Extreme pedantry
Great story, but I don't think it was a railgun that you built.

A railgun uses two parallel rails which are connected one to each side of a power source. A conductive projectile, on contacting the rails, completes the circuit. The resulting interaction between the opposing magnetic fields in the rails and the current induced field in the projectile accelerates the bullet out of the railgun at silly speed.

What you wonderfully irresponsible louts built was more likely a Gauss gun, which uses electromagnets to fire ferrous projectiles.

(Of course neither one can be powered by mains electricity unless you rectify it to DC, which you definitely did otherwise the ball bearing would have stuck at the first magnet.)

Still, definitely worth a click.
( Scrumper, Wed 18 Feb 2009, 11:20, 1 reply)

Ah yes!
It WAS a gauss gun! Now I remember (I am old) the big yellow-painted DC gizmo that the teacher plugged into the mains.

Still scary though!
(Captain Placid 24/7 ball gags, brownie mix and clown porn, Wed 18 Feb 2009, 11:32, closed)

Wicked
You are lucky for doing this at school! Great science lesson though, wasn't it? Electricity, magentism, Newton's laws and with your nice nylon uniform blazer probably a bit on materials as well. Well done sir.
( Scrumper, Wed 18 Feb 2009, 11:36, closed)