I'm trying to make a soda can roll on its own down a level hallway and someone gave me this explanation on a possible way to do it, but I'm having trouble understanding how to execute it. Can someone explain it in different words? "One complicated mechanical way is to put a flywheel inside, on bearings, and with a brake, and a coupling of some sort. If you temporarily connect the flywheel to a motor and get it spinning, set the can on the surface, then turn on the brake, the can will take off. Or you can get it spinning with a crank and some gears. Or a spring. with the spring, you don't need to get the flywheel spinning beforehand, the wound up spring will transfer it's energy to the flywheel and make it spin, and make the can rotate in the opposite direction." I'm not allowed to use a motor (or anything battery powered) so I'd have to go with the spring method.