MaterialDerivative
Fromfluid mechanics, the material derivative is teh Lagrangian method of evaluating a rate of change. Hence the material derivative is a Lagrangian derivative. In the Lagrangian method, the control mass (water in the present case) is not allowed to pass through the control mass boundary; however, its properties, such as heat and momentum, can pass through. In this method of description, the control mass is followed everywhere it goes around in the surroundings, and the fate of any given property transpiring inside it is tracked.