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Finding the Velocity of a BB on a Magnetic Linear Accelerator

  1. Nov 14, 2013 #1
    As is in the title, I am looking for a better way to measure the velocity of a ball bearing (actually only looking for speed) that has been accelerated by a magnetic.

    If you don't know what a Magnetic Linear Accelerator is, then this link/video should help:

    I already have some success with a slow motion camera, but my Accelerator is around 9 feet long, so keeping the all of it in the frame is very tough while also keeping the distance markers in focus.

    Any ideas on what technology I could use?
    Last edited by a moderator: Sep 25, 2014
  2. jcsd
  3. Nov 14, 2013 #2

    jim mcnamara

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    Staff: Mentor

    Projectile velocities are usually measured with a chrongraph for ballistic data. Midway has one that works on sub-sonic projectiles for less than $US70. In the US: Gun shops that specialize in reloading supplies handle various kinds of chronographs.

    You can also google for 'how to build a chronograph'.
  4. Nov 14, 2013 #3
    Thanks. I was looking into that option.

    The only issue that I also want to measure the velocity of the BB while its still on the track.
  5. Nov 15, 2013 #4


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    Staff: Mentor

    Welcome to the PF.

    Depending on the geometry of the track for the BB, you may be able to use a closely-spaced pair of photointerrupter devices to measure the speed of the passing BB. You can use something as simple as a digital oscilloscope to capture the delta-time between the closely spaced interruptors (say 1cm apart), and calculate the speed from that. Or you could build a larger circuit that measures the speed at several places along the track, using pairs of photointerrupters at each location.

    Last edited by a moderator: Sep 25, 2014
  6. Nov 15, 2013 #5


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    Science Advisor

    An alternative would be with a pendulum. The BB embeds itself in the pendulum which swings up and pushes a marker that stays where it is pushed. Knowing the mass of the ball, pendulum and dimensions you can calculate the kinetic energy of the BB by measuring the potential energy of the pendulum with ball. Convert the height change of the pendulum to PE = KE of ball, then to BB velocity.
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