曼昆哈佛大学经济学理第四章

1、the market forces of supply and demandchapter 4copyright 2001 by harcourt, inc.all rights reserved. requests for permission to make copies of any part of thework should be mailed to:permissions department, harcourt college publishers,6277 sea harbor drive, orlando, florida 32887-6777.harcourt, inc.

2、items and derived items copyright 2001 by harcourt, inc.the market forces of supply and demandusupply and demand are the two words that economists use most often.usupply and demand are the forces that make market economies work.umodern microeconomics is about supply, demand, and market equilibrium.h

3、arcourt, inc. items and derived items copyright 2001 by harcourt, inc.marketsua market is a group of buyers and sellers of a particular good or service. uthe terms supply and demand refer to the behavior of people . . . as they interact with one another in markets. harcourt, inc. items and derived i

4、tems copyright 2001 by harcourt, inc.markets u buyers determine demand.u sellers determine supply.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.market type: a competitive marketa competitive market is a market. . .with many buyers and sellers.that is not controlled by any on

5、e person.in which a narrow range of prices are established that buyers and sellers act upon.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.competition: perfect and otherwiseuproducts are the sameunumerous buyers and sellers so that each has no influence over priceubuyers and

6、sellers are price takersperfect competitionharcourt, inc. items and derived items copyright 2001 by harcourt, inc.competition: perfect and otherwiseumonopolyuone seller, and seller controls priceuoligopolyufew sellersunot always aggressive competitionharcourt, inc. items and derived items copyright

7、2001 by harcourt, inc.competition: perfect and otherwiseumonopolistic competitionumany sellersuslightly differentiated productsueach seller may set price for its own productharcourt, inc. items and derived items copyright 2001 by harcourt, inc.demandquantity demanded is the amount of a good that buy

8、ers are willing and able to purchase.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.law of demandthe law of demand states that there is an inverse relationship between price and quantity demanded.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.demand sc

9、hedulethe demand schedule is a table that shows the relationship between the price of the good and the quantity demanded. harcourt, inc. items and derived items copyright 2001 by harcourt, inc.demand schedulepricequantity$0.00120.50101.0081.5062.0042.5023.000harcourt, inc. items and derived items co

10、pyright 2001 by harcourt, inc.determinants of demandumarket priceuconsumer incomeuprices of related goodsutastesuexpectationsharcourt, inc. items and derived items copyright 2001 by harcourt, inc.demand curvethe demand curve is the downward-sloping line relating price to quantity demanded. harcourt,

11、 inc. items and derived items copyright 2001 by harcourt, inc.demand curve$3.002.502.001.501.000.502134 56789 101211price of ice-cream conequantity of ice-cream cones0priceq uantity$0.00120.50101.0081.5062.0042.5023.000harcourt, inc. items and derived items copyright 2001 by harcourt, inc.ceteris pa

12、ribusceteris paribus is a latin phrase that means all variables other than the ones being studied are assumed to be constant. literally, ceteris paribus means “other things being equal.”the demand curve slopes downward because, ceteris paribus, lower prices imply a greater quantity demanded!harcourt

13、, inc. items and derived items copyright 2001 by harcourt, inc.market demandumarket demand refers to the sum of all individual demands for a particular good or service.ugraphically, individual demand curves are summed horizontally to obtain the market demand curve.harcourt, inc. items and derived it

14、ems copyright 2001 by harcourt, inc.determinants of demandumarket priceuconsumer incomeuprices of related goodsutastesuexpectationsharcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity demanded versus change in demandchange in quantity demandedumovement along the

15、demand curve.ucaused by a change in the price of the product.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.changes in quantity demanded0d1price of cigarettes per packnumber of cigarettes smoked per daya tax that raises the price of cigarettes results in a movement along the

16、demand curve.ac202.00$4.0012harcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity demanded versus change in demandchange in demandua shift in the demand curve, either to the left or right.ucaused by a change in a determinant other than the price.harcourt, inc. ite

17、ms and derived items copyright 2001 by harcourt, inc.changes in demand0d1price of ice-cream conequantity of ice-cream conesd3d2increase in demanddecrease in demandharcourt, inc. items and derived items copyright 2001 by harcourt, inc.consumer incomeuas income increases the demand for a normal good w

18、ill increase.uas income increases the demand for an inferior good will decrease.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.consumer incomenormal good$3.002.502.001.501.000.502134 56789 101211price of ice-cream conequantity of ice-cream cones0increasein demandan increase i

