Torricellis law, also known as Torricellis 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  of efflux of a fluid through a sharp-edged hole at the bottom of the tank filled to a depth  is the same as the speed that a body would acquire in falling freely from a height , i.e. , where  is the acceleration due to gravity. This expression comes from equating the kinetic energy gained, , with the potential energy lost, , and solving for . 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.