微观经济学原理曼昆.ppt

The Market Forces of Supply and Demand,Economics,P R I N C I P L E S O F,N.Gregory Mankiw,4,In this chapter,look for the answers to these questions:,What factors affect buyers demand for goods?What factors affect sellers supply of goods?How do supply and demand determine the price of a good and the quantity sold?How do changes in the factors that affect demand or supply affect the market price and quantity of a good?How do markets allocate resources?,1,THE MARKET FORCES OF SUPPLY AND DEMAND,2,Markets and Competition,A market is a group of buyers and sellers of a particular product.A competitive market is one with many buyers and sellers,each has a negligible effect on price.In a perfectly competitive market:All goods exactly the sameBuyers&sellers so numerous that no one can affect market price each is a“price taker”In this chapter,we assume markets are perfectly competitive.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,3,Demand,The quantity demanded of any good is the amount of the good that buyers are willing and able to purchase.Law of demand:the claim that the quantity demanded of a good falls when the price of the good rises,other things equal,0,THE MARKET FORCES OF SUPPLY AND DEMAND,4,The Demand Schedule,Demand schedule:a table that shows the relationship between the price of a good and the quantity demanded Example:Helens demand for lattes.,Notice that Helens preferences obey the Law of Demand.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,5,Helens Demand Schedule&Curve,0,Market Demand versus Individual Demand,The quantity demanded in the market is the sum of the quantities demanded by all buyers at each price.Suppose Helen and Ken are the only two buyers in the Latte market.(Qd=quantity demanded),Market Qd,0,6,THE MARKET FORCES OF SUPPLY AND DEMAND,7,P,Q,The Market Demand Curve for Lattes,0,THE MARKET FORCES OF SUPPLY AND DEMAND,8,Demand Curve Shifters,The demand curve shows how price affects quantity demanded,other things being equal.These“other things”are non-price determinants of demand(i.e.,things that determine buyers demand for a good,other than the goods price).Changes in them shift the D curve,0,THE MARKET FORCES OF SUPPLY AND DEMAND,9,Demand Curve Shifters:#of Buyers,Increase in#of buyers increases quantity demanded at each price,shifts D curve to the right.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,10,Suppose the number of buyers increases.Then,at each P,Qd will increase(by 5 in this example).,0,Demand Curve Shifters:#of Buyers,THE MARKET FORCES OF SUPPLY AND DEMAND,11,Demand for a normal good is positively related to income.Increase in income causes increase in quantity demanded at each price,shifts D curve to the right.(Demand for an inferior good is negatively related to income.An increase in income shifts D curves for inferior goods to the left.),Demand Curve Shifters:Income,0,THE MARKET FORCES OF SUPPLY AND DEMAND,12,Two goods are substitutes if an increase in the price of one causes an increase in demand for the other.Example:pizza and hamburgers.An increase in the price of pizza increases demand for hamburgers,shifting hamburger demand curve to the right.Other examples:Coke and Pepsi,laptops and desktop computers,CDs and music downloads,Demand Curve Shifters:Prices of Related Goods,0,THE MARKET FORCES OF SUPPLY AND DEMAND,13,Two goods are complements if an increase in the price of one causes a fall in demand for the other.Example:computers and software.If price of computers rises,people buy fewer computers,and therefore less software.Software demand curve shifts left.Other examples:college tuition and textbooks,bagels and cream cheese,eggs and bacon,Demand Curve Shifters:Prices of Related Goods,0,THE MARKET FORCES OF SUPPLY AND DEMAND,14,Anything that causes a shift in tastes toward a good will increase demand for that good and shift its D curve to the right.Example:The Atkins diet became popular in the 90s,caused an increase in demand for eggs,shifted the egg demand curve to the right.,Demand Curve Shifters:Tastes,0,THE MARKET FORCES OF SUPPLY AND DEMAND,15,Expectations affect consumers buying decisions.Examples:If people expect their incomes to rise,their demand for meals at expensive restaurants may increase now.If the economy sours and people worry about their future job security,demand for new autos may fall now.,Demand Curve Shifters:Expectations,0,THE MARKET FORCES OF SUPPLY AND DEMAND,16,Summary:Variables That Influence Buyers,VariableA change in this variable,Pricecauses a movement along the D curve#of buyersshifts the D curveIncomeshifts the D curvePrice ofrelated goodsshifts the D curveTastesshifts the D curveExpectationsshifts the D curve,0,A.The price of iPods fallsB.The price of music downloads fallsC.The price of CDs falls,A C T I V E L E A R N I N G 1 Demand Curve,17,Draw a demand curve for music downloads.What happens to it in each of the following scenarios?Why?,THE MARKET FORCES OF SUPPLY AND DEMAND,18,Supply,The quantity supplied of any good is the amount that sellers are willing and able to sell.Law of supply:the claim that the quantity supplied of a good rises when the price of the good rises,other things equal,0,THE MARKET FORCES OF SUPPLY AND DEMAND,19,The Supply Schedule,Supply schedule:A table that shows the relationship between the price of a good and the quantity supplied.Example:Starbucks supply of lattes.,Notice that Starbucks supply schedule obeys the Law of Supply.