Impulse-Momentum Principle For Fluids Formula

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Impulse-Momentum Principle For Fluids Formula

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The Impulse-Momentum Principle is derived from Newton's 2nd law in vector form which states that the rate of change of linear momentum of a body is directly proportional to the external force applied on the body, and this change takes place always in the direction of the force applied.

The resultant force in a given direction acting on the fluid equals the rate of change of momentum of the fluid.

Eq. 1
∑ F = ∑ Q₂ ρ₂ v₂ - ∑ Q₁ ρ₁ v₁

Where:

∑ F = the resultant of all external forces acting on the control volume
∑ Q₂ ρ₂ v₂ = the rate of momentum of the fluid flow entering the control volume in the same direction as the force
∑ Q₁ ρ₁ v₁ = the rate of momentum of the fluid flow leaving the control volume in the same direction as the force

Source:

Vennard, John K. and Robert L. Street, Elementary Fluid Mechanics, John Wiley & Sons, Inc., 1982.