# Lagrangian and eulerian descriptions of phenomena...

 Sci Advisor P: 5,523 The two viewpoints are equivalent, but some problems are easier to write down in one particular choice of coordinates. For example, if you want to describe the flow of fluid through a channel, IIRC the Lagrangian viewpoint means you pick a control volume dV and watch the fluid flow through it (i.e. stand on the river bank and watch a static point in space), while the Eulerian view means you choose a fluid element dv and watch it deform over time (i.e. follow a material point in time). In continuum mechanics, especially fluid mechanics, the Eulerian description is preferred because it's a more natural way to describe how deformation and flow carry momentum and energy, by using the total derivative D/Dt =$\frac{\partial}{\partial t} + v\bullet \nabla$.