Walk through the logic of determining what kind of good has the most elastic demand in this video.

There are several factors that affect how elastic (or inelastic) the price elasticity of demand is, such as the availability of substitutes, the timeframe, the share of income, whether a good is a luxury vs. a necessity, and how narrowly the market is defined. We explore each of these in this video.

The Paleolithic and Neolithic eras of the Stone Age. Created by Sal Khan.

The Paleolithic and Neolithic eras of the Stone Age. Created by Sal Khan.

Alexander's Empire fragments into Seleucid Persia, Ptolemaic Egypt and Antigonid Macedonia (and other kingdoms) and gives rise to the Hellenistic Period.

An introduction to the difference between wealth and income. Created by Sal Khan.

Learn about how particles move from an area of greater concentration to an area of lesser concentration through the process of diffusion.

Learn about diffusion, osmosis, and concentration gradients and why these are important to cells. Created by Sal Khan.

Using Title IX as an example of how the federal bureaucracy has rule making and discretionary authority as it implements laws.

An overview of what happens when the conditions for Hardy-Weinberg equilibrium are not fulfilled. Created by Sal Khan.

Using a one-dimensional number line to visualize and calculate distance and displacement. Created by Sal Khan.

An introduction to the difference between distance traveled and displacement. Created by Sal Khan.

Relating angular displacement to distance traveled (or arc length) for a ball traveling in a circle. Derivation of formula for arc length.

John Dickerson discusses how the sitting president's party typically performs in midterm election years. John Dickerson is co-host of CBS This Morning. He was previously CBS News' Chief Washington Correspondent, Political Director and anchor of Face The Nation. Dickerson is also a contributor to Slate's Political Gabfest and to The Atlantic. During the 2016 presidential campaign, Dickerson moderated CBS News' two presidential debates. Prior to CBS, Dickerson was Slate Magazine's Chief Political correspondent and covered politics for twelve years for Time magazine.

Learn about the Doppler effect and how it explains the change in frequency of a wave when its source and an observer are moving. Created by Sal Khan.

Understanding the differences between the dot and cross products. Created by Sal Khan.