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Hydrostatic pressure
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      Bottle of plastic.

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     1. Cut the top of the plastic bottle.

     2. Make three holes in the bottle with the needle. (the holes shouldn't be on a same direction. This, because when the first hole water jet intensity decreases, it can influence the others water jets)

     3. Add currant to the water. (currant addition to the water is made to turn easier the visualization of the effect)

     4. Fill the bottle with currant water.

     5. Observe the intensity variation of the water jets with height. What happens?

The intensity of the water jet varies with depth. This experience reminds the problems of the divers. A diver that goes until an appreciable depth, when it comes to the surface, he has to go to a depressurizing camera. He could die if he doesn't do it because the human body doesn't tolerate such high pressure variations.

When we dive under water, the pressure increases with depth because the weight of water above our body increases. The hydrostatic pressure is given by the following equation:

where P0 is the atmospheric pressure, r the density of the water, g the gravity, h the depth and P the pressure at that depth.

The hydrostatic pressure variation with depth is shown in the present experiment. The lowest holes give a stronger water jet than the top ones. As the liquid level is lowering, the intensity of all the jets is also decreasing.

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