If there is a change in quantity demanded due to a change in price of the commodity or service while other factors are held constant, it is known as changes in quantity demanded or extension / contraction of demand curve. When we show extension or contraction in a diagram, we remain on the same demand curve moving from one point to another point. Hence, it is also called movement along the demand curve. [note]
Extension of Demand
Other things remaining the same, higher quantity demanded due to a decrease in price, is termed as an extension of demand.
Contraction of Demand
Other things remaining the same, lower quantity demanded due to increase in price, is known as the contraction of demand
Extension/contraction of demand or movement along the demand curve are explained in the following table and diagram
In the given figure, we move along the same demand curve from one point to another point. This movement along the demand curve indicates extension or contraction of demand.
If we move downwards from left to right, it is called extension/expansion of demand. On the other hands, if we move upwards from right to left, it is called contraction of demand.
Note: Change in quantity demanded refers to a change from one point on a demand curve to another point, either on the original demand curve or a new one which appears due to a change in factors other than product’