Relative velocity: Three electric cars on tracks make chalk line.

Relative Velocity: Motorized Cars and Track Board. Apparatus consists of a large board (4'x6') fitted with parallel tracks. Electric cars 'A' and 'B' run on these parallel tracks. These two cars are arranged to support a bridge between them, and this moving bridge carries a third electric car 'C'. The angle and speed of the car 'C' may be varied so that the chalk trace it makes on the large board changes with the different conditions. Set up notes: Place cars in their starting positions. Line up the pin on car A with the line on the bridge track. Lock down the knobs holding the bridge track to car B.