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1、C H A P T E R4What 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 marke
2、ts 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？1THE MARKET FORCES OF SUPPLY AND DEMAND2Markets and CompetitionA market is a group of buyers and sellers of a particular product. A competitive market is one with many buyers and sellers, each
3、 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 perfectly competitive. 市场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
4、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THE MARKET FORCES OF SUPPLY AND DEMAND3DemandThe 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
5、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：在其他条件不需求定理：在其他条件不变时，一种物品的价格上变时，一种物品的价格上升，对该物品的需求量减升，对该物品的需求量减少少THE MARKET FORCES OF SUPPLY AND DEMAND4The Demand ScheduleDemand schedule: a table that shows the relationship between the price of a good and the quantity dem
6、anded Example: Helens demand for lattesPrice of lattesQuantity of lattes demanded$0.00161.00142.00123.00104.0085.0066.004需求表：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 DEMAND5Price of LattesQuantity of LattesHelens Demand Schedule & CurvePrice of lattesQuantity of lattes de
7、manded$0.00161.00142.00123.00104.0085.0066.004Market Demand versus Individual DemandThe 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)46810121416Helens Qd 2
8、345678Kens Qd +=691215+=18+=21+=24Market Qd $0.006.005.004.003.002.001.00Price 6THE MARKET FORCES OF SUPPLY AND DEMAND7PQThe Market Demand Curve for LattesPQd (Market)$0.00241.00212.00183.00154.00125.0096.006THE MARKET FORCES OF SUPPLY AND DEMAND8Demand Curve ShiftersThe demand curve shows how price
9、 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”是决定需求的非价格因素（也就是决定买者对物品需求的除开物品价格
10、的其他因素）改变它们会引起需求曲线的移动THE MARKET FORCES OF SUPPLY AND DEMAND9Demand Curve Shifters: # of BuyersIncrease 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THE MARKET FORCES OF SUPPLY AND DEMAND10PQSuppose the number of buyers increase
11、s. Then, at each P, Qd will increase (by 5 in this example).Demand Curve Shifters: # of BuyersTHE MARKET FORCES OF SUPPLY AND DEMAND11Demand Curve Shifters: IncomeDemand for a normal good is positively related to income. Increase in income causes increase in quantity demanded at each price, shifts D
12、 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）THE MARKET FORCES OF SUPPLY AND DEMAND12Demand Curve Shifters: Price
13、s of Related GoodsTwo 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, l
14、aptops and desktop computers, CDs and music downloads 替代品替代品：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THE MARKET FORCES OF SUPPLY AND DEMAND13Demand Curve Shifters: Prices of Related GoodsTwo goods are complements if an increase in the price
15、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互补品互补品：一种物品价格上
16、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THE MARKET FORCES OF SUPPLY AND DEMAND14Demand Curve Shifters: Tastes嗜好嗜好Anything that causes a shift in tastes toward a good will increase demand for that good and shift its D curve to the 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
