MOMENTUM EQUATION

MOMENTUM

Momentum is the application of Newton's Laws to fluid flow.

Newton's Second law states:

The force on a body equals its rate of change of momentum. Momentum is a vector quantity and is defined as mass x velocity.

The rate of change of momentum is therefore given by:  (d/dt )(mv)

There are typically two possibilities in the use of this equation:-

·         The mass of a body remains constant and its velocity changes

·         The velocities of a body of mass remain constant and the rate of mass changes.

                         Resultant force = rate of change momentum

                                                 = final momentum-initial momentum

                                                 = mv₂ – mv₁

                                  mv₁ and mv₂ are the vector quantities

                         vector difference required to determine the force.

 

·         This is the force applied to the fluid to make it change to direction and speed.

·         There is an equal and opposite force on the duct through which the fluids flows.  (Newton’s third law).

·         This represents the essential principal of fluid machinery turbines or pumps