Notes: Market Equilibrium & Shifts

Demand and Supply Fundamentals

Demand curve: downward-sloping; as price falls, quantity demanded typically rises.
Supply curve: upward-sloping; as price rises, quantity supplied typically rises.
Equilibrium (price and quantity): the point where demand and supply meet. Geometrically, this is where the two curves intersect.
At equilibrium, the market clears: the quantity supplied equals the quantity demanded. Denote this as Q^ and the corresponding price as P^, so the condition is Qd(P^) = Qs(P^).
In the example discussed, the setup is a simple diagram with a downward-sloping demand curve and an upward-sloping supply curve. The intersection represents the equilibrium price and quantity.

Shortage situation occurs when the market price is below the equilibrium price, causing quantity demanded to exceed quantity supplied.
Numerical illustration from the transcript: at price P = 13.75, the quantities are:
- Quantity supplied: Q_s = 900
- Quantity demanded: Q_d = 1300
- Shortage amount: S = Qd - Qs = 1300 - 900 = 400
This mismatch creates a shortage because there are too many buyers relative to the goods available.
Underground takeaway: a shortage happens when the market price is too low to clear the market; conversely, a price above equilibrium creates a surplus.
Conceptual takeaway: in a perfectly functioning free market, shortages or surpluses signal the need for price adjustments toward equilibrium.

Chapter four preview: government intervention in a free market can introduce inefficiencies like shortages or surpluses by distorting the price mechanism.
Interventions discussed include actions that fix or cap prices, which can obstruct market-clearing adjustments.
Key implication: when the market is functioning normally, interventions tend to create distortions (e.g., persistent shortages or surpluses) rather than solve underlying allocation problems.
Practical takeaway: understanding the equilibrium framework helps explain why price controls can have unintended consequences.

When a factor causes the demand curve to shift, equilibrium quantity and price respond depending on the direction and magnitude of shifts.
Directional intuition from the transcript:
- If demand increases (demand curve shifts right), the quantity traded tends to rise. The price tends to rise as well, but the exact change depends on how supply responds.
- If supply shifts (e.g., supply increases, curve shifts right), this tends to increase quantity and may lower price if the supply increase dominates.
Scenario analysis from the transcript:
- Case with increasing supply (rightward shift of supply) and increasing quantity: the interaction with demand determines the net price effect.
- Case with decreasing supply (leftward shift) and decreasing demand: quantity falls, but the price effect is ambiguous unless you know the magnitudes; if demand falls more than supply, price can fall or rise depending on which effect dominates.
- If both demand and supply move but in opposite directions, the direction of the price change depends on which curve shifts more in magnitude.
General rule: the new equilibrium is found where the new curves intersect, i.e., where Qd^{new}(P) = Qs^{new}(P). The resulting equilibrium price is P^{new} and quantity is Q^{new}.
Notation to remember:
- Original equilibrium: P^, Q^ where Qd(P^) = Qs(P^).
- Shifts produce new equilibrium points: P^{new}, Q^{new} subject to new intersection of the shifted curves.

Example: Maryville housing context — houses and apartments are substitutes.
- Substitutes: if the price of one good rises, demand for the substitute tends to increase.
- The transcript frames this as a type of real-world question similar to those in practice problems (e.g., Achieve questions).
Takeaway from substitutes discussion:
- Substitutes influence the slope and position of the demand curve for each good because consumer choices shift between alternatives as relative prices change.
- Understanding substitution helps explain why a small change in price can lead to a larger-than-expected change in quantity demanded for related goods.

Core link: price signals coordinate supply and demand; prices adjust to balance quantity supplied and demanded.
Market failures: when government intervention distorts prices, the natural adjustment flow can be slowed or reversed, creating inefficiencies.
Real-world relevance: shortages and surpluses show up in markets when regulation, taxes, or price controls interact with supply and demand dynamics.
Foundational principle: the equilibrium framework underpins microeconomic analysis of markets, enabling predictions about how shocks or policy changes propagate through price and quantity.

Demand and supply curves intersect at equilibrium: Qd(P^) = Qs(P^), with equilibrium price P^ and equilibrium quantity Q^.
Shortage when price is too low: if P < P^*, then Qd(P) > Qs(P), leading to shortage S = Qd(P) - Qs(P) > 0.
Specific numerical example from transcript:
- Price: P = 13.75
- Quantity supplied: Q_s = 900
- Quantity demanded: Q_d = 1300
- Shortage: S = Qd - Qs = 1300 - 900 = 400
If the market shifts to a new equilibrium with shifted curves, the new equilibrium must satisfy: Qd^{new}(P^{new}) = Qs^{new}(P^{new}), yielding new values P^{new} and Q^{new}.
Economic intuition: when both demand and supply change, the price and quantity outcomes depend on the relative magnitudes of the shifts; no single direction can be asserted without the specific data of the shifts.

Practice pricing scenarios by calculating shortages or surpluses from given price, Qd, and Qs values.
When given shifts, diagram both curves to visualize how equilibrium moves; label new intersection points with P^{new} and Q^{new}.
Remember the policy implications: price controls can prevent markets from clearing, leading to persistent distortions.
Use substitution concepts to reason about demand for related goods when one good’s price changes.
Try to reproduce the logic from Achieve-type questions to strengthen intuition for shifts and equilibrium changes.

Equilibrium is where Qd(P^) = Qs(P^), with equilibrium price P^ and quantity Q^.
Shortages occur when price is below equilibrium; example: at P = 13.75, Qd = 1300, Qs = 900, shortage = 400.
Government intervention can induce shortages or surpluses by distorting price signals.
Shifts in demand and/or supply determine new equilibrium; the direction of price change depends on relative magnitudes of the shifts.
Substitutes affect demand curves and consumer choices; practical questions in exam prep emphasize applying these concepts to real-world scenarios.