EM - Supply and Demand [LESSON]

Supply and Demand

To appreciate how perfect competition works, we need to understand how buyers and sellers interact in a market to set prices. In a market characterized by perfect competition, price is determined through the mechanisms of supply and demand. Prices are influenced both by the supply of products from sellers and by the demand for products by buyers.

To illustrate this concept, let's create a supply and demand schedule for one particular good sold at one point in time. Then we'll define demand and create a demand curve and define supply and create a supply curve. Finally, we'll see how supply and demand interact to create an equilibrium price—the price at which buyers are willing to purchase the amount that sellers are willing to sell.

Demand and the Demand Curve

Demand is the quantity of a product that buyers are willing to purchase at various prices. The quantity of a product that people are willing to buy depends on its price. You're typically willing to buy less of a product when prices rise and more of a product when prices fall. Generally speaking, we find products more attractive at lower prices, and we buy more at lower prices because our income goes further.

Demand Curve - The graph shows how as the price falls the quantity demanded increases.

Using this logic, we can construct a demand curve that shows the quantity of a product that will be demanded at different prices. Let's assume that the diagram in the figure "The Demand Curve" represents the daily price and quantity of apples sold by farmers at a local market. Note that as the price of apples goes down, buyers' demand goes up. Thus, if a pound of apples sells for $0.80, buyers will be willing to purchase only fifteen hundred pounds per day. But if apples cost only $0.60 a pound, buyers will be willing to purchase two thousand pounds. At $0.40 a pound, buyers will be willing to purchase twenty five hundred pounds.

Supply and the Supply Curve

Supply is the quantity of a product that sellers are willing to sell at various prices. The quantity of a product that a business is willing to sell depends on its price. Businesses are more willing to sell a product when the price rises and less willing to sell it when prices fall. Again, this fact makes sense: businesses are set up to make profits, and there are larger profits to be made when prices are high.

Supply curve - the graph shows that as the price increases the quantity businesses are willing to supply increases.

Now we can construct a supply curve that shows the quantity of apples that farmers would be willing to sell at different prices, regardless of demand. As you can see in the figure "The Supply Curve", the supply curve goes in the opposite direction from the demand curve: as prices rise, the quantity of apples that farmers are willing to sell also goes up. The supply curve shows that farmers are willing to sell only a thousand pounds of apples when the price is $0.40 a pound, two thousand pounds when the price is $0.60, and three thousand pounds when the price is $0.80.

Equilibrium Price

We can now see how the market mechanism works under perfect competition. We do this by plotting both the supply curve and the demand curve on one graph, as we've done in the figure "The Equilibrium Price". The point at which the two curves intersect is the equilibrium price. At this point, buyers demand for apples and sellers' supply of apples is in equilibrium.

Equilibrium Price - The graph shows both the demand and supply curves. Where the two curve intersect (supply = demand) is the equilibrium price.

You can see in the figure "The Equilibrium Price" that the supply and demand curves intersect at the price of $0.60 and quantity of two thousand pounds. Thus, $0.60 is the equilibrium price: at this price, the quantity of apples demanded by buyers equals the quantity of apples that farmers are willing to supply. If a farmer tries to charge more than $0.60 for a pound of apples, he won't sell very many and his profits will go down. If, on the other hand, a farmer tries to charge less than the equilibrium price of $0.60 a pound, he will sell more apples but his profit per pound will be less than at the equilibrium price.

What have we learned in this discussion? We've learned that without outside influences, markets in an environment of perfect competition will arrive at an equilibrium point at which both buyers and sellers are satisfied. But we must be aware that this is a very simplistic example. Things are much more complex in the real world. For one thing, markets rarely operate without outside influences. Sometimes, sellers supply more of a product than buyers are willing to purchase; in that case, there's a surplus. Sometimes, they don't produce enough of a product to satisfy demand; then we have a shortage.

Circumstances also have a habit of changing. What would happen, for example, if income rose and buyers were willing to pay more for apples? The demand curve would change, resulting in an increase in equilibrium price. This outcome makes intuitive sense: as demand increases, prices will go up. What would happen if apple crops were larger than expected because of favorable weather conditions? Farmers might be willing to sell apples at lower prices. If so, the supply curve would shift, resulting in another change in equilibrium price: the increase in supply would bring down prices.

Types of Demand

  • Elastic: A small change in price causes a significant change in demand.
  • Inelastic: Any change in price has little to no effect on demand.
    • No acceptable substitute.
    • Price change is small relative to buyer income.
    • Product is a perceived necessity.

Factors Affecting Demand

[CC BY 4.0] UNLESS OTHERWISE NOTED | IMAGES: LICENSED AND USED ACCORDING TO TERMS OF SUBSCRIPTION