Movement Along The Demand Curve & Shift of The Demand Curve

Movement Along The Demand Curve &Shift of The Demand Curve

Economists usually mean something different when they talk about a 'change in the quantity demanded' than when they talk about 'change in demand'. In economics we tend to draw a distinction between these two terms. We should keep this distinction clearly in mind so as to avoid any possibility of confusion.

Change in Quality Demanded - Movement along the Demand curve 

When the amount demanded of a commodity changes (rises or falls) as a result of change in its own price, while other determinants of demand (like income, tastes and prices of related goods) remain constant, it is known as change in quantity demanded.
Change in Quantity demanded may be of two types:  (i) extension of demand,  (ii) contraction of demand

  (i) Extension of demand: When the quantity demanded of a commodity rises due to fall in its price, other things remaining the same, it is called 'rise in quantity demanded' or 'extension of demand'.
For example, when the price of apples falls from ₹60 to ₹50 per kg, a consumer's purchase

  (ii) Contraction of demand: 'Contraction of demand' or 'fall in the quantity demanded' refers to a decrease in the quantity demanded of a commodity as a result in its rise of its price, other things remaining the same.
For example, when the price of apples rises from ₹30 a kg to ₹40 a kg, a consumer buys less apples, 4 kg instead of 6 kg, in this case there is contraction in demand or decrease in quantity demanded.

Any point on a demand curve represents a particular quantity being bought at a specified price. Different points on a demand curve represents different quantities demanded at different prices. A movement down the demand curve is called a 'rise in the quantity demanded' or 'extension of demand'. On the other hand, a movement up the demand curve is called a 'fall in quantity demanded' or 'contraction 
demand'.

                
                                                   Movement along the demand curve

Change in demand - Shift in demand curve

When the amount purchased of a commodity rises or falls because of change in factors other than the own price of the commodity, it is called change in demand.
Change in demand may be of two types:  (1) Increase in Demand,  (2) Decrease in Demand.


(i) Increase in Demand: Increase in demand refers to a situation when the consumers buy larger amount of commodity at the same price because of change in factors other than the own price of the commodity. Increase in demand may take place due to rise in income, a change in taste in favour of the commodity, rise in prices of substitutes, fall in prices of complimentary goods, increase in population, redistribution of  income, etc.

(ii) Decrease in Demand: Decrease in Demand refers to a situation when the consumers buy a smaller quantity of commodity at the same price. Decrease in demand takes place as a result in change of factors other than the own price of the commodity under question.

Change in demand is illustrated below:

Shift in Demand