Horizontal Cast and Collision Tester (1889) Here is a unique way to study horizontal and vertical motion, conservation of energy, and momentum. A track mounted to a vertical board directs one or two carts, casting them into a free fall. A brush projecting from the back side of the carts, marks the path of the cart as it falls. Weights can be added to the carts to study the effects of increased mass on momentum. Qty :