Comprises a spring loaded steel rod mounted in two brackets on a metal base. Provided with one solid steel sphere and one steel sphere with a hole to slide it into the rod. Spring compressed by the handle which can be locked into two different positions corresponding to two potential energy levels. Once spring is compressed, the sphere with the hole slides onto one end of the rod, while other is placed in a small recess on the opposite side of the base. On releasing the handle, the potential energy of the compressed spring imparts horizontal velocity to the solid sphere while the other sphere simply falls vertically. Falling of both the spheres on the ground implies that vertical and horizontal velocities are independent.