Experiments on negative gauge pressures and pressures in relative reference systems

The video is one of the educational activities of the Environmental Hydraulics course in the Civil and Environmental Engineering degree program at the Polytechnic University of Bari.
The video presents some hydraulic experiments on pressure. In particular, it demonstrates how creating a vacuum at the top of a tank reduces the internal pressure compared to the external pressure, preventing the liquid from flowing out.
In the second experiment, it is shown that a tank dropped in a vacuum exhibits a constant pressure distribution along the vertical direction, with a pressure value everywhere equal to atmospheric pressure. This balance between internal and external pressure, both equal to atmospheric pressure, prevents the liquid from escaping from the freely falling tank.
For more details, see Chapter 2 (specifically, Section 2.13 on relative equilibrium) of the book: Mossa M. and Patrillo A.F., Idraulica, CEA, Milan, 2nd edition, 2024.
Contribution by Adriano Saracino.