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Thread: Big Rock turned into small Bullet

  1. #1 Big Rock turned into small Bullet 
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    Imaging this. We've got a row of rocks , aligned on a hill. Their masses are in the following order: 100 kg, 50 kg, 25 kg, 12.5 kg, 6.25 kg ... and say we come to something below 1 kg.

    Now if we push the 100 kg rock upon the other rocks, the kinetic energy should completely transmitted to the small ones, cause the smallest to act like a bullet, right?


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  3. #2  
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    No. The collisions between rocks will not be perfectly elastic, and even if they were, it would not work as you think. If a large mass collides with a smaller mass in an elastic collision, it retains most of its momentum and kinetic energy. It is only in collisions of equal masses that the momentum is all transferred. Momentum and energy both have to be conserved in an elastic collision.


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    Forum Bachelors Degree dmwyant's Avatar
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    So that is why a Newton's cradle uses the same size spheres?
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    Comet Dust Collector Moderator
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    Yes, that's why
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    Forum Bachelors Degree dmwyant's Avatar
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    A related question Is there a limit to the size of spheres one could use other than production. If you had multiple planets set up in a Newton's cradle would the energy transfer work the same provided they had identical mass and composition
    Not all who wander are lost... Some of us just misplaced our destination.

    I would rather be a superb meteor, every atom of me in magnificent glow, than a sleepy and permanent planet. The proper function of a man is to live, not to exist.
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    Anti-Crank AlexG's Avatar
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    A related question Is there a limit to the size of spheres one could use other than production.
    On mythbusters, they tried to scale up the Newton's cradle to use wrecking ball sized spheres, but they were unsuccessful in getting the elastic collision that they needed.
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  8. #7  
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    It works with planets. The slingshot effect sometimes used to accelerate space craft is basically an elastic collision, though they don't physically collide.
    Gravity assist - Wikipedia, the free encyclopedia
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    Forum Professor Zwolver's Avatar
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    How can you calculate what part of energy is transferred from 1 object to another if comparing size and mass..

    Lets say.. 2 objects, both with a radius of 10cm, one is 1kg, one is 10kg.. The 10kg ball will hit the 1kg ball, what speed will both balls have after this..

    We know the heavy ball can never move faster then the light ball, as it can not pass it. But it can not transfer all it's speed to the light ball, so it'll still move..

    lets say the heavy ball had an initial speed of 10m/s and it has no friction in moving, of bumping.

    What would happen?
    Growing up, i marveled at star-trek's science, and ignored the perfect society. Now, i try to ignore their science, and marvel at the society.

    Imagine, being able to create matter out of thin air, and not coming up with using drones for boarding hostile ships. Or using drones to defend your own ship. Heck, using drones to block energy attacks, counterattack or for surveillance. Unless, of course, they are nano-machines in your blood, which is a billion times more complex..
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    The relevant equations to calculate final velocities in a 1-dimensional elastic collision are here.
    Elastic collision - Wikipedia, the free encyclopedia

    Plugging the numbers into the forumula from the wikipedia page, I get
    KE of m1 before collision = 500
    v1 after collision = 8.18
    v2 after collision = 18.18
    KE of m1 after collision ~334.7
    KE of M2 after collision ~165.3
    Last edited by Harold14370; July 17th, 2012 at 12:05 PM.
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