Elasticity of supply

Welcome to the World of Supply!

In the previous chapters, we looked at how consumers react to price changes (Demand). Now, we are switching sides! We are going to look at the producers—the businesses that make and sell products.

Price Elasticity of Supply (PES) is all about how "stretchy" a business is. If the price of a product goes up, does the business sprint to produce more, or are they stuck at their current level? Understanding this helps us predict how markets react to changes in the real world. Don't worry if it sounds a bit technical; we’ll break it down step-by-step!

1. What is Price Elasticity of Supply (PES)?

Price Elasticity of Supply measures the responsiveness of the quantity supplied of a good to a change in its price.

Think of it like this: If the price of a fidget spinner doubles, can the factory suddenly make twice as many? If yes, their supply is elastic (stretchy). If they can’t make any more because they’ve run out of plastic, their supply is inelastic (stiff).

The Formula

To find the exact number for PES, we use this formula:
\( PES = \frac{\% \text{ change in quantity supplied}}{\% \text{ change in price}} \)

Top Tip for Memory: Just like with demand, the Quantity is always on Top (Q before P in the alphabet).

Example: If the price of smartphones rises by 10% and the quantity supplied increases by 20%:
\( PES = \frac{+20\%}{+10\%} = 2 \)

Quick Review: Unlike Demand (which is usually negative), PES is almost always positive. This is because of the Law of Supply: as price goes up, firms want to supply more to make more profit!

2. Interpreting the Numbers

What does the result of your calculation actually mean? Here is the cheat sheet:

PES > 1: Elastic Supply
The percentage change in quantity is bigger than the change in price. The firm is very responsive.
Analogy: A pizza shop. If prices go up, they can easily stay open an extra hour or buy more dough to make more pizzas.

PES < 1: Inelastic Supply
The percentage change in quantity is smaller than the change in price. The firm finds it hard to change production levels quickly.
Example: Farming. If the price of wheat shoots up today, a farmer can't just make wheat grow faster. They have to wait for the next harvest.

PES = 0: Perfectly Inelastic
Quantity supplied doesn't change at all, no matter the price. On a graph, this is a vertical line.
Example: Seats in a football stadium for a specific match. Even if tickets go up to £10,000, you can't magically add more seats to the stadium that day!

PES = \(\infty\) (Infinity): Perfectly Elastic
At a specific price, supply is infinite, but if the price drops even a tiny bit, supply falls to zero. This is a horizontal line.

PES = 1: Unitary Elasticity
The percentage change in price and quantity are exactly the same.

Key Takeaway: The "flatter" the supply curve, the more elastic it is. The "steeper" the curve, the more inelastic it is.

3. Factors that Influence PES

Why are some businesses "stretchier" than others? You can remember the main factors using the mnemonic "S.S.S.T.":

1. Spare Capacity
Is the factory running at 100%? If a factory is only using half its machines, it has "spare capacity" and can easily increase supply if prices rise. This makes supply elastic.

2. Stocks (Inventories)
Can the product be stored? If a business has a warehouse full of finished goods (like canned soup), they can react to a price rise instantly by shipping out the boxes. This makes supply elastic. Fresh strawberries, however, rot quickly—you can't keep huge stocks, making supply more inelastic.

3. Substitutability of Factors
Can the business switch its resources easily? If a factory can switch from making blue pens to black pens instantly, the supply of black pens is elastic. If it requires specialized, rare machinery that takes years to build, supply is inelastic.

4. Time Period
This is the most important one for your exams!
- Short Run: At least one factor of production (like the size of the factory) is fixed. It’s hard to change supply quickly, so PES is usually inelastic.
- Long Run: All factors of production can be changed. You can build new factories and hire more staff. Therefore, supply is much more elastic in the long run.

Did you know? In the "momentary period" (the immediate market period), supply is almost always perfectly inelastic because there is literally no time to change production!

4. Common Mistakes to Avoid

Mistake 1: Confusing PES with PED.
Remember, PES is about the producer's ability to change production. PED is about the consumer's desire to buy.

Mistake 2: Forgetting the units.
When calculating, always use the percentage change, not just the change in price/quantity.

Mistake 3: Thinking PES is negative.
Supply curves go up (Positive correlation). If your PES calculation is negative, you’ve likely used a demand figure by mistake!

Summary: The Quick Review Box

- Definition: How much quantity supplied changes when price changes.
- Formula: % Change in Qs / % Change in P.
- Elastic (>1): Producers can respond easily (e.g., they have spare capacity or stocks).
- Inelastic (<1): Producers struggle to respond (e.g., they have no stocks or it's the short run).
- Long Run: Supply is always more elastic because firms have time to expand.

Don't worry if this seems tricky at first! Just remember that PES is simply a measure of how "ready" a business is to chase higher prices by making more stuff. The easier it is for them to make more, the higher the PES!