Changes

'''Fluid dynamics''' is the study of how [[fluid]]s move. Fluids include [[water]] and [[Gas|gases]] (such as [[air]]).<ref>http://virtualskies.arc.nasa.gov/glossary/F.html</ref> Fluid dynamics is also known as continuum mechanics, as fluids cannot be treated as point objects; [[Classical_mechanics#Newton.27s_Three_Laws|Newton's second law]] thus becomes Euler equation

'''Fluid [[dynamics]]''' is the study of how [[fluid]]s move. Fluids include [[water]] and [[gas]]es (such as [[air]]).<ref>http://virtualskies.arc.nasa.gov/glossary/F.html</ref> Fluid dynamics is also known as continuum mechanics, as fluids cannot be treated as point objects; [[Classical mechanics#Newton.27s Three Laws|Newton's second law]] thus becomes Euler equation

<math>\frac{D\mathbf{u}}{Dt} = - \frac{1}{\rho}\nabla p + \mathbf{g},</math>

<math>\frac{D\mathbf{u}}{Dt} = - \frac{1}{\rho}\nabla p + \mathbf{g},</math>

where <math>\rho</math> is the [[density]] of the fluid, '''u''' its velocity and '''g''' the gravitational acceleration. The [[operator]] <math>D/Dt = \partial/\partial t + (\mathbf{u}\cdot\nabla)</math> is the convective derivative, the rate of change of a certain quantity ''A(t)'' of the fluid as it is carried by the fluid (hence the presence of '''u'''). Euler equation is then a differential operation explicitly relating the effects of the gravity and the gradient of pressure on the velocity of the fluid.

where <math>\rho</math> is the [[density]] of the fluid, '''u''' its velocity and '''g''' the gravitational acceleration. The [[operator]] <math>D/Dt = \partial/\partial t + (\mathbf{u}\cdot\nabla)</math> is the convective derivative, the rate of change of a certain quantity ''A(t)'' of the fluid as it is carried by the fluid (hence the presence of '''u'''). Euler equation is then a differential operation explicitly relating the effects of the gravity and the gradient of pressure on the velocity of the fluid.

As long as the [[speed of sound]] is much larger than '''u''', the density <math>\rho</math> of the fluid can be considered as constant (incompressible).

As long as the [[speed of sound]] is much larger than '''u''', the density <math>\rho</math> of the fluid can assumed to be constant (incompressible) in most situations.

==References==

==References==