distinction between the shift in the demand or supply curve and the movement along these curves

Demand and Supply Curves

Movement Along a Curve vs Shift of a Curve

When we talk about movement along a curve, we mean a change in the quantity bought or sold that happens because the price changes while everything else stays the same. Think of a line of people waiting for a concert ticket: if the ticket price goes up, fewer people will buy tickets, so the quantity demanded moves down the demand curve.

A shift of the curve happens when something other than price changes. This could be a change in income, tastes, prices of related goods, or expectations. A shift moves the entire curve left or right, changing the quantity demanded or supplied at every price.

  • 📈 Movement along the demand curve – price changes, quantity demanded changes.

  • 📉 Shift of the demand curve – non‑price factor changes, entire curve moves.

  • 🔄 Same for supply: price changes → movement along supply curve; non‑price factor changes → shift of supply curve.

Key Equations

EquationWhat It Means
\$Q_d = a - bP\$Linear demand: as price \$P\$ rises, quantity demanded \$Q_d\$ falls.
\$Q_s = c + dP\$Linear supply: as price \$P\$ rises, quantity supplied \$Q_s\$ rises.

Analogy: The Coffee Shop

Imagine a coffee shop that sells mugs of coffee.

  1. Price of a mug goes from \$3 to \$5 → fewer customers buy → movement down the demand curve.

  2. New advertisement makes coffee taste “trendy” → more people want coffee at every price → demand curve shifts right.

  3. Cost of beans rises → coffee becomes more expensive to make → supply curve shifts left.

Exam Tip Box

🔍 Remember:

  • Identify the cause (price vs non‑price).

  • Label the direction of the shift (right = increase, left = decrease).

  • Use the correct symbol: ↑ for increase, ↓ for decrease.

Quick Practice

Given the following scenario, decide whether it is a movement or a shift and indicate the direction.

  • Price of smartphones drops from \$800 to \$600.

  • Government introduces a tax on sugary drinks.

  • A new smartphone model is released with better features.

  • Consumers’ income rises significantly.

Answers:

1️⃣ Movement along the demand curve (↓ quantity demanded).

2️⃣ Shift of the supply curve (left).

3️⃣ Shift of the demand curve (right).

4️⃣ Shift of the demand curve (right).