The proportionality constant is a numerical factor that relates two quantities that are proportional to each other. When one quantity changes, the other changes in a consistent way, and the proportionality constant helps to define that relationship mathematically. For example, in the equation y = kx , k is the proportionality constant, where y and x are the variables being compared. This constant is crucial in various fields, including physics and economics, as it allows for predictions and calculations based on known values. In the context of Ohm's Law, for instance, the proportionality constant represents resistance, linking voltage and current in an electrical circuit.