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Definition:

Hydrostatic pressure is what is exerted by a liquid when it at rest. The height of a liquid column of uniform density is directly proportional to the hydrostatic pressure. The hydrostatic properties of a liquid are not constant and the main factors influencing it are the density of the liquid and the local gravity. Both of these quantities need to be known in order to determine the hydrostatic pressure of a particular liquid.



The formula for calculating the hydrostatic pressure of a column of liquid in SI units is:


Hydrostatic Pressure (Pa or N/m2) = Height (m) x Density (kg/m3) x Gravity (m/s2)


The density of a liquid will vary with changes in temperature so this is often quoted alongside hydrostatic pressure units while the local gravity depends on latitudinal position and height above sea level.
For convenience the most common standard for hydrostatic pressure is metres of water or feet of water at 4 deg C (39.2 degF) with a standard gravity of 9.80665 m/s2.
The density of pure water at 4 deg C is very close to 1000 kg/m3 and therefore this has been adopted as the standard density of water. Another reason for the significance of choosing 4 deg C is that it is very close to the temperature that water reaches its maximum density. In practical terms hydrostatic pressure units are rarely absolutely precise because the temperature of any liquid is not always going to be 4 deg C. You will also come across another temperature standard of 60 deg F (15.56 deg C). This can lead to confusion and inaccuracies when the temperature is not labelled alongside the hydrostatic pressure unit. For most applications these differences are not significant enough to influence the results since the reading accuracy is often much wider than the difference in the pressure unit conversion factor at these 2 temperatures. In summary hydrostatic pressure units are a very convenient method for relating pressure to a height of fluid but they are not absolute pressure units and it is not always clear what density/temperature has been assumed in their derivation, so be very cautious when using them for high precision level measurements. In fact some institutions are discouraging their use because of the very reasons mentioned above.




Hydrostatic Pressure Experiments:
Basement Water:
http://www.youtube.com/watch?v=5b2B3Y5ydFI&feature=related


Application of hydrostatic pressure in siphoning:


http://www.youtube.com/watch?feature=player_embedded&v=RSxuh2lpAXw





SIMPLE DEMONSTRATION BY US!


Our group aims to present the effect of hydrostatic pressure by comparing the jets of fluid streaming out of different holes made in a vessel filled with water.


Materials and Apparatus:

- A skewer
-A pair of gloves
- Tape
- Food dye
- A 1.5L bottle
-Water

Procedure:


1) Using the skewer, puncture a few holes along the height of the bottle. Make sure that the holes are uniform in size.


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2) Using the tape, seal up all the holes that you have punctured.

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3) Let it stand upright and fill it with water. It should look something like this.

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4) Add a few drops of food dye so that the stream of water leaving the bottle would be made more visible.

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So here's the video:

http://www.youtube.com/watch?v=GkJzVhQHv_k&feature=youtu.be



Explanation:
First of all, let us assume that the density of the liquid remains constant. As gravity acting downwards on the liquid is also said to be constant at 9.8m/s^2 , the independent variable would be the height of the liquid in the column. Hence, the dependent variable would be the hydrostatic pressure of the column of liquid.
As the bottom hole has more height as compared to the one at the top, there is so much more water above it causing a larger force pushing down and thus, resulting in the jet of water to stream out of the hole with a larger force too. This is evident from the larger distance that the stream of water from the bottom hole makes, since it has higher energy as compared to the hole at the top.
Besides, we can also compare the speed at which the stream of water leaves each hole. Maybe we can bring a mini turbine towards the stream of water and observe the speed at which it rotates. Likewise, we can use a high speed camera and track the speed at which the stream of water is leaving the bottle at different holes, before doing any comparison.



Risk Assessment :l





Done by:
Joshua Tan Xian Da
Elton Pan Zi Heng