Day 4: Lesson Rate of Change (Slope) Average Speed as Rate of Change A rate of change is a rate that describes how one quantity changes in relation to another quantity. rise run is called the rate of change or slope It is a measure of the steepness of a line. The rate of change of a distance-time graph is the average speed. The rate of change can be positive or negative. The of the roof of a house is referred to as the of the roof by home builders. Engineers refer to the of a road as the . They often represent the rate of change as a .