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Thread: GRAVITY!!!!

  1. #1 GRAVITY!!!! 
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    So, I'm in Gr. 12 University Physics with no prerequistes and I'm finding some difficulty with an assignment relating to gravity. I need to do well in this class as I have been offered a scholarship but missing the Gr.11 U Physics has made doing well in this class extremely difficult.

    Anyways, the assignment requires that I consider a society where gravity does not exist. I have to figure out what would be the resultant and I need to know how I can compensate for it in order to sustain life. Here is what I got/questions:
    -I figure that without gravity there is a possibility of bones decalcifying as a result of there being no weight bearing exercises. So, I thought that setting up spring systems such as the bow flex could possibly defer it. Is there any way I can express this in terms of physics?
    - How would there be air resistance without gravity? If true, then if I jump I would never land as there is no opposing force; thus, Newtons First Law applies.
    - Is it true that everything would be slow motion? If so, why in terms of physics would that be? Would a bullet be slower? I don't think it would change the momentum because momentum is a result of mass and velocity; thus the bullet would produce the same injuires. If no, then would everything be like free falling? If jumped up and then push off on say a ceiling would the force required to land be too overwhelming, potentially life threatening.

    Anyways, I don't expect anyone to do calculations. All I am asking for is confirmation on some of my predictions and pointing in the right direction so i can make calculations. Thanks.


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  3. #2  
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    Slow motion? - definitely not, astronauts appear to move slow because they are trained to move that way, the faster you push yourself off, the more energy you use and the more you will need to stop. Air resistance will be there because the air is, moving through a medium (in this case gas) requires you to displace the gas, that is resistance. If you jump you will continue until another force opposes you. there is no reason why a bullet dhould be slower, (though if in the space station I wouldn't put it to the test..). the force you use to push yourself off the ceiling would be the same as that required to stop you once you got back to the 'floor' since your legs are around 7 times more muscular than your arms, no problem.

    Jump of a wall 2 feet high (here on earth) no problem, now do a hand stand and 'jump' landing with your hands, it'll almost certainly break both ulna and radii bones.


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  4. #3  
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    Thanks! Is there any way I can do calculations to show how sensitive motion would be with there being no gravity.

    Also, why would it be the same force needed to stop me when someone would reach the floor?
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  5. #4  
    Red
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    emm pretty much jst take the downwards force of it out of any equation everything else especialyy horizontal motion would remain constant although by that i mean force applied horizontally behind something as in a bullet i would think that horizontal motion over a parallel surface such as walking would be made dificult as the vertical componant would probably life u off
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  6. #5  
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    The need to move slowly and with very calculated force just adds to the problem you mentioned earlier: Muscles and bones are not used the say way, or to the same extent, as under gravity.

    Actually, some of your ideas sound pretty good, but to answer the question "how to compensate" for a lack of gravity, you should also refer to "artificial gravity". I think that would be a straight-forward and obvious suggestion, as seen in many sci-fi movies: Use centrifugal or other types of acceleration to simulate gravity and circumvent any biological problems.
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    Quote Originally Posted by ender7x77
    Thanks! Is there any way I can do calculations to show how sensitive motion would be with there being no gravity.
    As Red said, just remove the normal acceleration due to gravity, i.e., 981cm/s2, from any calculation that would otherwise include it.

    Quote Originally Posted by and also
    Also, why would it be the same force needed to stop me when someone would reach the floor?
    That's a question of momentum, which is the product of mass x velocity. Momentum is conserved in the absence of external forces, such as gravity and air resistance. So, the force necessary to stop your motion when you hit the floor is the same as that used to push you from the ceiling. Of course, if you didn't actually stop, but rebounded, then you would still have some kinetic energy until something else stopped you, (like the ceiling )
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    Quote Originally Posted by redewenur
    until something else stopped you, (like the ceiling )
    or maybe the bullet....
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  9. #8  
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    the force required to stop me ( i know it wouldn't exaclty equal but i figure it be close with there being no gravity). I'm trying to prove this in order to make-up a science fiction based game for the creativity component of the assigment. So, far I have determined that the velocity would obviously be constant and i have been trying to play around with magnitudes and impulses but I cannot figure out how I would calculate the force necessary to push myself off the wall. Anyways, any help would be very appreciated.
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  10. #9  
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    Any force will get you off the floor, since there is no subtracting force of gravity, the pushing-off force can be extremely small, and you'll still move away from the floor. The speed of the body will be relative to the force of the body pushing off.

    Note that I haven't looked this up or something but just by thinking. But I seriously dought that it is wrong.

    Now, life in an universe without gravity is impossible, because mass cannot form planets.
    The infinite heat of the big bang will cool down rapidly and 90% of all matter will have circa the same temperature.

    Thus making the universe to a big clump of matter, rapidly dwindling energy and a disappearing heat source.
    This makes the universe an even more hostile for life forms, since the matter is incapable of forming bodies (with the acceptation that it can stick to each other)

    But I believe there is still a way. When the big bang occurs and the absence of gravity lets the matter scatter around the universe, it could be that some matter cooled off to form huge crystals of some sort that are hollow, and can let a light source illuminate the crystal. Then there are some other weird singularities that come to it.
    The crystal must be filled with water (just that the hole crystal body is covered from the inside), the life medium in our universe.
    Then the crystal has to turn, faster than the earth to create the artificial gravity.

    The only problem you have now is that you don’t have a sun, which isn’t very good because of the fact that it is our life source (medium=water; source=sun).
    In the middle of the crystal, something would have to be there to illuminate.

    Well it sounds mad but that’s the chances of life in a universe without gravity.
    I haven't come to fight my word, but to find the truth.
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  11. #10  
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    forget about bones dicalcifying. how bout buildiing a giant glass bubble around the earth to keep all that air in. hmm and the water in the sea, and the dirt on the ground. and how about a really long rope to attach to the sun you can keep spinning around the thing. (or have they given you set question to answer?)
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  12. #11  
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    Hmm...yes a giant transparent globe would do, orbiting the sun. Plants could be grown for food in floating clumps of soil. Water could be encased in metal spheres. Instead of streets, metal 'kick-off' panels could be arranged around the inside of the globe so you would have something to use to propell yourself from here to there, using the same panels to stop your motion. They would have to be connected to each other and anchored to the globe to hold them in position. A well designed pattern of these panels would enable the inhabitants to travel anywhere they like inside the globe. You'd carry a map and each panel would be marked, like street signs.

    There would be no gravity at the inner surface of the globe, its gravity created by the globe would be concentrated at it's center. If the globe were made of a strong but very light-weight material, some nano-structure, for instance, it would not create much gravity in itself.

    Just some of my thoughts on the subject
    "Where are you going?" "I go where it is changeless." "How can you go where it is changeless?" "My going is no change."
    http://www.youtube.com/user/starmoun...d?feature=mhee
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