COLLISION IN TWO DIMENSIONS

For demonstrating the principle of conservation of momentum and showing that momentum is a vector quantity having direction as well as magnitude. The apparatus comprises the following items.
1. A curved wooden runway and its highest point, having a groove down which a steel ball may be rolled.
2. An object sphere support. This is an adjustable device which attaches to the mounting plate of the runway and will support a ball either exactly opposite the end of the runway for head-on collision or slightly offset for oblique impacts. 
3. A plumb-bob for making the plumb line.
4. Two spheres (steel ball bearing 19 mm. diameter.