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,20,Starbucks Supply Schedule&Curve,P,Q,0,Market Supply versus Individual Supply,The quantity supplied in the market is the sum of the quantities supplied by all sellers at each price.Suppose Starbucks and Jitters are the only two sellers in this market.(Qs=quantity supplied),Market Qs,0,21,THE MARKET FORCES OF SUPPLY AND DEMAND,22,The Market Supply Curve,0,THE MARKET FORCES OF SUPPLY AND DEMAND,23,Supply Curve Shifters,The supply curve shows how price affects quantity supplied,other things being equal.These“other things”are non-price determinants of supply.Changes in them shift the S curve,0,THE MARKET FORCES OF SUPPLY AND DEMAND,24,Supply Curve Shifters:Input Prices,Examples of input prices:wages,prices of raw materials.A fall in input prices makes production more profitable at each output price,so firms supply a larger quantity at each price,and the S curve shifts to the right.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,25,Suppose the price of milk falls.At each price,the quantity of Lattes supplied will increase(by 5 in this example).,Supply Curve Shifters:Input Prices,0,THE MARKET FORCES OF SUPPLY AND DEMAND,26,Supply Curve Shifters:Technology,Technology determines how much inputs are required to produce a unit of output.A cost-saving technological improvement has the same effect as a fall in input prices,shifts S curve to the right.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,27,Supply Curve Shifters:#of Sellers,An increase in the number of sellers increases the quantity supplied at each price,shifts S curve to the right.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,28,Supply Curve Shifters:Expectations,Example:Events in the Middle East lead to expectations of higher oil prices.In response,owners of Texas oilfields reduce supply now,save some inventory to sell later at the higher price.S curve shifts left.In general,sellers may adjust supply*when their expectations of future prices change.(*If good not perishable),0,THE MARKET FORCES OF SUPPLY AND DEMAND,29,Summary:Variables that Influence Sellers,VariableA change in this variable,Pricecauses a movement along the S curveInput Pricesshifts the S curveTechnologyshifts the S curve#of Sellersshifts the S curveExpectationsshifts the S curve,0,A C T I V E L E A R N I N G 2 Supply Curve,30,Draw a supply curve for tax return preparation software.What happens to it in each of the following scenarios?,A.Retailers cut the price of the software.B.A technological advance allows the software to be produced at lower cost.C.Professional tax return preparers raise the price of the services they provide.,THE MARKET FORCES OF SUPPLY AND DEMAND,31,Supply and Demand Together,Equilibrium:P has reached the level where quantity supplied equals quantity demanded,0,THE MARKET FORCES OF SUPPLY AND DEMAND,32,Equilibrium price:,the price that equates quantity supplied with quantity demanded,0,THE MARKET FORCES OF SUPPLY AND DEMAND,33,Equilibrium quantity:,the quantity supplied and quantity demanded at the equilibrium price,0,THE MARKET FORCES OF SUPPLY AND DEMAND,34,Surplus(a.k.a.excess supply):,when quantity supplied is greater than quantity demanded,Surplus,Example:If P=$5,then QD=9 lattes,and QS=25 lattes,resulting in a surplus of 16 lattes,0,THE MARKET FORCES OF SUPPLY AND DEMAND,35,Surplus(a.k.a.excess supply):,when quantity supplied is greater than quantity demanded,Facing a surplus,sellers try to increase sales by cutting price.,This causes QD to rise,which reduces the surplus.,and QS to fall,0,THE MARKET FORCES OF SUPPLY AND DEMAND,36,Surplus(a.k.a.excess supply):,when quantity supplied is greater than quantity demanded,Facing a surplus,sellers try to increase sales by cutting price.,This causes QD to rise and QS to fall.,Surplus,Prices continue to fall until market reaches equilibrium.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,37,Shortage(a.k.a.excess demand):,when quantity demanded is greater than quantity supplied,Example:If P=$1,then QD=21 lattes,and QS=5 lattes,resulting in a shortage of 16 lattes,Shortage,0,THE MARKET FORCES OF SUPPLY AND DEMAND,38,Shortage(a.k.a.excess demand):,when quantity demanded is greater than quantity supplied,Facing a shortage,sellers raise the price,causing QD to fall,which reduces the shortage.,and QS to rise,0,THE MARKET FORCES OF SUPPLY AND DEMAND,39,Shortage(a.k.a.excess demand):,when quantity demanded is greater than quantity supplied,Facing a shortage,sellers raise the price,causing QD to fall,and QS to rise.,Shortage,Prices continue to rise until market reaches equilibrium.