Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Increasing propulsion(rockets)-newb

  1. Mar 3, 2009 #1
    Newb here with a question. correct me if I've got anything wrong(I'm assuming I've got quite a number of errors here, so be patient)
    I'm assuming that in a rocket, the energy release in the combustion chamber is directed 2 ways, up and down and the one that provides propulsion is the force acting upwards and the force released downwards is wasted.
    in rockets, I have observed that at least half of the total energy released during the
    explosion in the combustion chamber is wasted as exhaust fumes which does not contribute to the velocity of the rocket. It is quite obvious, that if this
    half of the force can be redirected upwards(meaning all the momentum at every direction is focused only one direction) then the
    velocity of the rocket can be increased by a hundred percent. Is it possible to reflect this force upwards to further increase the rockets velocity?

    There is also another theory that I'm still not sure about, but here goes. According to Newton's third law, if a force's opposite
    equal is reflected to the same direction, and another opposite force of the opposite force is produced during the reflection and is reflected by the
    same reflectant(thing which had reflected the first opposite force) and another opposite force is produced and reflected, an
    infinite amount of forces can be made. This could mean that one explosion is enough to send a rocket moving for an infinite period.
    I'm guessing that there are other laws which would restrict this principle from existing. Still, iis it plausible at all? All in all, both these theories are merely hypothesis and not true unless proven.
    Thx for any help at all. I'm just wondering.
  2. jcsd
  3. Mar 3, 2009 #2
    Disclaimer: I am not rocket scientist, so my opinion can be wrong too.

    By Newton's 3rd law, the downward force on the exhaust is equal to the upward force on the rocket. Since mechanical power is equal to F X v, the much faster exhaust will waste much more energy than that gained by the rocket. The efficiency of rocket propulsion is very low, much less than 1%. Energy efficiency is not the major concern for rocket design; it is the mass of the fuel. By the conservation of momentum, the total momentum of the exhaust is equal to the momentum gained by the rocket (ignoring drag and earth gravity). Since the ultimate velocity of the rocket is much faster than the exhaust, the required fuel is a thousand or so times as heavy as the payload.

    The exhaust, when leaving the rocket, is entirely downwards, giving the maximum possible upward force on the rocket. After leaving the rocket, the exhaust hits air below so that it spreads out. However, since the exhaust has left the rocket, reflecting it won't have any effect on the rocket.

    You can't create forces by simply reflecting. To reflect any object, you need an extra force to do so.
  4. Mar 4, 2009 #3
    I also know little about rocket science.
    But i find the subject interesting, as there appears to be much room for improvement.
  5. Mar 5, 2009 #4
    Its more than that, following formula of K.E the energy distribution to the gasses will higher as compared to what the rocket gets.

    We need a sort of mechanical component to do that job, actually you need such a thing that distributes the momentum of the gasses to a set of matter, but in the opposite direction and without distributing the momentum to the body itself (if it does distribute, it should be in the direction at which the rocket needs to be propelled.)

    We cant achieve 100%...I mean, at most it'll be like a diesel engine, i.e much of the energy will be dissipated in the form of heat...I think it will be 70% at most.


    How can you say that?...actually there're only 2 forces, since earth wont be there when the rocket takes off, you can ignore that.

    aaa...I've made a component to derive the normal reaction from the internal stress of a body, so that might do the job.

    Actually its a part of propulsion system that I'm developing.
  6. Mar 8, 2009 #5
    Wow, I didn't expect replies so encouraging(mostly) replies. As I have aforementioned, I'm a real newb, not very old too(considered inferior, a little) so thanks for you peoples corrections. Learnt a lot. Actually, I thought people would think that this idea is nonsensical but thanks for not thinking that way(I hope) Anyway, got another question.-im not really sure where this goes, so please point me in the right category if this is the wrong section(im really lost)
    1.What is the difference between force and impulsive force?-both have same unit and identical formula
    2.If an object which has an impulsive force, hits an object which is stationary and presumably not easy to move, like a wall, Will the wall also exert an equal opposite impulsive force on the object(normal reaction)? If so, then why is it that the force exerted by the wall cause the object to move in the opposite direction of its initial direction?-from my understanding, the object and the wall exert the same amount of impulsive force which should cancel each other out and the object will be stationary.(do correct me if im wrong, I think I am)
    Last note, dE_logics,do you mind if you explain the system that your developing? It seems awfully interesting, and I'd love to learn. If you don't mind, could you mail me at this address:
    imaginia1993@yahoo.com Thx.
    Btw, to all the repliers, thx too and God bless!
  7. Mar 9, 2009 #6
    Last edited: Mar 9, 2009
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook

Similar Discussions: Increasing propulsion(rockets)-newb
  1. Magnetic propulsion (Replies: 8)

  2. Rocket propulsion (Replies: 3)