经济学第三章.ppt

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1、The Market Forces of Supply and Demand,4,市场力量:需求与供给,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 fact

2、ors that affect demand or supply affect the market price and quantity of a good?How do markets allocate resources?,影响买者物品需求的因素有哪些？影响卖者物品供给的因素有哪些？供给与需求怎么决定物品出售的价格与数量？影响供给与需求的因素又是如何影响市场价格与数量？市场是如何配置资源的？,1,THE MARKET FORCES OF SUPPLY AND DEMAND,2,Markets and Competition,A market is a group of buyers an

3、d 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”we assume markets are perf

4、ectly competitive.,市场是由某种物品或劳务的买者与卖者组成的一个群体竞争市场是有许多买者与卖者，以至于每个人对市场价格的影响都微乎其微的市场在一个完全竞争市场里：可供销售的物品是完全相同买者与卖者人数众多，没有任何一个买者或卖者可以影响市场价格，也就是说，每个人都是“价格接受者”本章假定市场是完全竞争的,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

5、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,物品的需求量是买者愿意并且能够购买的一种物品的数量需求定理：在其他条件不变时，一种物品的价格上升，对该物品的需求量减少,0,THE MARKET FORCES OF SUPPLY AND DEMAND,4,The Demand Schedule,Demand schedule:a table that shows the re

6、lationship between the price of a good and the quantity demanded Example:Helens demand for lattes,0,需求表：表示一种物品的价格与需求量之间关系的表格例如:海伦对拿铁咖啡的需求,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 t

7、he 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,T

8、he 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,需求曲线表示在其他条件不变的情况下，价格与需求量之间关系的图形这些“其他条件”是决定需求的非价

9、格因素（也就是决定买者对物品需求的除开物品价格的其他因素）改变它们会引起需求曲线的移动,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.,买者数量的增加会增加每一种价格水平下需求量，并使需求曲线向右移动,0,THE MARKET FORCES OF SUPPLY AND DEMAND,10,Suppose th

10、e 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 Curve Shifters:Income,Demand for a normal good is positively related to income.Increase in income causes increase in quantity demand

11、ed 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.),正常物品的需求与收入成正比：收入增加会增加每种价格水平下的需求量，并使需求曲线向右移动（低档物品的需求与收入成反比，收入增加会使低档物品的需求曲线向左移动）,0,THE MARKET FORCES OF SUPPLY AND DEMAND,12,

12、Demand Curve Shifters:Prices of Related Goods,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 exam

13、ples:Coke and Pepsi,laptops and desktop computers,CDs and music downloads,替代品：一种物品价格上升引起另一种物品需求量增加的两种物品例如，皮萨与汉堡包。皮萨价格的上升会增加汉堡包的需求，并使汉堡包的需求曲线向右移动其它例子：可口可乐与百事可乐，笔记本电脑与台式电脑，CD与音乐下载,0,THE MARKET FORCES OF SUPPLY AND DEMAND,13,Demand Curve Shifters:Prices of Related Goods,Two goods are complements if an

14、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,互

15、补品：一种物品价格上升引起另一种物品需求量减少的两种物品例如，电脑与软件。如果电脑价格上升，那人们会减少电脑的购买，因此也会减少软件的购买。软件的需求曲线向左移动其它例子：大学学费与教材，百吉饼与奶油乳酪，鸡蛋与咸肉,0,THE MARKET FORCES OF SUPPLY AND DEMAND,14,Demand Curve Shifters:Tastes嗜好,Anything that causes a shift in tastes toward a good will increase demand for that good and shift its D curve to the

16、 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.,对一种物品嗜好的增加会使那种物品的需求增加，并使它的需求曲线向右移动比如，阿特金斯饮食法在90年代开始流行，这引起对鸡蛋的需求增加，使鸡蛋的需求曲线向右移动,0,THE MARKET FORCES OF SUPPLY AND DEMAND,15,Demand Curve Shifters:Expectations,Expe

17、ctations 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.,预期会影响消费者的购买决定例如:如果人们预期他们的收入将增加，他们对于昂贵餐厅

18、的饮食需求现在就可能增加如果经济不好，人们会担心他们未来的就业保障，现在对新汽车的需求就可能减少,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 curveTa

19、stesshifts 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?,A C T I V E L

20、 E A R N I N G 1 A.Price of iPods falls,18,Music downloads and iPods are complements.A fall in price of iPods shifts the demand curve for music downloads to the right.,A C T I V E L E A R N I N G 1 B.Price of music downloads falls,19,The D curve does not shift.Move down along curve to a point with l

21、ower P,higher Q.,Price of music down-loads,Quantity of music downloads,D1,P1,Q1,A C T I V E L E A R N I N G 1 C.Price of CDs falls,20,CDs and music downloads are substitutes.A fall in price of CDs shifts demand for music downloads to the left.,Price of music down-loads,Quantity of music downloads,TH

22、E MARKET FORCES OF SUPPLY AND DEMAND,21,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,供给量：卖者愿意并且能够出售的一种物品的数量供给定理：在其他条件不变时，一种物品价格上升

23、，该物品供给量增加,0,THE MARKET FORCES OF SUPPLY AND DEMAND,22,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.,0,供给表：表示一种物品的价格与供给量之间关系的表格例如：星巴克拿铁咖啡的供应,THE MARKET FORCES OF SUPPLY AND DEMAND,23,St

24、arbucks 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,0,24,THE MARKET FOR

