David explains what beat frequency means, how to find it, and solves a sample problem involving beat frequency. Created by David SantoPietro.

An overview of the run up to and very beginnings of World War II.

An overview of the run up to and very beginnings of World War II.

Early Muslims escape Quraysh persecution by migrating to Medina in 622. With Medina as the base of their community, they are able to convert Mecca and most of Arabia to Islam during the remainder of the life of Muhammed (next 10 years).

The early life of Muhammad including his work as a merchant, his marriage to Khadijah, his early revelations and the persecution of early Muslims by his own Quraysh tribe.

This art history video discussion examines Giovanni Bellini's "Saint Francis in the Desert", c. 1480, oil and tempera on poplar, 124.5 x 141.9 cm (The Frick Collection, New York).

This art history video discussion looks at Giovanni Bellini and Titian, The Feast of the Gods, 1514 and 1529, oil on canvas (National Gallery of Art).

In this video Karl talks to Ben Eater about his improvements to the Spider bot platform. Created by Karl Wendt.

This art history video discussion looks at Bonaventura Berlinghieri's "Altarpiece of St. Francis", c. 1235 (Church of San Francesco, Pescia, Italy).

This art history video discussion looks at Bernini's "Apollo and Daphne", 1622-25 (Galleria Borghese, Rome).

This art history video discussion examines Gian Lorenzo Bernini's "Bust of Medusa," marble, c. 1644-48 (Capitoline Museum).

This art history video discussion looks at Gian Lorenzo Bernini, Cathedra Petri (or Chair of St. Peter), gilded bronze, gold, wood, stained glass, 1647-53 (apse of Saint Peter's Basilica, Vatican City, Rome). According to tradition, St. Peter himself, the founder of the institution of the Church and considered the first pope, sat on the ancient wooden chair that is encased within this larger bronze and gold chair.

This art history video discussion looks at Gian Lorenzo Bernini, David, 1623-24, marble (Galleria Borghese, Rome).

This art history video discussion looks at Gian Lorenzo Bernini's "Ecstasy of Saint Theresa", 1647-52 (Cornaro Chapel, Santa Maria della Vittoria, Rome).

This art history video discussion examines Gian Lorenzo Bernini's "Pluto and Proserpina" (also know as the Rape of Proserpina), 1621-22, marble (Galleria Borghese, Rome). Proserpina is the Latin varient of the mythic Greek Persephone.

This art history video discussion looks at Gian Lorenzo Bernini's "Saint Peter's Square (Piazza San Pietro)", Vatican City, Rome, 1656-67.

This art history video discussion looks at Gian Lorenzo Bernini's "Sant'Andrea al Quirinale", 1658-70, Rome; commissioned by Cardinal Camillo Francesco Maria Pamphili for the nearby Jesuit seminary.

This is the first of two videos where Sal derives Bernoulli's equation. Created by Sal Khan.