When I'm riding my bicycle, I can be barely moving forward--say 10 cm/sec.--and I'm able to maintain my balance easily. But if I'm completely stopped, I cannot do it. Of course some people can maintain their balance on a unicycle when they're not moving, but I don't have balancing skills which are too unusual. So, what's going on here? What difference does that little bit of velocity make? I don't think it can be the gyroscopic properties of the turning wheels, because they're barely spinning.