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
| Equation | What 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.
- Price of a mug goes from $3 to $5 → fewer customers buy → movement down the demand curve.
- New advertisement makes coffee taste “trendy” → more people want coffee at every price → demand curve shifts right.
- 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).
Revision
Log in to practice.