An equilibrium exists in a market when there is no pressure for the market price to change. Learn about what it means for a market equilibrium to exist, and how to identify a market equilibrium in a market model. Created by Sal Khan.

Demand for normal goods increases when income increases, but demand for inferior goods decreases when income increases. In this video, we use the example of a computer and a car to describe the concepts of normal goods and inferior goods and show how a change in income affects the demand for each using a graph of the demand curve. Created by Sal Khan.

Positive statements are fact-based, but normative statements are based on opinions. In this video, learn about the distinction between positive statements and normative statements, and why economists emphasize positive analysis vs. normative analysis, as well as how to identify positive statements vs. normative statements.

Opportunity cost is the value of something given up to obtain something else. In this video, we explore the definition of opportunity cost, how to calculate opportunity cost, and how the PPC illustrates opportunity cost. Created by Sal Khan.

In this video, we use the PPCs for two different countries that each produce two goods in order to create an output table based on the data in the graph. We then use the output table to determine the opportunity costs of producing each good. Finally, we determine which country has a comparative advantage in each good.

A rational agent considers all costs, including explicit and implicit costs, when deciding whether or not to undertake an action. In this video, learn about how opportunity costs represent the cost of the next best alternative.

The shape of a production possibility curve (PPC) reveals important information about the opportunity cost involved in producing two goods. When the PPC is a straight line, opportunity costs are the same no matter how far you move along the curve. When the PPC is concave (bowed out), opportunity costs increase as you move along the curve. When the PPC is convex (bowed in), opportunity costs are decreasing.

Complements are goods that are consumed together. Substitutes are goods where you can consume one in place of the other. The prices of complementary or substitute goods also shift the demand curve. When the price of a good that complements a good decreases, then the quantity demanded of one increases and the demand for the other increases. When the price of a substitute good decreases, the quantity demanded for that good increases, but the demand for the good that it is being substituted for decreases. Take a deeper dive into how changes in the prices of complements and substitutes affect the demand curve in this video. Created by Sal Khan.

In this video, Sal explains how the production possibilities curve model can be used to illustrate changes in a country's actual and potential level of output. Concepts covered include efficiency, inefficiency, economic growth and contraction, and recession. When an economy is in a recession, it is operating inside the PPC. When it is at full employment, it operates on the PPC.

The production possibilities curve (PPC) is a graph that shows all of the different combinations of output that can be produced given current resources and technology. Sometimes called the production possibilities frontier (PPF), the PPC illustrates scarcity and tradeoffs. In this video, we model tradeoffs and scarcity using the example of a hunter-gatherer who can split their time between two activities. Created by Sal Khan.

Dealing with scarcity is the basis of economics, but what does it mean to say that something is scarce? In this video, we explore the definition of scarcity in economics and how scarce resources are different from free resources.

In a previous lesson we learned that there is the potential for two countries to gain from trade. But it is also possible that there might not be the potential to gain from trade. In this video, we explore the circumstance that would lead to there being no gains from trade.