HOW FAST CAN IT GO?
As the rubber band unwinds, it tries to turn the popsicle stick and the pencil. The friction between the popsicle stick and the can is too great to move the stick. The pencil can move because the bead and plastic disk have less friction between them. However, when the pencil tries to turn, it pushes on the floor (which pushes back) and so the only way the rubber band can unwind is to roll the can forward. As the can rolls, the potential energy that is stored in the wound rubber band is transformed into motion (kinetic energy) and heat. The can will roll if the energy stored in the wound rubber band produces a force great enough to overcome the force of friction between the bead and the disk and between the can and the floor.