Hydrostatic force test

1. Hydrostatic
Force

2. Procedures
1) Set the water vessel to an angle of
using the detent as shown
2) Counterbalance the unit with rotating slider (the stop pin must be precisely in
the middle of the hole for this)
3) Mount the rider, set the lever arm on the scale (e.g. 1 =150mm)
4) Top up the water until the unit is balanced (stop pin at centre of hole)

3. 5) Read of water level, s and enter it in the prepare worksheet
6) Increase the appended weights in increment of 0.5-1 N and repeat the
measurement

4. Data and analysis
Appended Lever
weight
arm
FG(N)
L(m)
Water
level
S(m)
Calculated
level arm
Id(m)
Resultant
force
Fp(N)
0.16
0.17
0.18
0.19
0.23
0.24
0.25
0.26
0.054
0.056
0.060
0.062
0.092
0.093
0.097
0.098
0.182
0.181
0.180
0.179
0.169
0.169
0.168
0.167
1.073
1.154
1.324
1.414
3.114
3.182
3.461
3.533
3.432
4.432
Appended
weight
moment
(Nm)
0.549
0.583
0.618
0.652
1.019
1.064
1.108
1.152
Water
moment
(NM)
0.195
0.209
0.238
0.253
0.526
0.538
0.581
0.590
Balance
of
moment
(Nm)
0.354
0.374
0.380
0.399
0.493
0.526
0.527
0.562

5. Discussion
1) how to determine the center of pressure?
-To determine the center of pressure, add up all contributions to the force over each small
piece of the area, but multiplied by y .The center of pressure is essentially a weighted average
2) ho the mean x-position of the force can be determined?
-The mean x-position of the force can be determined by similar technique. This is just the
product of inertia for the coordinate system

6. Conclusion
The obtained results showed large discrepancies between the theoretical and experimental values
of the center of pressure, where the experimental ones were larger than the theoretical ones.
These discrepancies might be a result of errors occurred in the experimental procedures or
apparatus; following are some of the possible errors that might have caused the large
discrepancies:
1. Neglecting the weights of the balance.
2. Error in reading, due to errors in taking the reading from the apparatus or from parallax errors
in determining the touching point between the water surface and the pin of the measuring device.
Another result that I noted was related to the fact that with increasing the depth of immersion, the
center of pressure should get closer to the centroid, this fact was correct in the total immersion
region but in the partial immersion the results showed random variation.