1. Module Supply and Demand: Supply and Equilibrium6
KRUGMAN'S
MACROECONOMICS for AP*
Margaret Ray and David Anderson

2. What you will learn in this Module:
What the supply curve is
The difference between movements along the supply curve and changes in supply
The factors that shift the supply curve
How supply and demand curves determine a market's equilibrium price and equilibrium quantity
In the case of a shortage or surplus, how price moves the market back to equilibrium

3. The Supply Schedule and the Supply Curve
Quantity supplied
Supply Curve
Law of supply
Supply is a schedule, which shows amounts of a product a producer is willing and able to produce and sell at each of a series of possible prices during a specified time period.
The schedule shows what quantities will be offered at various prices or what price will be required to induce various quantities to be offered.
The supply schedule shows that when the price is high, the quantity of sodas supplied is high. This relationship is known as the Law of Supply.
The Law of supply is believed to hold true for most products.
1. All else equal, as the price rises, quantity supplied rises.
2. Restated: There is a direct relationship between price and quantity supplied.
3. Note the “all else equal” assumption refers to a handful of other factors that affect the supply of a good. These will be covered shortly.

4. Supply Schedule and Supply Curve
Price
Quantity
$ 8 22
$ 7 14
$ 6 8
$ 5 6
$ 4 5
$ 3 4
$ 2 3
Price
Quantity

5. Understanding Shifts of the Supply Curve
Increase = right, decrease = left
T.R.I.C.E. shifts supply
Technology
Related prices (complements in production, substitutes in production)
Input prices
Competition (number of producers)
Expectations
There are several “shifters” of supply or the “other things,” besides price, which affect supply.
Changes in a shifter cause changes in supply.
If supply has increased, it has shifted to the right. At any price, firms wish to produce more.
If supply has decreased, it has shifted to the left. At any price, firms with to produce less.
1. Input (Resource) prices
A rise in an input price will cause a decrease in supply or leftward shift in supply curve; a decrease in an input price will cause an increase in supply or rightward shift in the supply curve. An increase in the price of fertilizer would cause a decrease in supply of corn.
2. Prices of related goods or services
If the price of a substitute production good rises, producers might shift production toward the higher priced good causing a decrease in supply of the original good. An increase in the price of soybeans may cause a farmer to decrease the supply of corn.
3. Technology
A technological improvement means more efficient production and lower costs, so an increase in supply or rightward shift in the curve results. Genetically improved seeds will increase supply of corn.
4. Expectations
Expectations about the future price of a product can cause producers to increase or decrease current supply.
Expectations of higher corn prices (next month) may cause farmers to decrease supply to the market today.
5. Number of sellers
Generally, the larger the number of sellers the greater the supply.

6. Supply, Demand, and Equilibrium
Equilibrium price
Equilibrium quantity
Market-clearing price
One way to think about equilibrium is like a stopped pendulum. Once a pendulum has started, it should continue to swing back and forth, never stopping. If you stop it, it will never restart the swinging. That’s equilibrium in the market. There are no changes in price, quantity demand, or quantity supply.
Think stability.

7. Finding the Equilibrium Price and Quantity

8. Why Does the Market Price Fall If It Is Above the Equilibrium Price?
Ask the students what happens to the price of many items (like sweaters) right after Christmas. Most will agree that there are widespread “after Christmas” sales on clothes, electronics, and even cars.
Why?
Because the store has too many items that went unsold prior to Christmas. In other words, they have a surplus of sweaters, and the best way to get rid of a surplus of sweaters, is to lower the price.
Surplus = Qs – Qd
Surplus
Producer's Incentive

9. Why Does the Market Price Rise If It is Below the Equilibrium Price?
Shortage
Consumer's Incentive
The tendency towards equilibrium
Imagine an auction where there is only one thing up for sale (like a valuable painting) and many people who wish to buy it.
What happens? The auctioneer begins to raise the price and the number of bidders begins to fall. Eventually all but one bidder has been eliminated because the price got so high that all others dropped out.
When you have a shortage of something, the best way to eliminate the shortage is to increase the price.
Shortage = Qd – Qs

10. Figure 6.1 The Supply Schedule and the Supply Curve Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

11. Figure 6.2 An Increase in Supply Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

12. Figure 6.3 Movement Along the Supply Curve Versus Shift of the Supply Curve Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

13. Figure 6.4 Shifts of the Supply Curve Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

14. Figure 6.5 The Individual Supply Curve and the Market Supply Curve Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

15. Table 6.1 Factors That Shift Supply Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

16. Figure 6.6 Market Equilibrium Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

17. Figure 6.7 Price Above Its Equilibrium Level Creates a Surplus Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers

18. Figure 6.8 Price Below Its Equilibrium Level Creates a Shortage Ray and Anderson: Krugman’s Economics for AP, First Edition Copyright © 2011 by Worth Publishers