51/ algebra angular momentum conservation

Macroscopic and Microscopic Balances Three postulates, regarded as laws of physics, are fundamental in fluid mechanics. These are conservation of mass, conservation of momentum, and con-servation of energy. In addition, two other postulates, conservation of moment of momentum (angular momentum) and the entropy inequality (second law of thermodynamics) have occasional use. The conservation principles may be applied either to material systems or to control volumes in space. Most often, control volumes are used. The control volumes may be either of finite or differential size, resulting in either algebraic or differential consei vation equations, respectively. These are often called macroscopic and microscopic balance equations. 

This number can be reduced to 12 by transforming the coordinates [20] so that terms in the momentum components of the center of mass are separated. As they must remain constant, these terms can be ignored. If account were also taken of the constancy of total angular momentum, the number of equations could be decreased still further, but the algebra required is formidable and conservation of angular momentum throughout the calculated trajectory can be used to check the accuracy of the computation. 

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