This seems kind of weird, but is there really no such thing as gravity in

  1. [SOLVED] This seems kind of weird, but...is there really no such thing as gravity in

    Hi, I was just wondering about this because....you see how there's supposed to be no gravity in space, but i sort of think there is because of the movement found within our glaxay and our entire solar system. uhh...it's kind of hard to explain, but everyone knows about the Corneleous Effect found on Earth. Ugh...i can't spell it but it's the movement of ocean currents and it shows that ocean currents above the equator move clockwise while the currents move counter clockwise below the equator. These ocean currents are caused by gravity, right?
    Well....how exactly is our milky way galaxy moving in a spiral and our planets circling around the Sun? The reason why this is happening to our solar system is simple. As we all know planets tend to orbit around those who are larger because they have a stronger magnetic pull also known as gravity. (this can include stars, right?) well, as we know, our Sun is the largest Star, therefore, the planets would orbit around it, causing the circular motion.

    But why do galaxies move that way? But if there is gravity in space, where is it coming from?
     
  2. jcsd
  3. dav2008

    dav2008 624
    Gold Member

    There is no point in space with 0 gravity.

    There is always the force of gravity no matter where you go, and only at a distance of infinity from an object is its gravitational pull equal to 0...

    The reason that astronauts are weightless in orbit is because they are constantly falling towards earth but the earth falls away under them at the same rate so they just move in a circle around the earth....
     
  4. LURCH

    LURCH 2,514
    Science Advisor

    Wow, you ask a lot of questions NP (we like that here!).

    Your initial conclusion is correct; there is indeed gravity in space. And yes, that is what makes things orbit one another. If the difference in mass between two things is great, the more massive thing will stay in one place (almost), while the lighter object orbit around it. Two objects of nearly equal mass will orbit some point between them. So the moon's goal around the planets, and the planets orbit around the (much heavier) stars. The stars in the galaxy, being of roughly equal mass to one another, just orbit a central point.

    As dav was referring to, astronauts only appear weightless in space because they are going around the earth fast enough so that the outward "centrifugal" force (which is really just a form of inertia) is equal to the downward pull of gravity. The two forces back against one another so that the total result is "0", but that's not exactly the same as saying that gravity = "0".

    As for the Coreolus Effect (pretty sure I didn't spell it right, either), that's not so much a gravity thing. It's a little complicated, but suffice to say that gravity only plays a minor role.
     
  5. chroot

    chroot 10,426
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    Re: This seems kind of weird, but...is there really no such thing as gravity in space?

    As has been explained, there certainly is gravity in space.
    The Coriolis force is essentially just a result of winds (or water currents) moving over a planet that is spinning beneath it. It makes freely moving objects make curved paths with respect to the surface of the earth. It isn't really a force at all -- it's akin to other ficticious forces: you can choose a coordinate system in a way to remove the Coriolis force.
    The galaxy isn't moving in a spiral; it has a spiral shape, and things on the periphery are orbiting the center of mass.
    While I understand what you're attempting to say, the word 'magnetic' is not appropriate at all here. Gravity and electromagnetism are two completely unrelated phenomena (at least until we have a Theory of Everything <smirk>).
    The Sun is absolutely not the largest star. In fact, the Sun a puny, average, unimportant star -- except to us humans. What you're grappling at is the concept of 'superposition.' In other words, say you have one mass by itself. You can calculute the force vector experienced by a test mass at any point you like. You can thus describe a 'gravitational field' by expressing what the force vector is at all points in space. You can then add a second, identical mass to the system. The second mass's gravitational influence is simply stacked on top of the first ones -- the two fields can be simply added. The resulting field is just the simple sum of the two fields created by each mass -- the resulting field is the superposition of the two independent fields.
    Einstein's theory of general relativity explains gravitation as an effect of curved spacetime. In essence, mass curves space -- and space then tells mass how to move.

