Download Hydrostatic force - Centre of Pressure Lab Report PDF

TitleHydrostatic force - Centre of Pressure Lab Report
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Page 6

yp = h” – ( H – d) = mL/ (ρgBD (d – D/2)) – ( H – d)

Using the equation for the centre of pressure, we can determine the equations
for the theoretical h” and centre of pressure

h = {{{D} ^ {2}} over {12} + {( d- {D} over {2} )} ^ {2}} over {( d- {D} over {2} )} +H-d

and yp = d – D/2 +





Figure 1 shows a general layout of the hydrostatic force apparatus. Water is
contained in a rectangular tank into which a quadrant tank is immersed. The
size of the quadrant tank and the related dimensions of the set-up are shown in
Figure 2. In Figure 2, C is the centroid of the projected area of the vertical face of
the quadrant tank. The centre of pressure of the vertical force acting on the
same vertical face is represented by the point P. The horizontal distance
between the pivot point (marked as a filled triangle) and the balance pan or
weight hanger is referred to as L. the vertical distance between the bottom of
the quadrant face and the pivot arm is known as H. The height and width of the
quadrant face is D and B, respectively. The approximate dimensions of these
variables are shown in the following table.

Length of Balance L 0.275m Distance from weight hanger to pivot

Quadrant to Pivot H 0.200m Base of quadrant face to pivot

Height of

D 0.100m Height of vertical quadrant face

Width of

B 0.075m Width of vertical quadrant face

In the set-up, the line of contact of the knife-edge pivot coincides with the
vertical face of the quadrant tank. Thus, of the hydrostatic forces acting on the
immersed quadrant, only the horizontal thrust acting on the vertical face of the
tank will exert a counter-clockwise moment about the knife-edge axis. In
addition to the quadrant clamping screw the balance arm incorporates a balance
pan, an adjustable counterbalance and an indicator which shows when the arm
is horizontal. This is important as a horizontal arm coincides with the condition

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