4.5 Angular Momentum Principle
The angular momentum principle states that the sum of the moments acting on any fluid system is equal to the rate of change of the angular momentum of the system. The angular momentum principle is derived from Newton’s second law of motion by integrating Newton’s second law over a finite-sized system. The angular momentum principle is particularly useful in determining the locations of resultant forces exerted by moving fluids.
Governing equation. Consider a fluid system containing a fixed mass of fluid. If the system is composed of elements of mass δm, then the force acting on each fluid element, δF, can be expressed using Newton’s second law (i.e., the law of conservation of linear momentum) as
where v is ...
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