If you fallow conservation of energy ( Kinetic+ potential ) then you can see why it's impossible to have perpetual motion, Also it contradict with Entropy increase with time.
Follow this;
First law of thermodynamics - Conservation of energy. Energy can be transformed from one form to another, but it can't be created or destroyed. "You cannot win (that is, you cannot get something for nothing, because matter and energy are conserved)."
Second law of thermodynamics - Entropy. Systems always flow to a state of disorder. "You cannot break even (you cannot return to the same energy state, because there is always an increase in disorder; entropy always increases)."