Introduction to Demand
Welcome to one of the most fundamental chapters in Economics! In this section, we are exploring The Role of Markets. To understand how a market works, we first need to look at the people buying things—the consumers. This is what we call Demand.
Don't worry if this seems a bit abstract at first. Economics is just the study of how people make choices. By the end of these notes, you’ll see that the "Law of Demand" is something you interact with every single time you go shopping or browse an app for a deal!
1. What is Demand?
In Economics, demand isn't just "wanting" something. You might want a private jet, but unless you have the money to buy it, you don't have "demand" for it in the eyes of an economist.
Demand is the quantity of a good or service that consumers are willing and able to buy at a given price in a given time period. We often call this Effective Demand to emphasize that you must have the cash to back up your desire!
The Law of Demand: As the price of a product falls, the quantity demanded usually increases. There is an inverse relationship between price (\(P\)) and quantity demanded (\(Qd\)).
Analogy: Imagine your favorite chocolate bar. If the price drops to 10p, you’d probably buy five of them. If the price rises to £5.00, you’d likely buy zero. That is the Law of Demand in action!
Quick Review: The Ceteris Paribus Rule
In Economics, we use the term Ceteris Paribus, which is Latin for "all other things being equal." When we say demand increases because the price fell, we are assuming that nothing else changed (like your income or your tastes). It’s like hitting a "pause" button on the rest of the world so we can see how one specific change affects the market.
Key Takeaway: Demand = Willingness + Ability to pay. Usually, lower prices lead to higher demand.
2. Individual vs. Market Demand
Markets are made up of many different people. To understand the whole market, we just add everyone together.
- Individual Demand: The demand of just one person (e.g., how many coffees you buy at £3.00).
- Market Demand: The total demand from all consumers in the market for a particular good.
Step-by-Step Calculation: If at £2.00, Student A wants 3 apples and Student B wants 5 apples, the Market Demand at £2.00 is \(3 + 5 = 8\) apples.
3. Movements vs. Shifts (The Golden Rule)
This is the part where many students get tripped up, but here is a simple trick to remember it: Price stays on the path!
Movements Along the Curve
A movement only happens when the price of the good itself changes. This causes a change in the quantity demanded.
- Extension of Demand: A movement down the curve caused by a fall in price (Quantity increases).
- Contraction of Demand: A movement up the curve caused by a rise in price (Quantity decreases).
Shifts of the Curve
A shift happens when anything other than price changes. This changes the Demand (the whole curve moves).
- Shift to the Right: An increase in demand (people want more at every price).
- Shift to the Left: A decrease in demand (people want less at every price).
Memory Aid:
Increase = Right (Both start with a vowel-sound 'I' and 'R'... okay, maybe just remember Left is Less, Right is More!)
Key Takeaway: Price change = Movement. Non-price change = Shift.
4. Why does Demand Shift? (The Factors)
Why would people suddenly want more of something even if the price hasn't changed? We use the mnemonic PASIFIC to remember the main reasons:
- P - Population: More people in the country means more mouths to feed and more demand for everything.
- A - Advertising: A successful ad campaign makes a product "cooler," shifting demand to the right.
- S - Substitutes: If the price of Pepsi goes up, the demand for Coca-Cola shifts to the right (people switch).
- I - Income: For normal goods, when people earn more, they buy more. (For inferior goods like "value" noodles, demand actually drops when income rises!).
- F - Fashion and Tastes: If it's "in," demand shifts right. If it's "out," it shifts left.
- I - Interest Rates: If interest rates are low, it's cheaper to borrow money to buy expensive things like cars, so demand shifts right.
- C - Complements: These are goods bought together (like printers and ink). If the price of printers drops, the demand for ink shifts to the right.
Common Mistake to Avoid: Never say "Price causes a shift." If the price of a burger changes, we move along the burger demand curve. If the price of chicken changes, it might shift the demand for burgers (because they are substitutes).
5. Joint, Competitive, and Composite Demand
Goods are often related to each other. OCR wants you to know these three specific types:
Competitive Demand (Substitutes)
This occurs when goods are in competition. You buy one or the other.
Example: iPhone vs. Samsung Galaxy. If the price of iPhones rises, the demand for Samsung rises.
Joint Demand (Complements)
This occurs when goods are bought together.
Example: Razors and razor blades. If you buy more razors, you'll naturally need more blades.
Composite Demand
This is when a good has more than one use.
Example: Milk. It is demanded by people who want to drink it, people who make cheese, and people who make yogurt. If the demand for cheese goes up, there is less milk available for drinking!
Key Takeaway: Markets are interconnected. A change in one market often causes a shift in another.
6. The Concept of the Margin and Utility
Why is the demand curve downward sloping? Why don't we just keep buying things forever?
Utility is a fancy word for "satisfaction" or "happiness."
Marginal Utility is the extra satisfaction you get from consuming one more unit of a good.
The Law of Diminishing Marginal Utility: As you consume more of a good, the extra satisfaction you get from each additional unit falls.
Example: The first slice of pizza when you are starving is amazing (High Utility). The fifth slice is okay. The tenth slice might actually make you feel sick (Negative Utility).
Connection to Demand: Because each extra unit gives you less satisfaction, you are only willing to buy more if the price falls. This is why the demand curve slopes downwards!
Quick Review Box
Demand Basics:
1. Price goes up \(\uparrow\), Quantity Demanded goes down \(\downarrow\).
2. Movements are caused by Price.
3. Shifts are caused by Non-Price factors (PASIFIC).
4. Diminishing Marginal Utility explains why the curve slopes down.
Summary: Putting it All Together
Demand is the "consumer side" of the market. It shows how much we want and can afford. While price is the main thing that dictates how much we buy (movement), our choices are also influenced by our bank balances, our friends' opinions, and the prices of related goods (shifts). Understanding these patterns allows economists to predict how markets will react to changes in the real world.