Supply & Demand
The price isn't a number someone picks. It's where two curves meet.
Prices are a conversation between how much exists and how much people want. Where the two curves cross sets the price — and shifting either one moves it in a predictable direction. The engine under every market, from coffee to housing to your own salary.
Why does a bottle of water cost a few cents in a supermarket and ten dollars in a desert? Same water. The thing that changed isn’t the water — it’s the balance between how much of it exists and how much people want it. That balance has a name, and it is the single most powerful model in all of economics: supply and demand. Master it and prices stop looking like arbitrary numbers that companies pick out of greed, and start looking like what they actually are — signals, the result of millions of strangers each chasing their own best deal.
Here’s the whole machine in one sentence. Demand describes how much people want to buy at each possible price (cheaper → they want more). Supply describes how much producers want to sell at each possible price (pricier → they make more). Draw both as curves and they cross at exactly one point — the equilibrium, the one price where the amount wanted equals the amount offered and the market clears. Nudge either curve and the crossing point slides in a direction you can predict before it happens. A frost kills the coffee harvest (supply falls) → coffee gets pricier. A diet fad makes everyone want avocados (demand rises) → avocados get pricier. You’re not memorising facts; you’re running a model.
This course builds that model from absolutely nothing — it assumes only that you know what an opportunity cost is (the value of the best thing you gave up), because the curves are secretly built out of opportunity costs. We’ll draw the two curves and learn the laws that bend them; find the equilibrium and watch what happens when the price is wrong; separate the one mistake that trips up everyone (confusing a shift of a curve with a movement along it); measure how hard quantity reacts to price (elasticity) and why that decides whether a price rise makes you richer or poorer; and finally see what happens when someone forces the price away from equilibrium with a ceiling or a floor — rent control, minimum wage, ticket scalping — and why the result is always the same shape. You’ll drag interactive curves, watch shortages open up as visible gaps, and leave able to look at any price — your rent, your wage, a plane ticket, a cup of coffee — and ask the two questions that explain it: what’s happening to supply, and what’s happening to demand?
In this topic
- 1 The Price Is Where Two Curves Meet A bottle of water costs cents in a shop and ten dollars in a desert — same water. The price isn't picked; it's where how-much-exists meets how-much-is-wanted. A tour of the whole course in one lesson. 7 min
- 2 The Two Curves Demand slopes down, supply slopes up — and both for the same reason: opportunity cost. Meet the law of demand, the law of supply, and learn to read the graph everything else in this course stands on. 10 min
- 3 Equilibrium: Where the Market Clears The two curves cross at exactly one price — the one where the amount people want equals the amount produced. Above it, a glut; below it, a queue. And a free price hunts its way back to the crossing point all on its own. 11 min
- 4 Shifts vs. Movements The mistake that trips up almost everyone: a change in the good's own price moves you ALONG a curve; a change in anything else — income, tastes, input costs, technology, a substitute's price — shifts the WHOLE curve. Get this and you can read any headline. 12 min
- 5 Elasticity: How Much Quantity Reacts Two goods can both obey the law of demand yet react completely differently to a price rise. Insulin barely budges; a fancy dinner collapses. Elasticity measures the sensitivity — and decides whether raising your price makes you richer or poorer. 12 min
- 6 Price Controls & the Signal Force a price below equilibrium and you get shortages and queues; force it above and you get gluts. Rent control, minimum wage, ticket scalping — all the same shape. And underneath it: a price is information, quietly coordinating millions of strangers. 12 min
- 7 Final Exam: Supply & Demand A graded, one-way final exam on supply and demand — the two curves and their laws, equilibrium, surplus and shortage, shifts vs. movements, the demand and supply shifters, elasticity and the revenue twist, price ceilings and floors, and price as a signal. Pass mark 70%. 22 min
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