Because the rolling time down a cycloid ramp is constant for all release points, this pair of ramps allows you to vary the velocities and impact angle of two colliding balls without changing the collision point. In use, the ramps are positioned at the edge of a table, and the collision point is projected onto the floor with a plumb line. A sheet of paper with carbon paper on top of it (not included) is taped to the floor to mark the landing positions of the balls after collision. The distances of the balls' impact points from the projected collision point are proportional to their velocities, allowing a full analysis of the collision event. Set includes 2 cycloid ramps and stands, 2 half-inch steel balls, 2 three-quarter-inch steel balls, a plumb line, and an instruction sheet.