Movements Along the Demand Curve
A movement along the demand curve represents the response of the quantity demanded to changes in price. On the demand curve graph, an increase in price causes an upward movement along the demand curve, while a decrease in price results in a downward movement.
Graph: Movements Along the Demand Curve
As seen in the graph, if we start at a price of 40, represented by point D on the demand curve, the quantity demanded is 400. If the price increases from 40 to 60, we move up the demand curve to point C, and the quantity demanded decreases to 200. Conversely, if the price falls from 40 to 20, we move down the demand curve to point E, and the quantity demanded increases to 600.
If any other variable that can affect the quantity demanded changes, such as consumer income or the prices of substitute and complementary goods, it causes a shift in the demand curve rather than a movement along it. The term "change in demand" usually refers to shifts in the demand curve, while "changes in the quantity demanded" refers to movements along the demand curve.