[@Dark Light] that's not 100% accurate if we're going from an electrical source you only need enough energy to equal the length of the rods also the current loops into the other railing creating a magnetic field that looping field charged the object and sends it flying forward with force equal to that current pushed through it. You can actually do it with a car battery if you have something powering it. The circuit created from said interaction (the principle behind lorentz force) is pretty simple to make. The projectile shorts the two railings and jumps forward. I only know this because I tested it out granted I needed to tape several magnets down under the two rails its also worth mentioning it only works with DC power