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The law of conservation of momentum is WRONG practically tried.

  1. Jul 21, 2009 #1
    I developed a propulsion system...a propulsion system which has no interactions from the environment...i.e the force in completely internal.

    The principle that I used was that when you propel a mass (suppose a ball) on a heavy body and make it hit the heavy body, the impulse that was given to the ball will be transfered to the heavy body. Though the momentum from the ball will be completely transfered, since the body is very heavy, the momentum will be more by virtue of mass...since K.E has an exponential square relationship with velocity, we can say that despite all the momentum getting transfered to the heavy body, most of the energy is still left...this is seen in the form of a recoil on the ball.

    Diagrammaticality -

    O--------------------------------------------------------------------------------------------------------->|
    Ball Propelled and made to collide the heavy body it rests on Wall

    Since the the ball is very much lighter than the body, and it possesses the momentum by virtue of velocity, the K.E in it will be much higher...and so we can say that most of the energy will go to the recoil of the ball.

    <----------------------------------O |
    Ball recoils after hitting the wall

    So now...after the collision, since the ball in moving in the opposite direction as before, and if we slowly make it retard (de-accelerate) on the body itself (for e.g using magnets attached on the body and making the ball out of iron), this time, all the K.E that the ball possesses will be given to the body...that means, a much higher velocity attained in the opposite (or desired) direction...and finally for the first time a propulsion without interaction from the surroundings.

    Magnet to stop the ball before it collides.
    ___
    <-------------------|___|-----------------------------O
    Ball moving in this direction on the heavy body


    In fact, since the ball is made to propel INSIDE the body, it will initially attain a velocity in the opposite direction, this will also aid the motion in the desired direction (although after collision, the body will again flip velocity).

    BUT this is not working :cry:...I mean, I tried it. So the laws are wrong...........it's clear. It should have been successful.

    Though the conditions were not ideal...I mean, I was using friction to stop the ball (on the body).........but it should have worked!!...I was using a ball of a few grams on a ~8KG body on water!!

    And was throwing the ball by hand.
     
    Last edited: Jul 21, 2009
  2. jcsd
  3. Jul 21, 2009 #2

    Doc Al

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    I'm having trouble making sense of your post. What exactly did you do and why do you think it violated momentum conservation?
     
  4. Jul 21, 2009 #3
    Is it clear now?

    What did you get till now?
     
  5. Jul 21, 2009 #4

    Doc Al

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    I see that you revised your original post, but it's still not clear. Again: What exactly did you do?
     
  6. Jul 21, 2009 #5
    For the conservation of momentum, no other force must do work on the interacting entities
     
  7. Jul 21, 2009 #6
    What exactly did you not understand?
     
  8. Jul 21, 2009 #7

    Doc Al

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    Rather than play guessing games, just answer the question: What did you do?

    You threw something at something else? What's this about a ball being propelled inside another body?
     
  9. Jul 21, 2009 #8
    Ok...exactly the law is not wrong, but it should have worked!...it's not working!!

    Any reasons...any flaw with the theory?
     
  10. Jul 21, 2009 #9
    What I think is that the recoil is not sufficient.

    The impulse that the ball delivered is more than what is should by the theory and ultimately the recoil is less...
     
  11. Jul 21, 2009 #10

    Doc Al

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    OK. The best I can determine is that you threw a ball against a wall and it bounced back? So what?
     
  12. Jul 21, 2009 #11
    If I'm reading this right, then the reason this won't work is the same reason you can't use fans mounted on a sailboat to create wind for the sails.
     
  13. Jul 21, 2009 #12
    That wall was attached to a heavy massive boat...and the ball had iron inside it AND it was lighter by many magnitudes than the boat.

    The ball should have recoiled after hitting the wall...its velocity of collision should have almost been equal to the recoil velocity, i.e very less energy would have been transfered to the boat, even though the complete momentum of the ball was delivered to the boat.

    What I've done is tried stopping the recoiling ball using a magnet...that way the COMPLETE energy of the ball will be transfered to the boat...i.e without a collision......so boat should have a net propulsion since the energy by the ball has completely been consumed to propel the boat in one direction.

    Ok, I'll again try and describe the question.
     
  14. Jul 21, 2009 #13
    No you did not read it right.

    After the air collides from the sail, it recoils...I'm using this recoil (with almost all its energy conserved...i.e very less goes to the boat...since its heavy).

    If you try and stop this recoiling air slowly using the boat itself, all K.E possessed by the air will be consumed to propel the boat in one direction..........no doubt there WILL be a propulsion!

    Notice there's a difference between collision and stopping something slowly...the later will not have a recoil.
     
  15. Jul 21, 2009 #14

    negitron

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    No, you've got a net momentum of exactly zero. The reason is that when you throw the ball forward, you give the boat a momentum of -p rearward. When you stop the ball, either with a wall or with a magnet, the force is transmitted back to the boat, imparting a momentum of +p for a net p of 0.
     
  16. Jul 21, 2009 #15

    Doc Al

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    You threw a ball against a boat that was against a wall? OK.
    Why do you think it should have recoiled?

    OK, so you have some mechanism for stopping the ball inside the boat. Assuming that the mechanism is contained within the boat, then I would expect that the energy and momentum of the ball would become part of the "boat+mechanism+ball" system. Certainly no reason to expect momentum not to be conserved. I still don't see why you deduce that momentum is not conserved.
     
  17. Jul 21, 2009 #16

    Doc Al

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    Or are you on the boat, throwing the ball from the boat against a wall? (Do you see why this is confusing?)
     
  18. Jul 21, 2009 #17
    Law of conservation of momentum + law of conservation of kinetic energy thing.


    If it its a heavy boat and the collision is elastic, it can't happen that it won't recoil.

    That mechanism is a magnet which stops the ball 'slowly' i.e a without a collision. That way, all the energy will transfered to the boat...nothing to the mechanism. If the magnet is a solenoid and its turned off after the ball stops...no energy will be left in this mechanism. All the energy would have been gone to the boat and it would have got propelled in one direction since all the K.E from the ball will be used to do so.

    But this is NOT happening practically...so I assume the law of conservation of momentum as wrong.
     
  19. Jul 21, 2009 #18
    Or law of conservation of energy as wrong.
     
  20. Jul 21, 2009 #19

    Doc Al

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    Why do you think the collision is elastic? (And for the nth time, you haven't clearly described, in simple terms, just what you did. Please describe what you did in plain English.)


    Again, no idea what you're talking about. What is this "mechanism"? Is it part of the boat? You toss a ball onto a boat and all of its KE becomes part of the "boat + ball" system. (Of course, much of that KE will become random internal energy.)

    :rolleyes:
     
  21. Jul 21, 2009 #20

    Hootenanny

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    Let me see if I can decipher your set up before we try an sort out your misunderstandings. You have a boat floating on the water. Attached to the boat is a vertical wall. You throw a ball against this wall.

    Is this correct?
     
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