    - Warren
     
  6. Yes! (i love this subject) Globular clusters, as they are called, specify a group of binary stars that do more than just orbiting. When they orbit each other, they get caught up in the gravitational pull of nearby stars (and it should be noted the stars are very ((relatively speaking)) close to each other) and the star that is pulled into another binary system collides with one of the stars in the binary system. [sigh] Its very complex.
    Binary systems are two stars that orbit each other. One small star orbits another big star (like the Alpha Centauri system).
    As chroot said, our sun is really not the largest star. In fact, its at a stage where its really young, and therefore small. The biggest a star can get is, at the age of 20 million, the super red giant. When our good ol' star gets to that age, then it'll get so big, that it'll wipe out the inner planets (mercury to mars). So, in conclusion, our star is fortunately small.
     
  7. chroot

    chroot 10,426
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    No offense MV, but do us a favor: if you don't know something, please either 1) do not post it or 2) preface it with something like "I'm not sure, but I think..."
    I don't know what you're talking about -- perhaps you're discussing contact binaries -- but it's not globulars.
    No. Both stars, no matter what size, orbit their common center of mass.
    Our Sun is not "young." It's about 50% of the way through its life, about 4.6 billion years old. Stars are not necessarily smaller when younger either.
    Stars reach the red supergiant phase at different times, depending upon their mass. Unless you're talking a star with at least 100 times the mass of the sun, it won't be a red supergiant in tens of millions of years.

    - Warren
     
  8. enigma

    enigma 1,815
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  9. Re: Re: This seems kind of weird, but...is there really no such thing as gravity in space?

    I don't believe he wanted his post torn apart and corrected on unneccesary points, such as magnetism NOT being gravity, he wasn't speaking of it as a force, but simply as an attraction.

    Anyways, galaxies don't move in a circular orbit, as has been said, but towards other objects, such as galaxy clusters or any other galaxy larger than itself.

    Planet's rotate around other stars, and the sun is the largest star in our system, I think this is what you meant, because the ripple they cause in space is sufficient to hold the planet's in it.

    How could this be taken any way BUT offensive. And he DID know what he was talking about. NP was just referencing our system of planets, and very often planets are in globular clusters.
     
  10. chroot

    chroot 10,426
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    Re: Re: Re: This seems kind of weird, but...is there really no such thing as gravity in space?

    Science is rigorous -- it's important to correct any misunderstandings (or perhaps just poor wording) immediately.
    In most cases, galaxies orbit the center of mass of the local group. They don't necessarily move "towards" anything, but follow standard Keplerian orbits about the center of mass like any other body.
    Actually, a globular cluster would be the worst possible place to look for planets.

    - Warren
     
  11. :smile: Thanks for answering my questions!! I really appreciate it, but uhh.... I sort of have trouble understanding some of the terms u use so if it's not too much trouble can u define them too? ^_^

    I'm sort of confused too, because i don't see why our Sun isn't the largest star. But I must disagree with u on one point MV. hehe, sorry but our Sun isn't a young star because it if was it's color would be bright blue or white. As stars age their colors tend to change into a deep red, that's how u'll know that it's a oollddd star, right?

    ^_^ and kyle_soule is right. I was just wondering bout the positions and movement of our planets and why they do, but since i'm not even in highschool yet my intentions might be a bit vague. hehe sorry.

    o!! i just got another thought!!! Aren't there black holes in our universe? What happens to the matter than gets absorbed by them? Does this create a time flux within our universe ~because there's no time in space~? So do u guys think that they're the reason why time bends?

    rarr! the more answers i get the more questions i come up with, haha. But now that i can finally get answers and opinions from people I can't help asking! after all..i'm only 11 years old
     
  12. By The Way...

    I'm a girl not a boy!!! rarr! hehehe, and it's ok kyle_soule because when Warren tells me what's wrong with my thoughts or theories I learn more. That's why I'm on here to share them, hehe:wink:
     
  13. russ_watters

    Staff: Mentor

    The sun is a relatively small star. Thats just the way it is. "Why" really isn't a relevant question. Also, age isn't the only thing that affects color - mass affects color. And since our sun is relatively small, it doesn't burn as hot, and therefore doesn't glow blue. Our sun is estimated to be halfway through its 10 billion year life.
     
