# The Pressure Variation with depth in various Water Bodies

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1. Oct 2, 2015

### sandeep singh

1. The problem statement, all variables and given/known data
i want to know about the variation in pressure according to varo=ious depth in different water bodies like for river, lake, stream, and all with the possibility of having fresh water or salty water. (not talking about oceans) may be shore of a sea will also work.
2. Relevant equations
pressure in water is rho * h * g
kindly help if you have any helpful data or solutions. Thanks in advance.

2. Oct 2, 2015

### SteamKing

Staff Emeritus
Well, what exactly do you want to know? The formula ΔP = ρ g h says it all.

There may be some variation in the density of the water in a particular body of water, but it typically ranges from 999 kg/m3 for fresh water to 1025 kg/m3 for sea water. Some extremely salty bodies of water, like the Dead Sea or the Great Salt Lake, have even higher densities.

3. Oct 2, 2015

### sandeep singh

i wanted to know how much pressure a car (specially door) experience when it fell off into the river or lake in an accident. As a person trapped inside is not able to push the door open due to this pressure. and i m even confused how to know it exactly as it varies with running water and steady water also...

4. Oct 2, 2015

### SteamKing

Staff Emeritus
There is a slight change in pressure when water is flowing, but for practical purposes, like trying to open a car door when the car is submerged, this makes little difference.
In such circumstances, it is better to let the interior of the car fill with water to equalize the pressure inside and outside the car. Then, the door may be opened with relative ease, assuming that no structural damage has occurred to the car which might jam the door closed.

5. Oct 2, 2015

### sandeep singh

thanks for your reply.. so do i still use the same equation (delta p) = (rho) * g * h .....for calculation of the exact pressure experienced by the car door for my project...??

6. Oct 3, 2015

### SteamKing

Staff Emeritus
Yes, this formula still works. But pressure is not the only thing you are looking for here.

When pressure acts over a surface, a force is created. It's this force which must be overcome in order to open the door.

7. Oct 3, 2015

### 256bits

For still water that will work fine.
But if equal pressures are on both sides of the door, the actual pressure doesn't matter.

In moving water, the car orientation will be a factor.
If the car is facing upstream or perpendicular to the water flow, the velocity of the water will act to hinder opening up the door.

For a car facing downstream, the flowing water will act to open up the door for you.

I am sure you have experienced the same troubles with opening a door in the air, where the wind can fling open the door and you have to hold on to it so it doesn't fly off, or you yourself using more force to push open the door if the wind is acting against it.

8. Oct 3, 2015