19、n income.d1d2harcourt, inc. items and derived items copyright 2001 by harcourt, inc.consumer incomeinferior good$3.002.502.001.501.000.502134 56789 101211price of ice-cream conequantity of ice-cream cones0decreasein demandan increase in income.d1d2harcourt, inc. items and derived items copyright 200

20、1 by harcourt, inc.prices of related goodssubstitutes & complementsuwhen a fall in the price of one good reduces the demand for another good, the two goods are called substitutes.uwhen a fall in the price of one good increases the demand for another good, the two goods are called complements.har

21、court, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity demanded versus change in demandvariables that affect quantity demandeda change in this variable . . .pricerepresents a movementalong the demand curveincomeshifts the demand curveprices of relatedgoodsshifts the d

22、emand curvetastesshifts the demand curveexpectationsshifts the demand curvenumber ofbuyersshifts the demand curveharcourt, inc. items and derived items copyright 2001 by harcourt, inc.supplyquantity supplied is the amount of a good that sellers are willing and able to sell. harcourt, inc. items and

23、derived items copyright 2001 by harcourt, inc.law of supplythe law of supply states that there is a direct (positive) relationship between price and quantity supplied.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.determinants of supplyumarket priceuinput pricesutechnologyuex

24、pectations unumber of producersharcourt, inc. items and derived items copyright 2001 by harcourt, inc.supply schedulethe supply schedule is a table that shows the relationship between the price of the good and the quantity supplied. harcourt, inc. items and derived items copyright 2001 by harcourt,

25、inc.supply schedulepricequantity$0.0000.5001.0011.5022.0032.5043.005harcourt, inc. items and derived items copyright 2001 by harcourt, inc.supply curvethe supply curve is the upward-sloping line relating price to quantity supplied. harcourt, inc. items and derived items copyright 2001 by harcourt, i

26、nc.supply curve$3.002.502.001.501.000.5021345 6789 101211price of ice-cream conequantity of ice-cream cones0pricequantity$0.0000.5001.0011.5022.0032.5043.005harcourt, inc. items and derived items copyright 2001 by harcourt, inc.market supplyumarket supply refers to the sum of all individual supplies

27、 for all sellers of a particular good or service.ugraphically, individual supply curves are summed horizontally to obtain the market supply curve.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.determinants of supplyumarket priceuinput pricesutechnologyuexpectations unumber of

28、 producersharcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity supplied versus change in supplychange in quantity suppliedumovement along the supply curve.ucaused by a change in the market price of the product.harcourt, inc. items and derived items copyright 2001

29、 by harcourt, inc.change in quantity supplied1 5price of ice-cream conequantity of ice-cream cones0s 1.00ac$3.00a rise in the price of ice cream cones results in a movement along the supply curve.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity supplied versu

30、s change in supplychange in supplyua shift in the supply curve, either to the left or right. ucaused by a change in a determinant other than price.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in supplyprice of ice-cream conequantity of ice-cream cones0s1s2s3increase

31、in supplydecrease in supplyharcourt, inc. items and derived items copyright 2001 by harcourt, inc.change in quantity supplied versus change in supplyvariables that affect quantity supplied a change in this variable . . . price represents a movement along the supply curve input prices shifts the supp

32、ly curve technology shifts the supply curve expectations shifts the supply curve number of sellers shifts the supply curve harcourt, inc. items and derived items copyright 2001 by harcourt, inc.supply and demand togetherequilibrium priceuthe price that balances supply and demand. on a graph, it is t

33、he price at which the supply and demand curves intersect.equilibrium quantityuthe quantity that balances supply and demand. on a graph it is the quantity at which the supply and demand curves intersect. harcourt, inc. items and derived items copyright 2001 by harcourt, inc.supply and demand together

34、pricequantity$0.0000.5001.0011.5042.0072.50103.0013pricequantity$0.00190.50161.00131.50102.0072.5043.001demand schedulesupply scheduleat $2.00, the quantity demanded is equal to the quantity supplied!harcourt, inc. items and derived items copyright 2001 by harcourt, inc.supplydemandprice of ice-crea

35、m conequantity of ice-cream conesequilibrium of supply and demand21345 6789 1012110$3.002.502.001.501.000.50equilibriumharcourt, inc. items and derived items copyright 2001 by harcourt, inc.price of ice-cream conequantity of ice-cream cones21345 678 9 1012110$3.002.502.001.501.000.50supplydemandsurp

