstein Valued Senior Member

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    1,986
    Hey Origin, stop "NE nit picking", you thief!

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  21. nebel

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    2,469
    Please explain that here. In my thought experiments I assumed that there is a gravitational field, that has strength. Gravity in the sense that it originates from an entity. The average reader might not see the distinctions either. and :
    where is, or can you construct a graph that shows the near 0 gravity at the poles of a really flat spheroid, as it rises to the levels we see for the earth, and falls to parity on the surface of that uniform sphere you mentioned above. thank you. and
    There has to be a second point of equal gravity on that graph of ratios of polar & equatorial diameters, where it passes the parity value again on the way down. Without raising your ire about pseudo science again,
    would it be surprising if that ratio approached 1:1.6 ? ( assuming that the original proposition of greater polar gravity causation is correct, and fibonacci was not a Pseudo scientist)

    PS: It occurred to me that the question raised in the OP is really a sub-set of the "most gravity in or out" thread, and you should be up to the task to furnish a comparative post#2. with zero at the center of the x and y axes.
     
    Last edited: Oct 17, 2018
  22. nebel

    Messages:
    2,469
    I think we can agree that a uniform globe has equal gravity (insert the correct term) at both poles and equator, because of equal radii. That parity changes as the polar radius shrinks and gravity there becomes stronger (asserted solely) through the interplay of distance to mass (total mass does not change). but,
    As the oblateness, the ratios of radii becomes more extreme, it finally will come to 0, so then: there has to be parity like in a sphere somewhere at some ratio again. so where is that?. Parity twice, at the start and on the way down. what do the equations show, if they are valid and are asserted to be on so many sites,
    saying the smaller radius causes rise in gravity.
     
    Last edited: Oct 17, 2018
  23. origin Heading towards oblivion Valued Senior Member

    Messages:
    11,888
    I do not want to do your work since you have historically ignored it or distorted it. You can do this.
    The force of gravity at the center of a uniform sphere is zero, I think we agree on that. Look up the definition or gravitational potential, not gravitational potential energy. You should be able to see they are different things.
    No, a flattened sphere or a very large thin sheet of matter will never give you 0 gravity. Here is a classic physics problem that is used in gravitational and electric fields. Imagine an infinite plane composed of matter that has a constant density and thickness. If you are located at any height above that plane will there be gravity? How would the gravity change if you moved around the plain at a constant height?
    Why does there have to be a second point of equal gravity (I assume you mean the acceleration due to gravity is the same at the pole as the equator).
    I would be very surprised if when a sphere was flattened there would come a point where the acceleration from gravity at the pole was the same as the equator. Why would this fictional point have a ratio of 1 : 1.6; because it is a cool ratio? 22/7 is a cool number why not that number? Or 4, like the points of a compass....
     

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