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so my younger brother is making project for school in physics and making a basic rail gun, where the projectile is launched, using rubber band, between two aluminum rails (13.8 cm in length and 0.56cm apart), which are hooked up to 5x 470uF caps charged at about 325V. The problem we are facing is how to calculate forces on the projectile (a rod l=2.57cm, r=0.275cm) and how to get the exit velocity when we roughly know the force with which the rubber band is pushing at the start (We want to know theoretical velocity but at the same time not theoretical in perfect environment, but in our universe :) ).

Everything would be mostly okay if there weren't a huge spark with every shot, that, I think, dissipates most of the energy and we have no clue how to account for that + what effect it leaves on projectile speed.

If somebody could help, or at least point to right resources, that would be much appreciated, our search results haven't helped us to get that damn explosion to behave on paper :)

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  • $\begingroup$ Re, "...how to get the exit velocity" You could construct a ballistic pendulum. It doesn't have to be much more sophisticated than a lump of putty with a known mass, hanging from a length of string, right in front of where the projectile exits from your gun. Point a video camera at it from one side, and use a sheet of graph-paper behind it to provide scale. $\endgroup$
    – Solomon Slow
    Commented Jan 16, 2020 at 21:39
  • $\begingroup$ @SolomonSlow We are trying to get theoretical velocity as the real exit velocity can be measured at school using light gates $\endgroup$
    – Puupuls
    Commented Jan 16, 2020 at 21:45

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