Final answer:
In cruise control, when a car's speed decreases below the set speed, the difference is known as an error signal. The cruise control system then provides negative feedback by increasing the throttle to get back to the set point.
Step-by-step explanation:
When using cruise control in a car at 70 mph and the speed drops to 65 mph when climbing a hill, the car's computer detects the difference between these two speeds and adjusts accordingly. This difference is called an error signal. The error signal informs the system that there is a deviation from the desired set point, which is the target speed in cruise control. The cruise control then reacts by increasing the throttle to reduce this error and return the car back to the preset speed. This is a classic example of a negative feedback loop, working to maintain the controlled variable (car speed) at a set point.
Cruise control is an example of how technological systems use principles similar to those found in nature, such as physiological systems in the human body, which maintain steady states through feedback mechanisms. Understanding the role of the error signal helps to grasp the concept of how cruise control and other automated systems maintain desired operation levels.