FORMATION AND USAGE OF DIFFERENTIAL MOMENTUM EQUATION¹⁾

The differential momentum equation in fluid mechanics is a fundamental equation, which is usually called the motion equation in textbook. The Navier-Stokes equation can be deduced from the momentum equation by adding some assumptions. The present manuscript shows the formation and usage of the equation. The equation was once reported in the work in 1828 of French Augustin L. Cauchy (1789—1857). George G. Stokes (1819—1903) in England could be the first person who used the equation correctly in the flow problem of constant-viscosity fluid according to the literatures. Moreover, English Ronald S. Rivlin (1915—2005) could use the equation in the viscoelastic flow problem firstly.