Year 9 Economics & Business · Economics and Business · 10m read

Markets and How They Work

Ever wonder why coffee costs more on a cold morning or why concert tickets spike right before the show? Markets are the invisible systems that decide what gets made, who gets it, and at what price—all through the simple balance of what people want (demand) versus what's available (supply). Learning how this works helps you make smarter purchasing decisions and understand everything from job markets to housing prices in your own life.

Learning objective: Explain how markets allocate resources through supply and demand.

By the end of this lesson you can:

• I can explain what a market is and why they exist.
• I can describe the laws of demand and supply.
• I can explain what happens when markets are in or out of equilibrium.

A market is a giant auction. Buyers bid, sellers ask, and prices settle where they meet. When everyone wants concert tickets, prices rise; when no one does, they fall.

Supply, demand and price

MARKET: A place (physical or digital) where buyers and sellers interact to exchange goods and services.

LAW OF DEMAND:
• As price RISES, quantity demanded FALLS (inverse relationship).
• Reasons: Substitution effect (cheaper alternatives), income effect (less real income).
• DEMAND CURVE: slopes downward.

DEMAND SHIFTERS (non-price factors):
• Income changes, tastes/preferences, price of related goods, expectations.

LAW OF SUPPLY:
• As price RISES, quantity supplied RISES (direct relationship).
• Reason: Higher prices = higher profits = more incentive to produce.
• SUPPLY CURVE: slopes upward.

SUPPLY SHIFTERS:
• Input costs, technology, number of sellers, government policy.

EQUILIBRIUM:
• Where quantity demanded = quantity supplied — the "market-clearing price."
• SURPLUS: price too high → supply exceeds demand → price falls.
• SHORTAGE: price too low → demand exceeds supply → price rises.

REAL-WORLD EXAMPLE:
• COVID-19 mask shortage (2020): demand surged + supply constrained → price spiked.
• As production increased and demand stabilised → price fell toward equilibrium.

AARI TIP: Ask Aari to explain what happens to house prices when interest rates rise.

Demand and supply rules

• Price up → demand down: Inverse relationship — law of demand.
• Price up → supply up: Direct relationship — law of supply.
• Equilibrium: Where the two curves cross — market clears.

Quick reference

| Change | Effect on price |
|---|---|
| Demand ↑ | Price ↑ |
| Demand ↓ | Price ↓ |
| Supply ↑ | Price ↓ |
| Supply ↓ | Price ↑ |
| Equilibrium | Where supply = demand |

Worked example (Medium)

A drought reduces wheat production. What happens to the price and quantity of bread?

1. Input effect. Wheat is an input for bread. Drought reduces wheat supply.
2. Supply shift. Less wheat → bread supply decreases (supply curve shifts left).
3. Price effect. At existing prices, shortage of bread → price rises.
4. Quantity effect. Higher price reduces quantity demanded → new equilibrium at higher price, lower quantity.

Answer: Bread price rises and quantity sold falls — a negative supply shock works through the market to affect consumers.

Worked example (Hard)

During COVID-19 (2020-21), the housing market experienced a price boom despite a recession. Use supply and demand analysis to explain this seemingly contradictory outcome.

1. Demand factors. The RBA cut interest rates to a record low of 0.10%, making mortgage borrowing extremely cheap. Government stimulus (HomeBuilder grants, JobKeeper) boosted household income and confidence. Remote work increased demand for larger homes and regional properties.
2. Supply factors. Construction was disrupted by lockdowns, reducing new housing supply. Existing homeowners were less likely to sell during uncertainty, reducing listings. Supply curve shifted left while demand shifted right.
3. Combined effect. Demand increased dramatically (rightward shift) while supply contracted (leftward shift). Both shifts push the equilibrium price upward. Australian house prices rose ~25% nationally in 2021.
4. Why this seems contradictory. Normally, a recession reduces demand and prices fall. But the housing market was driven by interest rates and government policy, not general economic conditions. This shows that specific market conditions can override broader economic trends.

Answer: The COVID housing boom illustrates that supply and demand shifts can produce unexpected outcomes — record-low interest rates and constrained supply outweighed recessionary pressures, driving prices sharply higher.

Common mistakes

• Confusing a movement ALONG a curve with a SHIFT of the curve. A price change causes movement along the existing curve (quantity changes). A non-price factor (income, technology, input costs) shifts the entire curve to a new position. Fix: Ask: "Is the change caused by price? → movement along the curve. Is it caused by something else? → the whole curve shifts."
• Saying "supply and demand both increase" without specifying the effect on price. If both curves shift right, quantity definitely increases but the effect on price depends on which shift is larger — the answer is ambiguous without more information. Fix: When both curves shift, state: "Quantity will [increase/decrease], but the effect on price depends on the relative size of the supply and demand shifts."
• Forgetting to state the NEW equilibrium after a shift. Describing the shift alone is incomplete. You must explain the new equilibrium — what happens to both price AND quantity. Fix: Always conclude with: "The new equilibrium is at a [higher/lower] price and [higher/lower] quantity than before the shift."

Price Elasticity — Why Some Markets React More Than Others

Not all markets respond to price changes in the same way. Price elasticity of demand measures how sensitive consumers are to price changes — and it explains why petrol prices can spike without people driving much less, while a small price increase for a particular brand of cereal can cause a big drop in sales.

Elastic demand (elasticity > 1): A small price change causes a large change in quantity demanded. This happens when:
- Many substitutes are available (different cereal brands)
- The good is a luxury, not a necessity
- Consumers have time to adjust their behaviour

Inelastic demand (elasticity < 1): Price changes have little effect on quantity demanded. This happens when:
- Few substitutes exist (petrol, insulin)
- The good is a necessity
- The good is a small portion of income (salt)
- Consumers are locked in (phone contracts)

Why this matters for policy: Taxes on inelastic goods (cigarettes, petrol) raise revenue because consumers keep buying despite higher prices — but they also hit lower-income households harder. Taxes on elastic goods change behaviour more effectively but raise less revenue.

Real-world example: Australia's tobacco excise has been highly effective — cigarette prices have roughly tripled since 2010, and smoking rates have fallen significantly. But demand for cigarettes is more elastic than for most addictive substances because substitutes (nicotine patches, vaping) are available.

Practice questions

1. According to the law of demand, when price rises:

   1. Quantity demanded rises.
   2. Quantity demanded falls.
   3. Supply falls.
   4. Equilibrium is maintained.

   (1 marks)

2. Explain what a "market surplus" is and how it corrects itself.

   (3 marks)

Summary

• Explain what a market is and why they exist.
• Describe the laws of demand and supply.
• Explain what happens when markets are in or out of equilibrium.