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How Do Objects Hang in Outer Space?

  1. May 9, 2014 #1
    How Do Objects "Hang" in Outer Space?

    I'm wondering how it is that things in outer space just "float" and don't "fall" down or collide into each other? In the ocean, for example, if you put objects with weight into the water, they will generally sink or I guess they can float too. But how is it that objects in space don't seem to "fall" and just stay suspended in the air? Or am I missing something?
     
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  3. May 9, 2014 #2
    Because of the gravitational field around the objects, they (massive objects) can even collide in the space.
     
  4. May 9, 2014 #3

    Drakkith

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    Objects in space are not "floating". They are moving around at different velocities relative to different objects. For example, satellites in geosynchronous orbit are not moving relative to the Earth's surface, but are moving very quickly relative to the Sun.
     
  5. May 10, 2014 #4

    Bandersnatch

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    It's like with a falling elevator. If you're inside, you, all the other passengers, and any other object you may have with you, will float in air. Of course, from another point of view, the whole thing is falling very fast towards the collective doom of the passengers.

    In orbit, all objects are constantly falling towards Earth(or whatever they orbit). But since they're also moving sideways at huge speeds(kilometres per second), they keep missing the ground.

    A space station is just like the elevator. Everything inside, and everything in the same orbit more generally, falls at the same rate, so from that point of view everything appears to float.

    The condition of weightlessness in space is called "free fall" for a good reason.
     
  6. May 10, 2014 #5

    Simon Bridge

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    generally: if the camera is falling at the same speed as the object, it will look like it's floating: you've seen this in sky-diver footage on TV. It is just the same in orbit. More generally, things will "float" if the camera (or you or whatever) is moving at the same speed as the thing, accelerating at the same rate etc.

    That's all there is to it.

    However, I was interested in what your question tells me about your current understanding... taking your points in order:

    1. "outer space" is a big place - did you have any particular place in mind? The exact answer depends on the location.

    2. objects in space do "fall down", and they do "collide into each other".

    3. objects in space are not normally "in air" ... this is why astronauts need space-suits.

    4. It is fair to say that you've "missed something":
    You have noticed that falling only happen in special circumstances - i.e. close to the surface of the Earth.
    But you have asked the question assuming that "things fall" is a universal law of some kind and that the "things floating" involves some special circumstances.

    In fact, it is the other way around: do you know why things fall in the first place?
    I think this will be key to your understanding.
     
    Last edited: May 10, 2014
  7. May 10, 2014 #6
    Tendency of the body to continue in its state of rest or of uniform motion unless and until an external force acts upon it is called inertia.

    In space where there is no force acting on the object, the body continues to be in the same state, either rest or uniform motion.
     
  8. May 10, 2014 #7

    sophiecentaur

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    But there's nowhere where this applies. Gravitational attraction never 'gives up'. the inverse square law doesn't have an end point. It's just that the forces can be very very small, so the effects can take millions of years to show themselves.
     
  9. May 10, 2014 #8

    A.T.

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    Where is "down" in space?

    They do that.
     
  10. May 10, 2014 #9

    Simon Bridge

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    @kyphysics: any of this help?
     
  11. May 11, 2014 #10
    Hi, Bandersnatch

    This is very interesting and an awesome explanation. The notion of everything falling at the same rate like inside of a falling elevator makes sense. Also, the idea of of things moving due to gravitational effects makes sense...

    My only question is why objects move to begin with? Why wasn't everything still from the beginning?

    (p.s. Is the weightless thing really called "free fall" as an actual science term?) :smile:

    Hmmm. When you say there is no force acting on an object in space, what do you mean by that? How can there be NO force whatsoever? That's very odd sounding.
     
  12. May 11, 2014 #11
    Oh, very helpful. Although I don't understand everything at the moment, some of the analogies were very helpful. I'm still trying to conceptualize some things and asked some questions about those areas. I greatly appreciate it guys!

    I never took physics in high school. My senior year, I went with Oceanography, because I knew my math skills were sub-par and was scared to take it. I just am very curious about the topic now that I'm finally in college (well, that's community college, but still college!).

    Still a bit scared to take an actual physics course, but I hope to do so one day.

    Amazing post. Thanks very much. You are correct in that I assumed all of those things!

    To start with, I understand your camera analogy, but I'm not sure how that would apply to space. If space is the camera (I'm assuming that's what you meant), then how is it that space itself is moving? And suppose space was moving somehow, are you saying it's coincidentally moving at the same rate as all the other objects in it? This was a bit weird for me to grasp.

    As far as a particular location in space, I think I was just asking about space as a whole. I suppose I meant all of space. I was thinking of it in terms of something like the ocean. In my original post, I asked why don't things behave they way they do like objects in water. Most objects will just sink to the bottom of the water in a body of water. So I was curious why objects in space - as a whole - don't "sink" in the same way. So I think I meant just all of space.

