1.0 INTRODUCTION
The Hydrostatic Pressure (Model: FM 35) apparatus has been designed to study on the
hydrostatic of an object immersed in fluid. It will enable students to measure the static thrust
exerted by a fluid on a submerged surface while allowing them to compare the magnitude and
direction of the force with theory.
The calculation of the magnitude, direction and line of the hydrostatic forces exerted by a
fluid on a submerged plane surface is important in the design of structures such as drams, meads,
gates, tanks, submarines etc. The pressure which the force acting over a unit face area and varies
linearly with depth. This fact enables us to describe the pressure distribution over a submerged
surface. When the pressure is uniform over a surface, such static pressure on a horizontal surface,
the resultant force is equal to area times the pressure and acts through the centroid of the area.
However, in many cases, such as ids acting on a non-horizontal surface, the situation is more
complex. A general approach has been developed to estimate resultant force and its line of
action.
In this experiment, the reliability of this approach is examined by comparing analytical
values for forces and moments acting on a plane surface with experimental measurements of
these values on the same surface on a partially submerged and fully submerged plane •ace, but
for more clearly to get the result of the concept.
2.0 OBJECTIVES
1. To determine center of pressure on a partially submerged plane surface
2. Compare the Experiment measured values with the theoretically calculated values for
center of pressure
3.0 APPARATUS
1. Weights
2. Ruler
3. Stop Watch
Description and Assembly
Figure 1: Assembly Diagram of Hydrostatic Pressure (Model: FM35)
1. Quadrant
Material
Total Depth of Quadrant, H
Height of Fulcrum above Quadrant, a
Height of End Surface, D
Width, B
Length of Balance, L
: PVC
: 208 mm
: 110 mm
: 98 mm
: 68 mm
: 290 mm
2. Reservoir Tank
Material
Volume
: Clear Acrylic
: 6.67 L
3. Balance Arm
Distance between Suspended Mass and Fulcrum, L
Set of Weights
: 290 mm
: 50 g each
4. Overall Dimension
Length
Width
Height
: 410 mm
: 150 mm
: 280 mm
4.1 PROCEDURE
1. The quadrant is placed on the two dowel pins and fastened to the balance arm using the
clamping screw.
2. L, a, depth d and width b of the quadrant end face are measured.
3. With the Perspex tank on the bench, the balance arm is positioned on the knife edges (pivot).
The balance pan is hanged on from the end of the balance arm. A length of hose is
connected from the drain cock to the sump and a length from the bench feed to the
triangular aperture on the top of the Perspex tank.
4. The tank is leveled using the adjustable feet and spirit level. The counter balance weight is
moved until the balance arm is horizontal.
5. The drain cock is closed and water is admitted until the level reached the bottom edge of the
quadrant.
6. A weight is placed on the balance pan and water is added slowly into the tank until the
balance arm is horizontal.
7. The water level on the quadrant and the weight on the balance pan are recorded.
8. Fine adjustment of the water level can be achieved by overfilling and slowly draining using
the stop cock.
9. The above step is repeated for each increment of weight until the water level reached the
tops of the quadrant end face.
10. Then each increment of weight is removed to note the weight and the water level until the
weight have been removed.
4.0 RESULTS
FILLING TANK
DRAINING TANK
AVERAGE
Height of
Weight,
Water, y1
m1 (g)
Weight,
Height of
m (g)
y (cm)
y (cm )
50
(cm)
2.0
50
1.90
3.55
5.00
6.25
7.50
3.61
12.60
25.00
39.06
56.25
50
100
3.5
100
3.6
100
150
5.0
150
5.0
150
200
6.2
200
6.3
200
250
7.5
250
7.5
250
mavg =
m1 +m2
2
=
50+ 50
2
= 50 g
y1 + y2
2
yavg =
1.8+ 2.0
2
=
= 1.9 cm
y2 = 1.9x1.9
= 3.61
m
y2
=
50 g
3.61 cm2
= 13.85 g/cm2
5.0 DISCUSSION
2
Water, y2
m2 (g)
(cm)
1.8
Calculations:
2
m/y2
(g/cm2)
13.85
7.94
6.00
5.12
4.44
The result obtained from the experiment contains error by comparing it to theory. There is
a large variation between actual and theoretical data. The error occurred are due to several
factors. The factors are:1. The spirit level of the apparatus

Accuracy of spirit level is important because it provides correct level of the apparatus
and reading taken for height of water will more precise.
2. Reading of measurement

Parallaxes reading occur when reading of measurement taken by different people, so
reading taken by one person is suggested in order to obtain more accurate result.
Majority of inaccuracy reading of measurement effected by the incorrect spirit level
of the apparatus.
3. Water used for the experiment

The water used may contain impurities and this will result error occur to reading due
to unclean water giving different density. In order to obtain accurate result pure water
such as distillation water is suggested to maintain density of water ρ = 1000 kg.m3.
Precaution Step:
1. Pouring water into tank

Care must be taken to avoid the quadrant from contact with water when pouring, this
is to prevent any inaccuracy of value taken caused by increases of weight on quadrant
which can affected both reading error on spirit level of apparatus and reading of
measurement.
2. Wind loads

It is recommended to do this experiment in enclosed space, minor error caused by the
wind loads from environment may influence the reading of measurement by
increasing the weight on the quadrant.
6.0 CONCLUSION
From this experiment, it can be conclude that the water filled in should be equivalent to the
water drained out, and then the result will be more accurate.
7.0 APPENDIX