Torricelli's law, also known as Torricelli's theorem, is a theorem in fluid dynamics relating the speed of fluid flowing from an orifice to the height of fluid above the opening. The law states that the speed v of efflux of a fluid through a sharp-edged hole at the bottom of the tank filled to a depth h is the same as the speed that a body would acquire in falling freely from a height h , i.e. v = 2 g h , where g is the acceleration due to gravity. This expression comes from equating the kinetic energy gained, 1 2 m v 2 , with the potential energy lost, m g h , and solving for v . The law was discovered (though not in this form) by the Italian scientist Evangelista Torricelli, in 1643. It was later shown to be a particular case of Bernoulli's principle.