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,40,Three Steps to Analyzing Changes in Eqm,To determine the effects of any event,1.Decide whether event shifts S curve,D curve,or both.2.Decide in which direction curve shifts.3.Use supply-demand diagram to see how the shift changes eqm P and Q.,THE MARKET FORCES OF SUPPLY AND DEMAND,41,EXAMPLE:The Market for Hybrid Cars,THE MARKET FORCES OF SUPPLY AND DEMAND,42,STEP 1:D curve shifts because price of gas affects demand for hybrids.S curve does not shift,because price of gas does not affect cost of producing hybrids.,STEP 2:D shifts rightbecause high gas price makes hybrids more attractive relative to other cars.,EXAMPLE 1:A Shift in Demand,EVENT TO BE ANALYZED:Increase in price of gas.,STEP 3:The shift causes an increase in price and quantity of hybrid cars.,THE MARKET FORCES OF SUPPLY AND DEMAND,43,EXAMPLE 1:A Shift in Demand,P2,Q2,Notice:When P rises,producers supply a larger quantity of hybrids,even though the S curve has not shifted.,Always be careful to distinguish b/w a shift in a curve and a movement along the curve.,Terms for Shift vs.Movement Along Curve,Change in supply:a shift in the S curveoccurs when a non-price determinant of supply changes(like technology or costs)Change in the quantity supplied:a movement along a fixed S curve occurs when P changes Change in demand:a shift in the D curveoccurs when a non-price determinant of demand changes(like income or#of buyers)Change in the quantity demanded:a movement along a fixed D curveoccurs when P changes,44,THE MARKET FORCES OF SUPPLY AND DEMAND,45,STEP 1:S curve shifts because event affects cost of production.D curve does not shift,because production technology is not one of the factors that affect demand.,STEP 2:S shifts rightbecause event reduces cost,makes production more profitable at any given price.,EXAMPLE 2:A Shift in Supply,EVENT:New technology reduces cost of producing hybrid cars.,STEP 3:The shift causes price to fall and quantity to rise.,THE MARKET FORCES OF SUPPLY AND DEMAND,46,EXAMPLE 3:A Shift in Both Supply and Demand,EVENTS:price of gas rises AND new technology reduces production costs,STEP 1:Both curves shift.,STEP 2:Both shift to the right.,STEP 3:Q rises,but effect on P is ambiguous:If demand increases more than supply,P rises.,THE MARKET FORCES OF SUPPLY AND DEMAND,47,EXAMPLE 3:A Shift in Both Supply and Demand,STEP 3,cont.,EVENTS:price of gas rises AND new technology reduces production costs,But if supply increases more than demand,P falls.,A C T I V E L E A R N I N G 3 Shifts in supply and demand,48,Use the three-step method to analyze the effects of each event on the equilibrium price and quantity of music downloads.Event A:A fall in the price of CDsEvent B:Sellers of music downloads negotiate a reduction in the royalties they must pay for each song they sell.Event C:Events A and B both occur.,THE MARKET FORCES OF SUPPLY AND DEMAND,49,CONCLUSION:How Prices Allocate Resources,One of the Ten Principles from Chapter 1:Markets are usually a good way to organize economic activity.,In market economies,prices adjust to balance supply and demand.These equilibrium prices are the signals that guide economic decisions and thereby allocate scarce resources.,CHAPTER SUMMARY,A competitive market has many buyers and sellers,each of whom has little or no influence on the market price.Economists use the supply and demand model to analyze competitive markets.The downward-sloping demand curve reflects the Law of Demand,which states that the quantity buyers demand of a good depends negatively on the goods price.,50,CHAPTER SUMMARY,Besides price,demand depends on buyers incomes,tastes,expectations,the prices of substitutes and complements,and number of buyers.If one of these factors changes,the D curve shifts.The upward-sloping supply curve reflects the Law of Supply,which states that the quantity sellers supply depends positively on the goods price.Other determinants of supply include input prices,technology,expectations,and the#of sellers.Changes in these factors shift the S curve.,51,CHAPTER SUMMARY,The intersection of S and D curves determines the market equilibrium.At the equilibrium price,quantity supplied equals quantity demanded.If the market price is above equilibrium,a surplus results,which causes the price to fall.If the market price is below equilibrium,a shortage results,causing the price to rise.,52,CHAPTER SUMMARY,We can use the supply-demand diagram to analyze the effects of any event on a market:First,determine whether the event shifts one or both curves.Second,determine the direction of the shifts.Third,compare the new equilibrium to the initial one.In market economies,prices are the signals that guide economic decisions and allocate scarce resources.,53,