The experimental apparatus consists of a plane adjustable to various angles of incline. A ball can be rolled down the plane; it bounds when it hits a springboard at the base. The problem is to find the relationship between the height of the point from which the ball is released and the length of its bound. Naturally the subject will not be able to calculate the parabolic form of the curve the ball describes, but he will be able to discover that its length varies only as a function of the height of the release-point (learning to exclude the effects of the mass or weight of the ball). In part, the solution of the problem depends on the way in which the factors are presented.