Can any one explain how the kinetic energy of this magnetic marble gauss rifle works?

  1. Check this site address out: http://scitoys/scitoys/scitoys/magnets/gauss.html

    It is a neat little science project site, and I found this project the most interesting (except for the non-elecricity requiring radio) on their site. How it tells you it works(shortened): You take a ruler and place 4 cubed magnets and place 2 metal marbles in between each and only 1 at the ends. Then you let go of the first one and it rolls toward the magnet w/ a kinetic energy of 1. Then the KE is transfered through the magnet to the second ball with a KE of 1, and then that ball hits the 3rd one with a KE of 1. By the time they hit the second magnet they have a kinetic energy of 2 and it keeps on building up untill the last one is hit and the marble goes flying across the room from trmendous amounts of KE.

    What I want to know is (in more detail) how the KE is carried and what the resulting amount of kinetic energy is by the time it hits the last marble. Please help me work out the math. I think I understand how when the 2nd ball hits the third with a kinetic energy of 1 it transfers it to the 3rd ball. But do they both then move toward the 2nd magnet with the power of 2 KE since their sum of their KE equals two? Or is that no correct? Would it be 1 instead? And if so then how does it build up the KE? Help please.
  2. jcsd
  3. Any one?
  4. Janus

    Janus 2,524
    Staff Emeritus
    Science Advisor
    Gold Member

    Okay, First off, I'd think it it be easier to think of it in terms of momentum than KE, but to each his own.

    When you let go of the first marble (A), it is pulled towards the first magnet (1), accelerating as it does so.

    On the other side of magnet 1 are two marbles(B&C). The momentum of marble A is transfered through magnet 1 and marble B to marble C. This is enough to break the magnetic grip magnet 1 has on C and still have some momentum left over.

    (Marble C will not have quite the same KE as A at this point because some of it was used to break away from magnet 1 . One purpose of marble B is the increase the distance between marble C and magnet 1 and reduce the amount of energy needed for this. )

    Marble C is attracted to magnet 2 so it accelerates towards it. (this is the other purpose of marble B, so that marble C starts out far enough away from magnet 1 such that it gains more momentum falling towards magnet 2 than it loses pulling away from magnet 1 )

    Marble C will strike magnet 2 with the combined momemtum that it got from Marble A plus the momentum gained by acceleration due to its attraction to magnet 2. It tranfers this momentum to marble E through magnet 2 and marble D, Which in turn gains additonal momentum by accelerating towards magnet 3 , etc.

    In such a way, each marble in the sequence has more than the previous unitl you get to the last marble.
  5. Thank you for explaining that.:smile:

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