Magnetism

A gauss gun fires projectiles by converting magnetic energy into kinetic energy.

Click on the video below to see a simple gauss gun toy in action.

Roll one ball into the magnet and a knock-on effect adds force until the projectile is shot into whatever direction it's pointed (hopefully not into your eye).

Is there any practical use for them apart from as entertaining videos?

The most often cited possible is as a weapon (just what the world needs). But gauss guns might also come in handy for propulsion in space.

Want to make your own gauss gun? Check out the instructions here.