Movements along demand and supply curves

Demand and supply curves illustrate how the quantity of a product demanded or supplied changes in response to variations in its price, assuming all other influencing factors remain constant. These changes result in movements along the existing curves rather than shifts of the curves themselves.

How price changes affect demand

A demand curve slopes downwards, showing that as the price of a product falls, the quantity demanded rises, and vice versa:

• Extension of demand - An increase in quantity demanded due to a price decrease, represented by a movement down and to the right along the demand curve.
• Contraction of demand - A decrease in quantity demanded due to a price increase, shown as a movement up and to the left along the demand curve.

How price changes affect supply

A supply curve slopes upwards, indicating that as the price of a product rises, the quantity supplied increases, and vice versa:

• Extension of supply - An increase in quantity supplied in response to a price rise, depicted as a movement up and to the right along the supply curve.
• Contraction of supply - A decrease in quantity supplied following a price fall, illustrated by a movement down and to the left along the supply curve.

Shifts in the demand curve and their causes

The demand curve is constructed on the basis that all factors influencing demand, except the product's price, stay the same. When these non-price factors change, the entire demand curve shifts either to the right (increase in demand) or to the left (decrease in demand), meaning more or less is demanded at every price level.

Causes of an increase in demand

A rightward shift occurs when demand rises due to favourable changes in external factors:

• Rise in income - Higher consumer incomes enable greater purchasing power, boosting demand for normal goods.
• Increase in substitute prices - If the price of a competing product rises, consumers switch to the cheaper alternative, increasing demand.
• Decrease in complement prices - Lower prices for related goods (e.g., a drop in petrol prices increasing demand for cars) make the overall purchase more attractive.
• Positive changes in tastes and preferences - Shifts in fashion, attitudes, or trends that favour the product, such as growing popularity of eco-friendly items.

Causes of a decrease in demand

A leftward shift happens when demand falls owing to unfavourable external changes:

• Fall in income - Reduced incomes limit spending, decreasing demand for non-essential goods.
• Decrease in substitute prices - Cheaper alternatives draw consumers away, reducing demand for the original product.
• Increase in complement prices - Higher prices for linked goods (e.g., rising ink costs decreasing demand for printers) deter purchases.
• Negative changes in tastes and preferences - Unfavourable shifts in fashion or attitudes, like a decline in interest for outdated technology.

Shifts in the supply curve and their causes

The supply curve assumes that all determinants of supply, other than the product's price, remain unchanged. Changes in these non-price factors cause the supply curve to shift to the right (increase in supply) or to the left (decrease in supply), altering the quantity supplied at every price.

Causes of an increase in supply

A rightward shift reflects greater supply due to supportive changes in production conditions:

• Decrease in production costs - Lower expenses (e.g., cheaper raw materials) allow firms to supply more profitably.
• Expansion of the industry - More firms entering the market increases overall supply capacity.
• Fall in competitors' prices - Reduced prices from rivals may prompt suppliers to increase output to compete.
• Reduction in indirect taxes or rise in subsidies - Lower taxes or higher government support cuts effective costs, boosting supply.

Causes of a decrease in supply

A leftward shift indicates reduced supply from adverse changes:

• Increase in production costs - Higher expenses (e.g., rising wages) make supplying the same quantity less viable.
• Contraction of the industry - Fewer firms operating reduces total supply availability.
• Rise in competitors' prices - Higher rival prices might lead suppliers to redirect resources elsewhere.
• Increase in indirect taxes or fall in subsidies - Raised taxes or cut support increases costs, limiting supply.

The distinction between movements and shifts

Understanding the difference between movements along curves and shifts of curves is essential for analysing market changes accurately. Movements are price-driven, while shifts stem from broader economic factors.

Key differences in demand and supply changes:

• Movements along a curve - These occur solely due to changes in the product's own price, affecting quantity demanded or supplied without altering the curve's position.
• Shifts of a curve - These result from variations in non-price determinants, repositioning the entire curve.

The time factor in market adjustments

Markets do not adjust instantly to changes in demand or supply; the process unfolds over different time periods, allowing suppliers to respond gradually. Over time, producers adapt by reallocating resources. For instance, if consumer preferences shift toward organic food products causing a price increase, farmers will require time to convert conventional farmland to meet this higher demand.