Supply, Demand, Shifts, and Price Controls

Objectives

• Students will be able to draw a correctly labeled supply-and-demand graph and identify equilibrium price and quantity.
• Students will be able to distinguish a shift of a curve from a movement along it and name the determinant that caused a given shift.
• Students will be able to predict the effect on equilibrium price and quantity of a single shift, and identify which variable is indeterminate when both curves shift.
• Students will be able to draw a binding price ceiling and a binding price floor and label the resulting shortage or surplus.

Materials (all free, no student accounts needed)

• Supply and Demand module lesson
• Supply and Demand sandbox graph
• Draw-the-graph FRQ practice
• Trace-the-shock walkthroughs
• Supply and Demand practice set

Five-minute warm-up, no prep

Open one of these on the projector. Students say what they think happens to price and quantity before anything moves, lock it in, and then the graph plays out step by step. No accounts, nothing graded or stored.

• Tea Gets Pricier
• Coffee Beans Get Expensive
• Printers Get Pricier, Ink Suffers

Warm-up (10 min)

• Do Now: "Gas stations near a stadium raise prices before a big game. Did the demand curve move, or did buyers move along it? Defend your answer in one sentence."
• Cold-call two students with opposite answers, then hold the vote. Do not resolve it yet; tell them this lesson settles it and come back to it before the exit ticket.

Direct instruction (40 min)

• Project the Core Model and Equilibrium sections of the module lesson. Draw demand and supply, label axes (Price and Quantity), and mark equilibrium where they cross.
• Build the two shifter lists on the board. Demand: tastes, income (normal vs inferior), prices of related goods, expectations, number of buyers. Supply: input costs, technology, taxes and subsidies, expectations, number of sellers.
• Hammer the rule that separates shifts from movements: a change in the good's OWN price is always a movement along the curve; anything else shifts it.
• Work one single-shift case fully (a substitute's price rises, demand shifts right, price up and quantity up). Then work a double shift (demand right, supply right) and show that quantity is determinate but price is indeterminate.
• Introduce price controls: a binding ceiling sits BELOW equilibrium and creates a shortage; a binding floor sits ABOVE equilibrium and creates a surplus. Draw both and shade the gap.

Guided practice (50 min)

• Project /sandbox/supply-demand. Read a scenario aloud ("a health study links soda to disease") and have a student come drag the correct curve. Cold-call another student to name the exact determinant before revealing the new equilibrium.
• Run these four scenarios back to back, alternating who drags and who names the determinant. (1) A spring frost destroys part of the orange crop: supply of oranges shifts left, price up and quantity down, the determinant is a resource/input shock. (2) Average incomes rise and dining out is a normal good: demand for restaurant meals shifts right, price up and quantity up, the determinant is income. (3) A new automated loom cuts the cost of weaving cloth: supply of cloth shifts right, price down and quantity up, the determinant is technology. (4) The price of beef, a substitute for chicken, falls: demand for chicken shifts left, price down and quantity down, the determinant is the price of a related good. After each, cold-call: "Own-price change or a shifter? Movement along or a shift?"
• For the double-shift case, open a Trace-the-Shock walkthrough from /graph-walkthroughs (the both-curves-shift laptop scenario) and step through it, pausing so students predict which variable goes indeterminate before the next step.
• Switch to price controls in the sandbox: drag the price line below equilibrium and cold-call a student to point to the shortage, then above equilibrium for the surplus. Have the class label quantity demanded and quantity supplied at the controlled price.
• Assign a /frq-practice/draw shift scenario for pairs to attempt on their own screens or on the projected copy, then debrief the labeling.

Independent practice (40 min)

• Students work through the Supply and Demand practice set, starting with the shift-identification and price-control items.
• Each student draws two graphs by hand from written prompts: one single shift with the equilibrium arrows labeled, and one binding price ceiling with the shortage marked.

Exit ticket

• A new technology lowers the cost of making laptops at the same time incomes rise. Draw the graph and state what happens to equilibrium price and quantity, naming which one is indeterminate.
• The government sets a price of $2 on a good whose equilibrium price is $5. Is this a ceiling or a floor, is it binding, and does it cause a shortage or a surplus?
• Back to the Do Now: the stadium gas price. Shift or movement along? Explain in one sentence.

Homework

• Finish the Supply and Demand practice set and flag the two questions you were least sure about.
• Attempt one draw-the-graph FRQ shift scenario at /frq-practice/draw and screenshot or sketch your labeled result to submit.

Differentiation

• Early finishers: ask them to construct a scenario for each of the four determinate/indeterminate combinations of a double shift and draw the graph for each.
• Support: provide a half-sheet with pre-labeled axes and a word bank of the determinants so students spend their effort on the direction of the shift, not the setup.
• Reteach group: pull students who missed the shift-vs-movement exit item and run three rapid own-price-vs-shifter cards before the next class starts.

Misconceptions to head off

• Belief: a change in the good's own price shifts the demand curve. Correction: an own-price change is a movement along the curve; only non-price determinants shift it.
• Belief: when both curves shift, price and quantity both move in a knowable direction. Correction: one of the two is always indeterminate without more information about the size of each shift.
• Belief: a price ceiling raises the price and a price floor lowers it. Correction: a binding ceiling sits below equilibrium and causes a shortage; a binding floor sits above equilibrium and causes a surplus.
• Belief: higher demand causes higher supply. Correction: the curves are independent; a demand increase is a movement along supply (a change in quantity supplied), not a shift of supply.