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(a) Conservation of Mass
The conservation of mass equation says that the mass is conserved. It is also known as the continuity
equation. The continuity equation is written as:

(b) Conservation of Momentum
The conservation of momentum is based on Newton's second law that F ¼ ma, where m is the mass of
the fluid particle and a is its acceleration.
When applied to a fluid particle under the action of pressure, viscous and body forces constitute a set
of momentum equations. In the x-direction

In the y-direction

and in the z-direction,

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