Demonstrates on of the most interesting and informative of all basic physics experiments - finding the fastest path between two points in the same vertical plane but not in a vertical line. Johan Bernoulli solved the problem by poving that the path of lieast time ("brachistochrone") is an inverted cycloid. The apparatus demonstrates that fact; it consists of three grooved boards, side by side hte surfaces of which are formed in a) a straight line b) an arc of a circle and c) a cycloid. Three steel balls are released simultaneously from the tops of the three boards. The ball rolling down the cycloid arrives at the bottom first, followed by the ball rolling down the arc of a circle while the ball rolling down the straight line arrives last!