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Pressure and Manometers
What will be the (a) the gauge pressure and
(b) the absolute pressure of water at depth 12m below the surface? rwater
= 1000 kg/m3, and p atmosphere = 101kN/m2.
|Volume moved from left to right
The head being measured is 3% of 3mm = 0.003x0.03 = 0.00009m
This 3% represents the smallest measurement possible on the manometer, 0.5mm = 0.0005m, giving
The magnitude of the resultant force on a submerged plane is:
R = pressure at centroid area of surface
This acts at right angle to the surface through the centre of pressure.
By the parallel axis theorem (which will be given in an exam), , where IGG is the 2nd moment of area about a line through the centroid and can be found in tables.
For a rectangle
As the wall is vertical, ,
For a triangle
Depth to centre of gravity is .
Distance from P is
Distance from P to centre of pressure is