A shift, or change, in demand does not necessarily lead to a new demand curve that is parallel with the old curve. When demand shifts, the slope and even the curvature of the demand curve can change as well. To the right we show a decrease in demand that might result from a change in tastes where the slope of the demand curve changes when demand shifts.
When demand shifts from D1 to D2, less is demanded at every price. When the market price is 3, the desired quantity demanded is 11.5 units on demand curve D1 , while only 4 units are demanded on curve D2. When the market price is 6, desired quantity demanded is 7 unit on curve D1, while 2 units are demanded on curve D2. No matter what the price, less will be demanded on curve D2 than at the same price on curve D1 .
D1 can be expressed with the following equation:
QD1 = 16 - (3/2)*P
D2 can be written:
QD2 = 6 - (2/3)*P