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Thread: propulsion method's?

  1. #1 propulsion method's? 
    Forum Ph.D.
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    i know this is a really .. really stupid question...

    but .. in space...how dose the shuttle gain speed? you know .. say it was going to mars*just as an example...* how would i get there?

    it uses fuel? right.. so what makes the craft ove? the heat? or gass produced? or both ?

    thank you ...*but if you don't answere..no thank you!


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  3. #2  
    Forum Junior superluminal's Avatar
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    Oh my. There's so much to do, so little time. You should google on "rocket propulsion" and get some extremely basic knoweledge before asking this kind of question.

    Anyway, chemical rockets generally use a fuel/propellant mix (i.e. the fuel is the propellant). The chemical reaction (say mixing hydrogen and oxygen) results in great heat. This gives the molecules more kinetic energy. The molecules (propellant) exit the engine and impart their thrust (F = ma) to the rocket. Basically the hot expanding gas pushes the rocket forward using the old "for every action there is an equal and opposite reaction" deal.

    A nuclear rocket would heat the propellant (hydrogen? Water? Whatever) in the core and expel it out the back. The heat source and the propellant are totally seperate.

    All you need for any rocket is hot stuff (hotter the better) efficiently directed out the back end. (that's what the bell thingy does on rocket engines. It makes maximum use of the kinetic energy of the expanding gas).


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  4. #3  
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    i kinda knew that, what im really getting at, could any heat soure work?
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  5. #4  
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    Get a skateboard and a bottle of coke. Shake up the coke, and place it on the skateboard. Then open the cap of the coke.

    The force of the gases going out the front pushes the skateboard in the other direction. This is not because the gases are pushing against the air but because they are pushing against the bottle, which in turn pushes against the skateboard. It would still work in a vacuum.

    That is how rockets work.

    In 1926, the New York Times expressed chortling scorn at Robert Goddard's ideas of sending rockets to fly in space, as they had the incorrect notion that reaction motors needed air (or something) to react against.
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  6. #5  
    Forum Isotope (In)Sanity's Avatar
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    If your getting at what does it push against. Hmm, I guess it's own exhaust ? Then again space is not really a vacuum as much as one thinks. I'm sure there is enough particles somewhere in space to push off of. If not the exhaust introduced would do the trick.

    How would one push off a wall when the wall doesn't exist
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  7. #6  
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    Thank you InSanity for perfectly muddying the waters I was trying to make clear for our young friend! No, there isn't enough stuff in space to push against. You move yourself forward by throwing mass away from yourself. That is how Action and Reaction works.



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  8. #7  
    Universal Mind John Galt's Avatar
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    Quote Originally Posted by goodgod3rd
    i kinda knew that, what im really getting at, could any heat soure work?
    It doesn't, strictly speaking, have to be hot. If you were an astronaut in space, attached to a large bag of tennis balls, you could move by throwing balls away from you. The velocity would be determined by the ratio of the mass of the balls thrown to the combined mass of astronaut and remaining balls, and the velocity with which you threw them.
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  9. #8  
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    k,

    what if somthing really hot was on the back of a rocket, would the heat work on its own?

    now that you've explain'd it.. it looks doubtfun
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