Demand is the amount of a good that consumers are willing and able to buy at a given price. Utility varies from person to person. Some people get more satisfaction from eating chips than others. Even the same person can gain greater satisfaction by eating chips when hungry than when he has lost his appetite. The demand curve labelled DD in the figure below shows the amount of a good one or more consumers are willing and able to buy at different prices.
Demand Curves A change in price never shifts the demand curve for that good.
In the figure below an increase in price results in a movement up the demand curve. The fall in the quantity demanded from Q 1 to Q 2 is sometimes called a contraction in demand. A demand curve shifts only if there is a change in income, in taste or in the demand for substitutes or complements. In the diagram below a decrease in demand has shifted the demand curve to the left. The new demand curve is D1 D1.