25、CES OF SUPPLY AND DEMAND,25,The Market Supply Curve,0,THE MARKET FORCES OF SUPPLY AND DEMAND,26,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,供给曲线表示其他

26、条件不变的情况下，一种物品的价格与供给量之间的关系这里的“其他条件”是决定供应的非价格因素改变这些非价格因素会使供给曲线移动,0,THE MARKET FORCES OF SUPPLY AND DEMAND,27,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 q

27、uantity at each price,and the S curve shifts to the right.,投入品价格的例子：工资，原材料价格投入品价格的下降会使在每个产品并价格下都更有利可图。因此企业会在每个价格下供应更多的数量，使供给曲线向右移动,0,THE MARKET FORCES OF SUPPLY AND DEMAND,28,Suppose the price of milk falls.At each price,the quantity of Lattes supplied will increase(by 5 in this example).,Supply Cur

28、ve Shifters:Input Prices,0,THE MARKET FORCES OF SUPPLY AND DEMAND,29,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.,技术决定

29、生产一单位的产出品需要多少投入品一个节约成本的技术改进与投入品价格下降一样有相同的作用，使供给曲线向外移动。,0,THE MARKET FORCES OF SUPPLY AND DEMAND,30,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.,卖者数量的增加使供给数量在每一个价格水平下都会增加，并使供给曲线向右移动,0,THE MARKET FORCE

30、S OF SUPPLY AND DEMAND,31,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 sup

31、ply*when their expectations of future prices change.(*If good not perishable),中东事件会导致高油价预期作为回应，得克萨斯的油田所有者现在会减少供给，储备一部分石油以便过段时间以更高的价格出售供给曲线向左移动 卖者一般都会根据未来价格变化的预期调整他们物品的供给（如果物品不是易腐的）,0,THE MARKET FORCES OF SUPPLY AND DEMAND,32,Summary:Variables that Influence Sellers,VariableA change in this variable,

32、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,33,Draw a supply curve for tax return preparation software.What happens to it in each of the foll

33、owing 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.,画出报税表编制软件的供给曲线，在下述情形下将会如何？,A.零售商降低软件的价格B.一项技术进步使软件能以更低的成本生产C.职业报税表编制人员提高他们提供服务的价格,A

34、C T I V E L E A R N I N G 2 A.Fall in price of tax return software,34,S curve does not shift.Move down along the curve to a lower P and lower Q.,A C T I V E L E A R N I N G 2 B.Fall in cost of producing the software,35,S curve shifts to the right:at each price,Q increases.,Price of tax return softwa

35、re,Quantity of tax return software,S1,P1,Q1,A C T I V E L E A R N I N G 3 C.Professional preparers raise their price,36,This shifts the demand curve for tax preparation software,not the supply curve.,THE MARKET FORCES OF SUPPLY AND DEMAND,37,Supply and Demand Together供给与需求的结合,Equilibrium:P has reach

36、ed the level where quantity supplied equals quantity demanded,0,均衡：市场价格达到使供给量与需求量相等的水平时的状态,THE MARKET FORCES OF SUPPLY AND DEMAND,38,Equilibrium price:均衡价格,the price that equates quantity supplied with quantity demanded使供给与需求平衡的价格,0,THE MARKET FORCES OF SUPPLY AND DEMAND,39,Equilibrium quantity:,the

37、 quantity supplied and quantity demanded at the equilibrium price,0,THE MARKET FORCES OF SUPPLY AND DEMAND,40,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 MAR

38、KET FORCES OF SUPPLY AND DEMAND,41,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,42,Surp

39、lus(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,43,Sho

40、rtage(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,44,Shortage(a.k.a.excess demand):,when quantity demanded is greater than quant

41、ity 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,45,Shortage(a.k.a.excess demand):,when quantity demanded is greater than quantity supplied,Facing a shortage,sellers raise the price,causing Q

42、D to fall,and QS to rise.,Shortage,Prices continue to rise until market reaches equilibrium.,0,THE MARKET FORCES OF SUPPLY AND DEMAND,46,Three Steps to Analyzing Changes in Eqm分析均衡变动的三个步骤,To determine the effects of any event,1.Decide whether event shifts S curve,D curve,or both.2.Decide in which di

43、rection curve shifts.3.Use supply-demand diagram to see how the shift changes eqm P and Q.,分析均衡的变动：1.确定该事件是使供给曲线移动还是使需求曲线移动（还是使两者都移动）2.确定曲线移动的方向3.用供求图说明这种移动如何改变均衡价格和均衡数量,THE MARKET FORCES OF SUPPLY AND DEMAND,47,EXAMPLE:The Market for Hybrid Cars混合动力汽车市场,THE MARKET FORCES OF SUPPLY AND DEMAND,48,STE

44、P 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

45、: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,49,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 carefu

46、l to distinguish b/w a shift in a curve and a movement along the curve.,仔细区分供给/需求曲线的移动和沿着供给/需求曲线的移动,Terms for Shift vs.Movement Along Curve曲线移动与沿曲线移动,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:

47、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,供给变动:影响供给变动的非价格因素使供给曲线移动（比如技术或投入品成本）供给量的变

48、动：沿着一条固定供给曲线的变动需求变动:影响需求变动的非价格因素使需求曲线移动（比如收入或买者的数量）需求量的变动：沿着一条固定需求曲线的变动,50,THE MARKET FORCES OF SUPPLY AND DEMAND,51,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 right

49、because 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,52,EXAMPLE 3:A Shift in Both Supp

50、ly 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,53,EXAMPLE 3:A Shift in Both