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Introduction
As stated in the “Hydrostatic Pressure” lab procedure
1
, the objective of the lab is to determine the
magnitude of a hydrostatic force on a plane surface and the location of this force. By associating
height of water, a balance pan, and a counterweight with the Hydrostatic Pressure Apparatus this
will be achieved. Furthermore, these values will be determined by experimentation and
corresponding equations. Determination of hydrostatic forces is applicable to bodies submerged
in a fluid. As stated in
Fundamentals of Fluid Mechanics
2
, These forces develop on the surface
of the body and are a result of the fluid itself. Hydrostatic forces are dependent upon the specific
weight of the fluid, the total area, and depth of the centroid of the body which is reflected in the
equation. Knowledge of the magnitude and location of such forces is crucial to the design of
bodies such as ships, dams and similar hydraulic systems.
The location of the hydrostatic force
is found by determining the coordinates which together are referred to as the center of pressure.
The greater the depth of submergence of the body in the fluid, the closer the center of pressure is
to the resultant hydrostatic force. Hydrostatic pressure is a major factor considered by design
engineers when determining the safety and effectiveness of submerged body applications.
Relevant Theory
When considering a column of fluid with a given depth, the fluid particles at the upper surface of
the column are only subject to atmospheric pressure. The particles below the surface, at a given
depth H, however are subject to an increasing pressure build up. An incompressible fluid is a
fluid with a constant density. In regards to this experiment treating the fluid used as
incompressible is a good assumption being that the only fluid was water originating from the one
source, the faucet. When there is an incompressible column of fluid not subject to shearing
stresses the relationship between pressure and depth is linear. This relationship can be described
by Equation 1.
1
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View Full DocumentP
=γ×
H
+
P
0
(1)
P = Pressure at Depth H
γ = Specific Weight of fluid
P
0
= Pressure at surface
According to Pascal’s law; the pressure at a point in a fluid at rest, or in motion, is independent
of direction as long as there are no shearing stresses present. This means that an object fully
submerged in a fluid is subject to pressure forces from all directions on every face of the object.
Pascal’s law applies to this experiment.
When an object is partially or fully submerged, in a fluid, the hydrostatic pressure acts on all
faces of the object submerged in the fluid.
As previously mentioned, if this fluid is
incompressible and not subjected to shearing stresses, the pressure will vary linearly with depth.
The pressure acting on these surfaces will result in a Resultant Force, F
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 Spring '08
 CAG

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