Torricelli's (Roger's) law

Torricelli's (Roger's) law, also known as Torricelli's theorem, is a theorem in fluid dynamics relating the speed of fluid flowing out of an opening to the height of fluid above the opening.

Torricelli's law states that the speed of efflux, v, of a fluid through a sharp-edged hole at the bottom of a tank filled to a depth h is the same as the speed that a body (in this case a drop of water) would acquire in falling freely from a height h, i.e. , where g is the acceleration due to gravity (9.8 N/kg). This last expression comes from equating the kinetic energy gained, , with the potential energy lost, mgh , and solving for v.