Neurons (or nerve cells) are specialized cells that transmit and receive electrical signals in the body. Neurons are composed of three main parts: dendrites, a cell body, and an axon. Signals are received through the dendrites, travel to the cell body, and continue down the axon until they reach the synapse (the communication point between two neurons).

Ancient Egypt was an early example of a massive civilization spanning thousands of years. Sal explains this history in an overview.

Why is Mesopotamia considered the "cradle of civilization"? Sal explains the history of the early empires on the Tigris and Euphrates rivers.

High level overview from Ancient Egypt to Babylon with reference to stories from the Old Testament.

This overview of Ancient Persia explains the origins of the term "Persia" and Zoroastrianism; it also puts the Median, Achaemenid, Seleucid, Parthian, Sassanian dynasties in context.

Introducing angular momentum conceptually starting from linear momentum. Also covers some real-life examples. Created by Sal Khan.

David explains the meaning of angular displacement, angular velocity, and angular acceleration. Created by David SantoPietro.

In uniform circular motion, angular velocity (𝒘) is a vector quantity and is equal to the angular displacement (Δ𝚹, a vector quantity) divided by the change in time (Δ𝐭). Speed is equal to the arc length traveled (S) divided by the change in time (Δ𝐭), which is also equal to |𝒘|R. And arc length (S) is equal to the absolute value of the angular displacement (|Δ𝚹|) times the radius (R).

Learn how to use jQuery to animate elements in custom ways, like animating their sizes, borders, and spacing, to whatever values you specify.

Learn how to use jQuery to show, hide, and toggle elements with animation effects.

The annual percentage rate (APR) that you are charged on a loan may not be the amount of interest you actually pay. The amount of interest you effectively pay is greater the more frequently the interest is compounded. In this video, we calculate the effective APR based on compounding the APR daily. Created by Sal Khan.

Interpreting an excerpt of Brutus No. 1, the most well-known of what will be eventually called the "Anti-Federalist Papers," which argued against the ratification of the Constitution of 1787.

DNA is composed of two strands of nucleotides held together by hydrogen bonding. The strands each run from 5' to 3' and run in antiparallel, or opposite, directions from one another.