The purpose of a control system is to maintain a desired output automatically, in spite of most events in the environment. The most familiar control systems are located within our own bodies. We maintain balance through a complex control system involving vision, the inner ear and muscles; and control or respiration rate to supply sufficient oxygen to the vital organs. Students explore some of these natural systems by exploring loss of balance when standing on one foot, and change of respiration rate before and after exercise. Every automatic control system includes five major components: a) a goal; b) a variable; c) a reference or desired level of the variable; d) a sensor, which detects the actual value of the variable; and e) an actuator, which tries to close the gap between the reference and actual levels of the variable. In human temperature regulation, for example, the goal is to maintain body temperature for optimum function of vital organs; the variable is the actual temperature; the reference level is about 98.6F, except in case of fever; the sensor is located in the hypothalamus section of the brain; and the actuators include sweat glands, which lower the temperate when it is too high, and the shivering mechanism, which does the opposite. Students conduct a “scavenger hunt” for control systems in the immediate environment, and discover them in elevators, bathrooms, energy-saving automatic light switches and thermostat-based environmental control. In each case they identify
