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Soumalya

- 183

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I am looking for an explanation to the above statement.

If we consider a vertical stream of a liquid flowing through an orifice at the bottom of a liquid filled open tank, we observe the streamlines to be nearly straight at the exit. Applying, Newton's second law of motion across these straight streamlines (radius of curvature is infinite)one can easily show that the pressure at a point on the surface of the jet(often atmospheric pressure) is equal to the pressure at a point within the jet (assuming both points are at the same horizontal plane surface normal to the free jet so that elevation heads are the same for both the points).Thus, for a vertical vertically downward flowing free jet of liquid pressure is uniform throughout and the same as the surrounding or atmospheric pressure.

But again if we consider a horizontal free jet of a liquid, and apply Newton's second law of motion across the straight streamlines at the exit, the difference in pressure between a point on the surface of the jet (atmospheric pressure) and at a point within the jet is not zero as was in the previous case since both points are at different elevations this time. So, application of F=ma normal to the streamlines (straight) implies that pressure should vary hydrostatically within the free jet as is true for straight streamlines (as in open channel flows).

But even for horizontal free jets the pressure at all points within the jet is said to be equal to the pressure surrounding the jet which is atmospheric pressure under normal operations.

Any clarification on the possible misinterpretation of the analogy presented above would be highly appreciated.

Thank You