• Demand
• The Law of Demand
• The Demand Curve
• Shifts in Demand Curve versus
Movement along a Demand Curve
• Individual and Market Demand Curve

Demand is the amount of goods that buyers are willing and able to purchase.
The air that we need to breathe everyday is our demand?

The Law of Demand:
Quantity demanded rises as price falls, other things constant.
Quantity demanded falls as price rises, other things constant.

• Demand Curve is a graph of the relationship between the price of a good and the quantity demanded .
Based on the law of demand, what’s kind of shape the demand curve should be like?

A Demand Table
A
B
C
D
E
Price per
DVD
DVD rentals demanded per week
$0.50
1.00
2.00
3.00
4.00
9
8
6
4
2
$6.00
A Demand Curve
5.00
4.00
3.50
3.00
E
D
2.00
C
Demand for DVDs
1.00
.50
B
A
0
1 2 3 4 5 6 7 8 9 10 11 1213
Quantity demanded of DVDs (per week)

• Quantity demanded refers to a specific amount that will be demanded per unit of time at a specific price, other things constant.
• Quantity demanded refers to a specific point on the demand curve.
• A change in quantity demanded , caused only by a change in the price of the good itself, is shown by a movement along a demand curve .

• Demand refers to a schedule of quantities of a good that will be bought per unit of time at various prices, other things constant.
• It refers to the entire demand curve .
• A change in demand , caused by anything other than the good’s own price, is shown by a shift in the demand curve .

$20
$10
Change in quantity demanded
B $20
Change in demand
A
0
D
1
100 200
Quantity demanded
$10
B
A
D
0
100 200
Quantity demanded
D
1

• Normal good is the good that an increase in income leads to an increase in demand , other things constant.
• Inferior good is the good that an increase in income leads to a decrease in demand , other things constant.

• Substitutes are often pairs of goods that are used in place of each other and an increase in the price of one leads to an increase in the demand for the other.
• Complements are often pairs of goods that are used together and an increase in the price of one leads to a decrease in the demand for the other.

• Shift factors of demand are factors that cause changes in demand (shifts in the demand curve).
• Society’s Income
– An increase in income will increase demand for normal goods.
– An increase in income will decrease demand for inferior goods.

• Prices of Other Goods
– When the price of a substitute good falls, demand falls for the good whose price has not changed.
– When the price of a complement good falls, demand rises for the good whose price has not changed.
• Tastes
– A change in taste will change demand with no change in price.

• Expectations
– If you expect your income to rise, you may consume more now.
– If you expect prices to fall in the future, you may put off purchases today.
• Taxes and Subsidies
– Taxes increase the cost of goods, thereby reducing demand.
– Subsidies have an opposite effect.

Would a change in the price of pizza shift the pizza’s demand curve?

D
E
F
G
H
A
B
C
A market demand curve is the horizontal sum of all individual demand curves
$4.00
G
Price per
DVD
+
Alice’s demand
+
Bruce’s demand
+
Cathy’s demand
=
Market demand
3.50
F
3.00
$.0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
4
3
2
6
5
9
8
7
1
0
0
3
2
6
5
4
0
0
0
0
0
1
1
0
5
3
2
9
7
16
14
11
2.50
2.00
1.50
1.00
0.50
E
D
C
Cathy BruceAlice
A
0
B
2 4 6 8 10 12 14 16
Quantity demanded of DVD per week

• Supply
• The Law of Supply
• The Supply Curve
• A Shift in Supply Curve vs a Movement along a Supply Curve
• Individual and Market Supply Curve

• Supply is the amount of a good that sellers are willing and able to sell.
• The Law of Supply :
Quantity supplied rises as price rises, other things constant .
Quantity supplied falls as price falls, other things constant .

• Supply Curve is a graph of the relationship between the price of a good and the quantity supplied .
Based on the law of supply, what’s kind of shape the supply curve should be like?

• The supply curve is the graphic representation of the law of supply.
• The supply curve slopes upward to the right because the relationship between quantity supplied and the price is positive
• As price increases, the quantity supplied increases.
P
B
P
A
0
A
B
Q
A
Q
B
Quantity supplied
(per unit of time)
S

• Quantity supplied refers to a specific amount that will be supplied at a specific price.
• Quantity supplied refers to a specific point on the supply curve.
• A change in quantity supplied , caused only by a change in the price of the good itself, is shown by a movement along the supply curve.

• Supply refers to a schedule of quantities a seller is willing to sell per unit of time at various prices, other things constant.
• Supply refers to the whole supply curve .
• A change in supply , caused by anything other than the good’s price, is shown by a shift in the supply curve.

