How can I calculate underwater pressure quickly

1. Jul 14, 2015

Charlie Kay

Does anyone know a simple formula to calculate underwater pressure?

2. Jul 14, 2015

Staff: Mentor

3. Jul 14, 2015

Charlie Kay

I have the formula "P=r*g*h" when r=fluid density, g=Acceleration of gravity and h=height of fluid.

Got this off NASA

4. Jul 14, 2015

Staff: Mentor

Same thing. ($\rho$ is the common symbol for density.)

5. Jul 14, 2015

Bandersnatch

The simplest way you can get is 1 extra atmospheric pressure per 10 metres of water column.

6. Jul 14, 2015

Charlie Kay

Brilliant, that's just what I was looking for! :-)

7. Jul 14, 2015

Charlie Kay

How much Is normal atmospheric pressure?

8. Jul 14, 2015

Bandersnatch

1 atm or very close to 1 bar, or very close to 100 000 Pascals.

In the spirit of the forum I'd encourage you to take the earlier-posted equations and plug in the numbers for 10 metres of water, and see if it really comes down to 100 000 Pascals. You need density of water in kg/m^3.

9. Jul 14, 2015

Staff: Mentor

Of course Bandersnatch's answer is an approximation - but quite good enough for all practical purposes. It would be a good exercise to calculate exactly what the pressure increase from ten meters of water is using the $\rho{g}h$ formula - google will find the values of the various physical constants you'll need - and see just how good of an approximation it is, whether it is sensitive to small changes in the temperature of the water.

10. Jul 14, 2015

Charlie Kay

Thanks:-)

11. Jul 14, 2015

Charlie Kay

Just wandering if there are any other formulas for it?!

12. Jul 14, 2015

Staff: Mentor

$\rho{g}h$ is pretty much the gold standard here. You can make additional corrections if $\rho$ or $g$ aren't constant, but for any problem involving reasonable liquids on or around the surface of the earth, these are just rounding errors.

13. Oct 2, 2015

Charlie Kay

Hey guys I've collected some information and I can now calculate "P=r*g*h" It is:

999.99 X 9.81 X 11000 = 107 908 920.9
Fluid Density X Acceleration Due To Gravity X Height Of Fluid = Pressure

But this is it pascal, does anyone know the conversion rate from pascal to bar???

14. Oct 2, 2015

Staff: Mentor

1 bar = 100,000 Pa.

15. Oct 2, 2015

Staff: Mentor

While we appreciate the traffic, Google will answer these questions in milliseconds...

16. Oct 2, 2015

DaveC426913

And don't forget what 'snatch said: "1 extra atmospheric pressure per 10 metres".
People often forget there's an initial 1 atm at sea level.

17. Oct 2, 2015

Staff: Mentor

That often falls out of the analysis (for example, for a submarine), but yes, that thought should at least be processed at the start of the analysis.

18. Oct 2, 2015

Charlie Kay

But it's not as friendly and it doest'n give you a straight answer

19. Oct 2, 2015

Staff: Mentor

It certainly has its limitations, but it is a life-skill everyone should have.

20. Oct 2, 2015