    As for objects in space not being in "air," what exactly is there in space then? Doesn't there have to be air all around?

    Lastly, if what you're saying is correct about objects "floating" being the norm and not the exception, then that's very interesting!

    Thanks so much for your help!! You guys have been awesome!
     
  13. May 11, 2014 #12
    As hinted by other posters, "sinking" and "falling down" are meaningful only when you can define "down". When you are standing on the surface of planet Earth, your definition of "down" is "toward the centre of the Earth". You could say, well, a definition is nice to have, but how about a determination? The determination (on the surface of planet Earth) is very simple: you just release an object and it just falls "down", which determines where "down" is. The question is then why does everything fall down (on the surface of planet Earth)? The answer is "gravity". Gravity is attraction between any two massive objects, and it so happens that it is always in the direction between the centres of two objects. The notion of "centre" may become complicated if an object has some weird shape, but, thankfully, the Earth is very nearly a perfect ball so it is easy to understand where its centre is.

    Now, let's go up (which is the opposite of down) in space. Up in the space, there are many objects, many of which are more massive than the Earth (all stars are more massive, and there are things that are more massive than stars). Where is your "down" now? Is it toward the centre of the nearest star? What is there are two stars nearby? Or if all the stars are far away? You can try your "Earthly" method to determine where "down" is: release an object. But in this case, as explained by others, it will just not go anywhere from you, it will be floating next to you, rather like it would in a falling elevator. You and the object are in free fall, and there is no "down"!
     
  14. May 11, 2014 #13
    Read my post once again, "In space where there is no force acting on the object, the body continues to be in the same state, either rest or uniform motion".

    I didn't say there is no force acting on an object in space.

    I said, in space where there is no force acting on the object, the body continues to be in state of rest or uniform motion. Actually such space doesn't exist, so there will be force acting on the object in space (as sophiecentaur noted).

    Don't type the post in hurry:grumpy:
     
  15. May 11, 2014 #14

    Simon Bridge

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    One of the cornerstones of science is that when Nature does not match the assumptions about Nature, we discard the assumptions. We don't try to explain away the bits of Nature that don't fit.
    But it is easy to get sucked into trying to find explanations that fit the expectations.

    It's not an analogy - I mean literally the POV of whatever or whoever is watching the scene is the camera. Sometimes it is a literal camera.

    No. That is not what I meant.
    I mean that whoever or whatever is watching the floating thing in space must be moving at the same speed and direction as the thing being watched. If they were not, then the thing being watched would not be floating, it would be moving away.

    You've seen footage of skydivers right - the ones where one of the skydivers has a camera attached to his helmet? Notice how all the other skydivers appear to be floating about in the air? (If you've never noticed that, you can find lots of examples on YouTube.)
    The same principle applies everywhere.

    You've already resonated with the falling lift situation - when you are in the lift going down, you may notice that you get a bit lighter for a bit, but other than that you don't notice the movement. Everything is moving at the same speed.

    If the lift were just dropping instead of being lowered by cables, you'd be able to let go of a ball and watch it hang in the air in front of you ... because the ball, the lift, and you, are all falling at the same rate, which is because gravity makes everything fall at the same rate.

    You are correct in that this is called "free fall": the situation where you are falling and nothing holds you up at all ... one of the side effects of free-fall is "weightlessness".

    A body of water like the ocean is on the surface of a planet like the Earth ... objects, like balls, close to the Earth, when released, will move towards the Earth from the point of view of a camera/observer that is sitting on the surface of the Earth.
    If the camera was sitting on the object, then the Earth falls towards the object.

    This is the effect of the law of gravity - objects attract each other, and fall towards each other. What you see depends on where you are standing.

    In water, you will notice that some things float.
    To someone sitting, say, in a boat, an object dropped over the side may float or sink depending on how big it is compared to it's weight - the water pushes it up, and gravity pulls it down.

    This is called "the principle of Archimedes".

    You should google for that ans "law of gravity" as well.

    Then why do astronauts wear spacesuits to go into space if there is air all around for them to breathe?

    There is only air in a very thin layer around the Earth.
    Up very high the air thins out into nothing. Space is that nothingness.
    It's usually called a vacuum.

    It's more that "floating" is not a good word to describe what is going on.

    It carries the idea of being supported, like when things float in water, and that is not what is happening here.

    It's looking to me like you need to start with Newton's Laws of Motion, and then tackle Newton's Law of Universal Gravitation. Just to get your thinking sorted out. There are courses online.
     
    Last edited: May 11, 2014
  16. May 11, 2014 #15
    While I very much agree with the other points you made, this is weaker. Even here on the Earth people wear protective suits. So just the presence of a protective suit on an astronaut does not per se mean it is because of a lack of air.

    In fact, we know that there are other things up there that require protection from, such as the intense radiation coming from the Sun and the relative coldness of the surroundings. So at least a thermal insulation is required regardless of the absence of air.
     
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