  14. chroot

    chroot 10,426
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    Our Sun only looks so big because we're so close to it. We're only 93 million miles from it -- but the next closest star is almost 24 trillion miles away!
    This is, in very general terms, correct. Stars expand and cool as they reach the end of their main sequence lives. As a result, old stars are usually large and red. However, this doesn't mean that all young stars are small and white!

    It all depends on the mass of the star, as a matter of fact. Very massive stars are very hot and thus white or blue in color. These stars also burn out very quickly -- so if you see a blue-white star, you know it can't be very old. On the other hand, a low-mass star might appear red or orange even when it's young.

    So to recap: 1) All old stars are red, but not all red stars are old. 2) All blue-white stars are young, but not all young stars are blue-white.
    When a black hole absorbs some matter, it just gets a little larger -- there's nothing spooky going on with time or gravity or anything. There are, however, some spooky things that happen to the information content of the matter that fell in. For example, if you throw a Shakespeare play into a fire, the information is not really lost -- it's just spread out into the ashes and smoke. You could in principle look at all the atoms of ash and smoke and see what the book said -- though it would, of course, be very difficult. On the other hand, if you throw the Shakespeare play into a black hole, the information in the book is irretreivably lost forever, even in principle. It would take a lot more talking to really help you understand the consequences of this, though. Don't worry though, nothing funny happens to time when something falls in a black hole.

    - Warren
     
  15. "The Coriolis force is essentially just a result of winds (or water currents) moving over a planet that is spinning beneath it. "

    It's not, it is an inherent effect of 3-d circular motion. It shows up in a transformation from rectangular to polar coordinates.
     
  16. This is not necessarily true. A white dwarf can be really old, and how its name indicates, is white (in fact the Sun will be a white dwarf in 5 billion years, after reaching the stage of red giant)
    If you consider a black dwarf like a star, is an exception too
     
  17. chroot

    chroot 10,426
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    That's certainly true, and thank you for pointing it out. I was talking about (though I did not specify) only about active stars still burning fuel.

    - Warren
     
  18. Does this mean that very old stars are white? Then why are old stars red? And how can our Sun when it reaches the stage of a RED giant be a WHITE dwarf? rarrr astronomy is confusing, but I still like it ^_^

    uhhh....this sounds weird but..what did everything he said up there mean? it sounds complicated though. hehe, either than that i have no clue of what he meant when he said "It shows up in a transformation from rectangular to polar coordinates", someone explain it to me. please??
     
  19. chroot

    chroot 10,426
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    Stars generally go through the following phases:

    Protostar: radiates mostly in the infrared; fusion has not begun

    Main sequence: adult life for a star -- massive stars are hotter and blue-white; less massive stars are cooler and redder

    Red giant: reaching the end of the useful hydrogen fuel -- these stars are larger and cooler and redder than when on the main sequence

    At this point, the evolution of small mass and large mass stars differ.

    End of life for small stars: white dwarf: the core of the dead star, no longer producing any energy. The rest of the star's mass is thrown off into a planetary nebula, leaving the hot white core in the center.

    End of life for moderate mass stars: neutron star: a very dense state of matter. These stars are associated with pulsars.

    End of life for very massive stars: black holes.

    - Warren
     
  20. Oooo! I remember what a planetary nebula is! That was the picture you showed me of a ring of colors! I still have it.
    But where do the colors come from in this planetary neubla? I know that colors form in rainbows because of water vapors that infract the beams of white light (did i use that word correctly?). But there's no water in space so where do the colors come from in a planetary nebula?
     
  21. chroot

    chroot 10,426
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    (NB for others reading this thread, she's talking about M57, the Ring Nebula. A picture is available here: http://antwrp.gsfc.nasa.gov/apod/ap000716.html)

    Anyway, the colors are a result of gas being heated to different temperatures. The gas is hottest near the center, and coolest on the outside edge. Hot gas creates higher frequencies of thermally emitted light.

    - Warren
     
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