**Conservation of Energy (Bernoulli’s Theorem)**

Total Pressure = Dynamic Pressure (½ρV^{2}) + Static Pressure = Constant

The total energy of an airstream comes in two forms: potential energy (static pressure) and kinetic energy (dynamic pressure).

The total pressure of the airstream is the sum of the static pressure and the dynamic pressure and must remain constant, according to __the law of conservation of energy.__

Thus, an increase in one form of pressure, must result in a decrease in the other.

Dynamic pressure (q) is expressed by:

*q= 1/2* ρ* V*^{2}

Assuming the total pressure to be constant, the static pressure and the dynamic pressure vary inversely: If one increases the other decreases and vice-versa.

*In Conclusion:*

- In a
__convergent duct__, flow speed increases,**increasing dynamic pressure (= velocity)**. If dynamic pressure increases,**static pressure and static temperature decrease.**

- In a
__divergent duct__, flow speed decreases,**decreasing dynamic pressure (=velocity)**. If dynamic pressure decreases,**static pressure and static temperature increase.**

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