A supply curve is an upward-sloping graph showing the positive relationship between a good's price and the quantity producers are willing to sell (the law of supply). Price changes move you along the curve; determinants like input prices, technology, and taxes shift the whole curve.
A supply curve plots price on the vertical axis and quantity supplied on the horizontal axis, and it slopes upward. That upward slope is the law of supply in picture form. When the price rises, producing more becomes more profitable, so producers offer more units for sale (EK MKT-2.C.1).
Here's the distinction the AP exam loves. A change in the good's own price moves you along the existing curve (a change in quantity supplied). A change in anything else, like input prices, technology, taxes or subsidies, producer expectations, or the number of sellers, shifts the entire curve left or right (EK MKT-2.D.1). Think of the curve as a producer's menu of "at this price, I'll sell this much." Price changes just point to a different line on the menu. Shifters rewrite the whole menu.
The supply curve lives in Topic 1.5 (Supply) in Unit 1: Basic Economic Concepts, supporting learning objectives 1.5.A (define the law of supply), 1.5.B (explain the price-quantity supplied relationship), and 1.5.C (explain the determinants of supply). But its real payoff comes later. Almost every graph you draw in AP Macro is some version of a supply curve meeting a demand curve. Aggregate supply, the supply of loanable funds, the supply of currency in foreign exchange markets, all of them run on the same logic you learn here. If you can't tell a shift from a movement along the curve in Unit 1, every later unit gets harder.
Keep studying AP Macroeconomics Unit DVfDhhV6MTWFJhYx
Law of Supply (Unit 1)
The law of supply is the rule, and the supply curve is the rule drawn as a picture. "Positive relationship between price and quantity supplied" is just a sentence describing an upward slope.
Market Equilibrium (Unit 1)
The supply curve is only half the story. Where it crosses the demand curve, you get the equilibrium price and quantity. Shift the supply curve and equilibrium moves in a predictable direction, which is exactly the prediction skill SAQs test.
R-O-T-T-E-N (Unit 1)
This mnemonic lists the supply shifters, things like resource (input) prices, taxes, technology, expectations, and the number of sellers. Anything on this list shifts the curve. Anything not on this list (meaning the good's own price) moves you along it.
Loanable Funds and Aggregate Supply (Units 2-4)
Macro reuses the supply curve constantly. When the 2018 SAQ on Ucheland cut taxes on interest earnings, households saved more and the supply of loanable funds shifted right. When economy-wide wages rise, short-run aggregate supply shifts left. Same shift logic, bigger stage.
Multiple-choice questions hit one distinction over and over. They give you a change and ask whether it causes a movement along the supply curve or a shift of the whole curve. A price change alone means movement along; a determinant change (like labor unions winning higher wages across industries) means the curve shifts left because production costs rose. You'll also see straight law-of-supply questions asking you to predict what happens to quantity supplied when price changes, holding everything else constant. On SAQs, supply curve logic shows up inside macro models. The 2018 SAQ on Ucheland required shifting the supply of loanable funds after a tax change, and full-employment scenarios like the 2017 SAQs lean on aggregate supply reasoning. Your job is always the same. Identify what changed, decide shift or movement, draw it correctly with labeled axes, and state the effect on equilibrium price and quantity.
A change in supply shifts the entire curve and is caused by a determinant like input prices, technology, or taxes. A change in quantity supplied is a movement along a fixed curve and is caused by one thing only, the good's own price. If an MCQ says "the price of the good rose," the curve does not move. If it says "wages rose" or "a new technology cut costs," the whole curve shifts. Mixing these up is the single most common Unit 1 error.
The supply curve slopes upward because of the law of supply, which says price and quantity supplied move in the same direction (EK MKT-2.C.1).
A change in the good's own price causes a movement along the supply curve, never a shift of it.
Determinants of supply, like input prices, technology, taxes, subsidies, expectations, and the number of sellers, shift the entire curve (EK MKT-2.D.1).
Higher production costs (like an economy-wide wage increase) shift the supply curve left, meaning less is supplied at every price.
The same shift-versus-movement logic applies to every supply curve in AP Macro, including aggregate supply and the supply of loanable funds, so master it in Unit 1.
It's an upward-sloping graph showing how much producers are willing to sell at each price. It appears in Topic 1.5 and illustrates the law of supply, the positive relationship between price and quantity supplied.
No. A change in the good's own price causes a movement along the existing curve, called a change in quantity supplied. Only determinants like input prices, technology, taxes, expectations, or the number of sellers shift the whole curve.
Supply is the entire curve, the whole relationship between price and output. Quantity supplied is one specific point on that curve at one specific price. "Increase in supply" means the curve shifted right; "increase in quantity supplied" means you moved up along it.
Higher prices make producing additional units more profitable, so producers are willing to supply more. That positive price-quantity relationship is the law of supply (EK MKT-2.C.1), and it's what gives the curve its upward slope.
Anything that raises production costs or shrinks the market, such as higher input prices (like union-negotiated wage increases), new taxes, or fewer sellers. A leftward shift means less is supplied at every price, which raises equilibrium price and lowers equilibrium quantity.