The study of the properties of liquids in motion and based on the principles of hydrodynamics and hydrostatics. The principles have been known for millennia with recorded evidence of irrigation canals and dams having been used in Egypt and Mesopotamia (now modern-day Iraq). Italian physicist Evangelista Torricelli (1609–47) noted in 1644 that the velocity of a flowing liquid is proportional to the square root of the water head. Swiss scientist Daniel Bernoulli (1700–82) obtained the relation between wall pressure, velocity, and elevation in 1738, using the word ‘hydrodynamica’ to describe the synthesis between conceptions of hydrostatics and hydraulics. Many other scientists have subsequently developed the subject area using Newtonian dynamics and differential calculus to describe the flow in pipes and channels, leading to many key concepts and the establishment of theorems including vortex motion, fluid resistance, airfoils, meteorological fronts, and statistical approaches to turbulence.