Bernoulli's principle states that flowing fluids like air and water press less than still fluids and that pressure decreases quadratically with speed; i.e., with speed-squared.

One quarter of a millennium ago, Daniel Bernoulli pioneered use of kinetic theory that molecules moved and bumped things. He also knew that flowing fluids pressed less, but he did not connect these ideas logically. In Hydrodynamica, Daniel's logic that flow reduced pressure was obscure, and his formula was awkward. Daniel's father Johann, amid controversy, improved his son's insight and presentation in Hydraulica. This research was centered in St. Petersburg where Leonard Euler, a colleague of Daniel and a student of Johann, generalized a rate-of-change dependence of pressure and density on speed of flow. Bernoulli's Principle for liquids was then formulated in modern form for the first time.

In this same group of scientists was D'Alembert, who found paradoxically that...