Title: Supply, Demand, and Equilibrium
1Supply, Demand, and Equilibrium
- Today An introduction to supply and demand, and
how they relate to equilibrium
2Who is very hungry and likes bananas?
- All the bananas you care to eat for one person
(up to however many I have) - NOT extra credit, since you get free bananas
- You are eating bananas at your own risk
- You are not allowed to share bananas with anyone
else - Please report to me how many bananas you eat in
about 40 minutes
3Previously
- The 7 Core Principles
- Thinking like an economist
- Marginal cost and benefit
- Working with graphs
4Today Markets
- Supply, demand, and equilibrium
- What causes shifts in supply and demand?
- What happens when supply and/or demand shifts?
5Central organization versus Markets
- Central economic organization is rare today
- Most economic activity today occurs in markets
- Markets do fail sometimes, but this is the focus
of other chapters (e.g. Chapters 8 and 10)
6Markets
- Markets consist of buyers and sellers
- Assume many buyers and many sellers
- Fractional amounts of goods can be produced
- We will talk about supply and demand for most
markets - Exceptions will be dealt with accordingly as we
get to them
7Core principle related to demand
- Cost-benefit analysis
- Recall energy drinks example
- Think reservation price when you think
willingness to pay (WTP)
8Demand
- Demand states how much of a good that buyers are
willing to purchase given each price - Demand is typically shown on a graph, but it is
occasionally displayed on a table
9Demand
- A fundamental characteristic of demand is that as
the price of a good increases, demand typically
goes down (all else constant) - Recall that WTP for energy drinks decreases as
you consume more - Thus, each demand curve is downward sloping if we
graphed it - By convention, quantity is on the horizontal axis
and price on the vertical axis
10Core principles related to supply
- Increasing opportunity cost
- We want to produce at the lowest cost for each
additional unit - Also called low-hanging-fruit principle
- Incentive principle
- Businesses will supply less when some units are
not profitable - Businesses will supply more when producing more
could lead to higher profits
11Supply
- Supply states how much of a good that sellers are
willing to sell given each price - Similar to demand, supply is typically shown on a
graph
12Supply
- Low-cost sellers typically enter a market before
high-cost sellers - Thus, we would expect that the sellers with
lowest cost to sell a particular good - Supply is then assumed to be upward sloping
13Discrete versus continuous
- Although many products can only be purchased in
discrete amounts, we usually assume continuous
curves - Why? (Come to class to find out)
- In this class, most common curve used is linear
- We will typically ignore the discreteness
problem in supply/demand analysis
14Graphing supply and demand
15Equilibrium principle
- Another core principle
- No cash on the table ? stable
- Nobody can be made better off by changing her/his
decision - Does not address potential actions that groups of
people can make - Later topic, especially with market failure
16Equilibrium 4 units purchased, at a price of 6
17Why is a price of 6 equilibrium?
- To show that 6 is the equilibrium price, we will
show that prices above and below are not in
equilibrium - We will prove by contradiction that this price
could not be equilibrium - Suppose that a price (P) of 4 is equilibrium
18At P 4 Quantity demanded is 6, quantity
supplied is 3.33
19At P 4 Quantity demanded is 6, quantity
supplied is 3.33
- When P is 4, people are demanding a quantity that
is higher than what is supplied - Is this an equilibrium?
- No, this is not stable
- Someone can increase their production slightly,
and sell at a price of 5 to make more profits
20Now suppose that P 9 is an equilibrium
21Now suppose that P 9 is an equilibrium
- Quantity supplied is 6
- Quantity demanded is 1
- This is not stable either
- Someone not selling their entire stock can sell
for P 7 to make more money
22A change in supply versus a movement along the
supply curve
- A change in supply leads to a shift of the entire
supply curve - A movement along the supply curve can occur when
the supply curve does not move - Movement occurs when there is a change in price
- Similar ideas apply for changes in demand versus
a movement along demand curves
23What causes shifts in demand?
- Price changes of complements and substitutes
- Example of complements baseballs and baseball
bats - Example of substitutes two different brands of
cola
24What causes shifts in demand?
- Income changes
- Most goods are normal goods, meaning that when
income increases, the demand curve shifts to the
right - Some goods are inferior, meaning that when income
increases, the demand curve shifts to the left - Changes in preferences, population, and expected
future prices
25What is happening here?
26What is happening here?
- The demand curve shifts to the right
- There is a movement along the supply curve, since
supply does not change
27What is happening here?
- Note that at any price, a higher quantity is
demanded on curve D2 than on D1 - The new equilibrium price (P) and quantity (Q)
are higher when demand shifts from D1 to D2
28What causes shifts in supply?
- Anything that changes the cost of production
- If the cost of production decreases, supply
shifts to the right - If the cost of production increases, supply
shifts to the left - A change in number of suppliers
- Expectations of future prices
29What happens when both supply and demand shift?
- An example Both supply and demand shift right
30Shift in supply
- causes Q to increase and P to decrease
- Movement from A to B
A
B
31Shift in demand
- causes Q to increase and P to increase
- Movement from B to C
C
B
32What can we conclusively say about changes in Q
and P?
- Change in supply causes Q to increase and P to
decrease - Change in demand causes Q to increase and P to
increase - The only conclusion when both supply and demand
shift right is that Q increases
33Now that we have talked about supply and demand
- lets talk about bananas
- How many bananas did our volunteer eat today?
- Why not any more?
- We will talk about what happened here on Monday
34Summary
- The intersection of demand and supply curves
determines equilibrium - Equilibrium is stable
- Change in S or D causes the curve to shift
- A movement along the supply curve can occur when
the supply curve does not move - Same with demand
- Both supply and demand can shift, but be careful
of your conclusions