36、lusexcess supplyharcourt, inc. items and derived items copyright 2001 by harcourt, inc.surpluswhen the price is above the equilibrium price, the quantity supplied exceeds the quantity demanded. there is excess supply or a surplus. suppliers will lower the price to increase sales, thereby moving towa

37、rd equilibrium.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.excess demandquantity ofice-cream conesprice ofice-creamcone$2.000123456789 10 11 12 13supplydemand$1.50shortageharcourt, inc. items and derived items copyright 2001 by harcourt, inc.shortagewhen the price is below

38、 the equilibrium price, the quantity demanded exceeds the quantity supplied. there is excess demand or a shortage. suppliers will raise the price due to too many buyers chasing too few goods, thereby moving toward equilibrium.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.thr

39、ee steps to analyzing changes in equilibriumudecide whether the event shifts the supply or demand curve (or both).udecide whether the curve(s) shift(s) to the left or to the right.uexamine how the shift affects equilibrium price and quantity.how an increase in demand affects the equilibriumprice ofi

40、ce-creamcone2.0007quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.d22. .resultingin a higherprice.$2.50103. .and a higherquantity sold.new equilibriumharcourt, inc. items and derived items copyright 2001 by harcourt, inc.harcourt, inc. items and d

41、erived items copyright 2001 by harcourt, inc.shifts in curves versus movements along curvesua shift in the supply curve is called a change in supply.ua movement along a fixed supply curve is called a change in quantity supplied.ua shift in the demand curve is called a change in demand.ua movement al

42、ong a fixed demand curve is called a change in quantity demanded.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.s2how a decrease in supply affects the equilibriumprice ofice-creamcone2.000123478 911 12quantity ofice-cream cones13demandinitial equilibriums1101. an earthquake r

43、educesthe supply of ice cream.newequilibrium2. .resultingin a higherprice.$2.503. .and a lowerquantity sold.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.what happens to price and quantity when supply or demand shifts? no change in supply an increase in supply a decrease in

44、supply no change in demand p same q same p down q up p up q down an increase in demand p up q up p ambiguous q up p up q ambiguous a decrease in demand p down q down p down q ambiguous p ambiguous q down harcourt, inc. items and derived items copyright 2001 by harcourt, inc.summaryueconomists use th

45、e model of supply and demand to analyze competitive markets.uthe demand curve shows how the quantity of a good depends upon the price.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.summaryuaccording to the law of demand, as the price of a good rises, the quantity demanded fal

46、ls.uin addition to price, other determinants of quantity demanded include income, tastes, expectations, and the prices of complements and substitutes.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.summaryuthe supply curve shows how the quantity of a good supplied depends upon

47、 the price.uaccording to the law of supply, as the price of a good rises, the quantity supplied rises.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.summaryuin addition to price, other determinants of quantity supplied include input prices, technology, and expectations.umarke

48、t equilibrium is determined by the intersection of the supply and demand curves.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.summaryusupply and demand together determine the prices of the economys goods and services.uin market economies, prices are the signals that guide th

49、e allocation of resources.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.graphical reviewharcourt, inc. items and derived items copyright 2001 by harcourt, inc.how an increase in demand affects the equilibriumprice ofice-creamcone2.000710quantity ofice-cream conessupplyinitia

50、lequilibriumd1harcourt, inc. items and derived items copyright 2001 by harcourt, inc.how an increase in demand affects the equilibriumprice ofice-creamcone2.000710quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.harcourt, inc. items and derived ite

51、ms copyright 2001 by harcourt, inc.how an increase in demand affects the equilibriumprice ofice-creamcone2.000710quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.d2new equilibrium$2.50harcourt, inc. items and derived items copyright 2001 by harcour

52、t, inc.how an increase in demand affects the equilibriumprice ofice-creamcone2.000710quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.d2new equilibrium2. .resultingin a higherprice.$2.50how an increase in demand affects the equilibriumprice ofice-c

53、reamcone2.000710quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.d2new equilibrium2. .resultingin a higherprice.$2.503. .and a higherquantity sold.harcourt, inc. items and derived items copyright 2001 by harcourt, inc.how an increase in demand affects the equilibriumprice ofice-creamcone2.000710quantity ofice-cream conessupplyinitialequilibriumd11. hot weather increasesthe demand for ice cream.d2new equilibrium2. .resultingin a higherprice.$2.5