Law of Supply - Comprehensive Study Notes

The Law of Supply

  • Definition: A principle in economics stating that as the price of a good, service, or resource rises, the quantity supplied will increase, and as price falls, the quantity supplied will decrease, all else held constant (ceteris paribus).
  • Formal relation: the quantity supplied $Qs$ is positively related to price $P$; direction of change is such that rac{dQs}{dP} > 0.
  • Key takeaway: Higher prices incentivize producers to offer more of a good or service for sale.

Supply Schedule and Curve

  • Supply schedule: A table showing the relationship between price and quantity supplied.
  • Illustrative data from the transcript (demonstrates a positive relationship):
    • (P, Q_s) = (400, 2000),
      (325, 1750),
      (250, 1500),
      (175, 1250),
      (100, 1000)
  • Interpretation: As price decreases, quantity supplied decreases; as price increases, quantity supplied increases.
  • Supply curve: The graphical representation of the supply schedule; upward-sloping in standard models due to the positive relationship between price and quantity supplied.
  • Additional axis context (from the slide): Price axis and Quantity axis showing typical ranges, reinforcing the upward slope of the curve.

Movement Along vs Shift in the Supply Curve

  • Movement along the supply curve:
    • Caused by a change in the price of the good itself.
    • Results in a change in quantity supplied (a movement along the existing curve).
  • Shift of the supply curve (non-price change):
    • Caused by non-price factors (see non-price changes below).
    • Results in a different quantity supplied at every price (the entire curve shifts left or right).
  • Summary: Movement along = price change; Shift = non-price change.

Non-Price Changes to Supply

  • Tax/Subsidy
    • Taxes decrease supply (shift left) because costs rise or profitability falls.
    • Subsidies increase supply (shift right) by effectively lowering costs or increasing profitability.
  • Resource Cost (Input Prices)
    • Higher input costs reduce supply (shift left).
    • Lower input costs increase supply (shift right).
  • Technology
    • Advancements reduce production costs or increase efficiency, increasing supply (shift right).
  • Future Expectations
    • If producers expect higher prices in the future, they may restrict current supply (shift left) to sell more later at higher prices.
    • If they expect lower future prices, they may increase current supply (shift right).
  • Number of Sellers
    • More sellers increase market supply (shift right).
    • Fewer sellers decrease market supply (shift left).
  • Note: These non-price changes cause the entire supply curve to shift, not just a movement along it.

In-Class Milkshake Supply Worksheet (Tasks 1–6)

  • Task 1: The price of ice cream (an input) decreases.
    • Effect on supply: Supply shifts to the right (increase in supply).
    • Reason: Lower input costs reduce production costs, making production more profitable at each price.
  • Task 2: Wages paid to milkshake makers increase.
    • Effect on supply: Supply shifts to the left (decrease in supply).
    • Reason: Higher input costs raise production costs, reducing profitability at each price.
  • Task 3: Milkshakes become so popular that the number of milkshake vendors increases.
    • Effect on supply: Supply shifts to the right (increase in supply).
    • Reason: More sellers add to market supply.
  • Task 4: Local taxes on milkshake producers increase.
    • Effect on supply: Supply shifts to the left (decrease in supply).
    • Reason: Higher taxes raise costs or reduce profitability.
  • Task 5: The price of milkshakes increases.
    • Effect on supply: Movement along the supply curve (not a shift).
    • Reason: Price change causes a change in quantity supplied but not in the overall supply curve.
  • Task 6: A new low-fat frozen yogurt has come out.
    • Effect on supply: Supply of milkshakes shifts left (decrease in supply).
    • Reason: Introduction of a substitute product diverts production, reducing milkshake supply.

Practice Questions (Test Your Knowledge)

  • Question 1: The law of supply says that
    • A) As price increases, firms supply more and quantity increases.
    • B) As price increases, firms supply less and quantity decreases.
    • C) Price has no impact on supply.
    • D) Price is the only thing that impacts supply.
    • Correct answer: A
  • Question 2: Which of the following scenarios will not cause an increase in supply?
    • A. Technology improves and drives down costs
    • B. The number of suppliers increases
    • C. The price of the product decreases
    • D. Taxes decrease
    • Correct answer: C

Review and Key Concepts

  • Law of Supply: Relationship between price and quantity supplied (positive relationship).
  • Movement Along vs Shift:
    • Movement along the supply curve = price-driven change in quantity supplied.
    • Shift in supply curve = non-price-driven change in supply.
  • Change in Quantity Supplied vs Change in Supply:
    • Change in Quantity Supplied = movement along the curve due to price change.
    • Change in Supply = shift of the entire curve due to non-price factors.
  • Tax vs Subsidy:
    • Tax reduces supply (shift left); Subsidy increases supply (shift right).
  • Non-Price Changes in Supply (examples): Tax/subsidy, resource costs, technology, future expectations, number of sellers.
  • Real-world relevance: Policies (taxes/subsidies), technology adoption, changes in input costs, and market structure (number of sellers) visibly affect supply and prices in markets.
  • Ethical/Practical implications: Government interventions (taxes, subsidies) alter incentives; technological shifts can impact employment and industry viability; consumer welfare depends on how supply responds to these factors.

Cartoon Illustration: Supply and Demand Concepts in Practice

  • Scene depicts a lemonade stand with a sole stockholder demanding high profits and an exorbitant salary, illustrating perceived profit motives in supply decisions.
  • Dialogue highlights tensions around costs (labor, materials), regulation (health and environmental rules), and market dynamics (demand signals) impacting supply decisions.
  • Key takeaways from the cartoon:
    • Supply and demand interact to determine prices and quantities.
    • Stockholders’ and firms’ decisions are influenced by costs, profits, and regulatory environment.
    • External factors (regulations, subsidies, taxes) can affect the incentives to produce.
  • Notable phrases within the cartoon include:
    • CAVEAT EMPTORIS (buyer beware) as a motto; reflects consumer-producer dynamics.
    • Discussion of subsidies, regulations, and costs as drivers of pricing and production decisions.
    • The depiction emphasizes that price signals alone do not tell the whole story; policy and costs shape supply decisions.

Connections and Takeaways for Exam Preparation

  • Always distinguish between movement along a curve (price-driven) and a shift of the curve (non-price factors).
  • Be able to identify the direction of shift given a non-price factor:
    • Rightward shift (increase in supply) vs Leftward shift (decrease in supply).
  • Know common non-price factors and their typical effects:
    • Technology improves production: shift right.
    • Higher input costs: shift left.
    • More sellers: shift right.
    • Taxes: shift left; Subsidies: shift right.
    • Expectations of future prices: depending on expectation, can shift left or right.
  • Practice with the milkshake worksheet logic: determine which factor causes a shift vs a movement along the curve.
  • Be comfortable with simple data interpretation from a supply schedule and translating it into a graph (or the concept of a graph) showing a positive slope.