This circuit represents a DC motor which is speed controlled by 4 bridge rectifiers and 5 switches. It is based on this control circuit: http://www.learningelectronics.net/circuits/dc-motor-speed-controller.html
When the most right switch is closed, the current has to flow through the 4 bridge rectifiers. This makes the voltage drop at each bridge rectifier, and so voltage to the motor is low and the motor will turn slow. With each bridge rectifier being bypassed, the voltage to the motor is increased until the left switch is closed and applies full voltage to the motor.
To make it more realistic in comparison to the circuit in the link, first close the next switch and open the previous one.
Enjoy!
