- #1
Philip Wood
Gold Member
- 1,220
- 78
Suppose we have the set up shown in the thumbnail, in which an incompressible fluid moves from left to right, trapped by converging streamlines.
The rate of acquisition, F, of momentum by the fluid is surely
[tex]F = \rho A_2 v_2^2 - \rho A_1 v_1^2
= \rho A_1 v_1^2 \left\{\frac{A_1}{A_2} - 1\right\}[/tex]
in which I've eliminated v2 using the continuity equation, [itex]A_1v_1 = A_2v_2[/itex].
My question is whether there's any simple physical argument which connects this with the Bernoulli relationship for the same sample of fluid, namely:
[tex]p_1 -p_2 = \frac{1}{2} \rho v_2^2 - \frac{1}{2} \rho v_1^2 [/tex]
that is, again using the continuity equation,
[tex]p_1 -p_2 = \frac{\rho}{2} v_1^2 \left\{\frac{A_1^2}{A_2^2} - 1\right\} [/tex]
The rate of acquisition, F, of momentum by the fluid is surely
[tex]F = \rho A_2 v_2^2 - \rho A_1 v_1^2
= \rho A_1 v_1^2 \left\{\frac{A_1}{A_2} - 1\right\}[/tex]
in which I've eliminated v2 using the continuity equation, [itex]A_1v_1 = A_2v_2[/itex].
My question is whether there's any simple physical argument which connects this with the Bernoulli relationship for the same sample of fluid, namely:
[tex]p_1 -p_2 = \frac{1}{2} \rho v_2^2 - \frac{1}{2} \rho v_1^2 [/tex]
that is, again using the continuity equation,
[tex]p_1 -p_2 = \frac{\rho}{2} v_1^2 \left\{\frac{A_1^2}{A_2^2} - 1\right\} [/tex]