$36
$15
S
0
A
B
Change in quantity supplied
$15
Change in
Supply 0
S
1
A B
1700 1900
Barrels per year (millions)
1700 1800
Barrels per year (millions)

• Shift factors of supply are factors that cause changes in supply (shifts in the supply curve).
• Price of Inputs
– When costs go up, profits go down, so that the incentive to supply also goes down.
• Technology
– Advances in technology reduce the number of inputs needed to produce a given supply of goods, decreasing costs, increasing profits, leading to increased supply.

• Expectations
– If suppliers expect prices to rise in the future, they may store today’s supply to sell later, decreasing supply now.
• Taxes and Subsidies
– When taxes increase, costs go up, and profits go down, causing a decrease in supply.
– When subsidies increase, costs decrease, and profits increase, leading to an increase in supply.

Price
(per DVD)
Ann + Barry + Charlie =
Market supply
E
F
G
H
I
A
B
C
D
$0.00
0.50
1.00
1.50
2.00
2.50
3.00
3.50
4.00
0
1
2
3
4
5
6
7
8
0
0
1
2
3
4
5
5
5 by adding all quantities
0
0
0
0
0
0
0
2
2
Market supply is determined supplied at a given price.
0
1
3
5
7
9
11
14
15
$4.00
3.50
Charlie Barry Ann Market
Supply
H
I
3.00
G
2.50
F
2.00
E
1.50
D
1.00
0.50
0
C
B
C
A
A
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16
Quantity of DVDs supplied (per week)

Price
(per DVD)
$3.50
Q
S
Q
D
Surplus(+)
Shortage (-)
7 3 +4
$2.50
$1.50
5
3
5
7
0
-4
$5.00
4.00
3.50
3.00
2.50
2.00
1.50
1.00
A
Excess supply
E
C
S
Excess demand
1 2 3 4 5 6 7 8
D
Quantity of DVDs supplied and demanded (per week)

• Equilibrium is a situation in which supply and demand have been brought into balance.
• Equilibrium price is the price that balances supply and demand.
• Equilibrium quantity is the quantity supplied and quantity demanded when the price has adjusted to balance supply and demand

• When the market is not in equilibrium, there is either excess demand or excess supply.
• Excess supply – a surplus, the quantity supplied is greater than the quantity demanded, and prices fall.
• Excess demand – a shortage, the quantity demanded is greater than the quantity supplied, and prices rise.
• When quantity demanded equals quantity supplied, prices have no tendency to change .

A
B
S
0
Excess demand
$2.50
2.25
0
D
0
D
1
8 9 10
Quantity of DVDs (per week)

$2.50
2.25
0
B
C
S
1
S
0
Excess demand
A
D
0
8 9 10
Quantity of DVDs (per week)

• Shifts in either supply or demand change equilibrium price.
• An increase in demand or a decrease in supply:
– Creates excess demand at the original equilibrium price.
– Excess demand increases price until a new higher equilibrium price and quantity are reached.

• It has been reported that eating red meat is bad for your health. Using supply and demand curves, demonstrate the report’s likely effect on the equilibrium price and quantity of steak sold in the market.

• Why does the price of airline tickets rise during the summer months? Demonstrate your answer with demand and supply curves.

• Show how the equilibrium price and quantity will be affected by each of the following factors: a. Bad weather wreaks havoc with the tea crop b. A technological innovation lowers the cost of producing tea c.
Consumers’ income falls.( Assume tea is a normal good.) d. A medical report implying tea is bad for your health is published

• A change in quantity demanded (supplied), caused only by a change in the good’s own price, is a movement along the demand
(supply) curve.
• A change in demand (supply) is a shift of the entire demand (supply) curve.
• Factors that affect supply and demand other than price are called shift factors.

Shift Factors of Demand
Income
Prices of Other Goods
Tastes
Expectations
Taxes and Subsidies on
Consumers
Shift Factors of Supply
Price of Inputs
Technology
Expectations
Taxes and Subsidies on
Producers

• A market demand (supply) curve is the horizontal sum of all individual demand (supply) curves.
• When quantity demanded equals quantity supplied at equilibrium, prices have no tendency to change.
• When quantity demanded > quantity supplied, prices tend to rise.
• When quantity supplied > quantity demanded, prices tend to fall.

• When the demand curve shifts to the right (left), equilibrium price rises
(declines) and equilibrium quantity rises
(falls).
• When the supply curve shifts to the right
(left), equilibrium price declines (rises) and equilibrium quantity rises (falls).