MN/m2

Hydrostatic pressure is the pressure caused by a static column of liquid (water say).

The variables you quote MN/m^2 stands for Mega Newtons per square metre..

Which is a unit of pressure measurement..

John.

Actually the correct SI units are pascals and

1 pascal = 1 newton meter ^-2 = 0.0040149 inches of water

Pascals however are generally not used by themselves an for atmospheric pressures HPa Hecta pascals which are 100 pascals are used for other pressures Kilo pascals (KPa = 1,000 pascals) and Mega pascals (MPa = 1,000,000) are used.

MN/m2 stands for Mega Newton per square meter.i.e. 1000000 Newton per square meter

MN/m² dose stand for 1 million Newtons per square meter but it is not a SI unit. The SI unit for pressure is the pascal and

1 MN/m₂ = 1Mpa = 4,014.9 in H₂0 ≈ 335 feet of water

It's important to try and stick with SI units so we are all talking about the same thing. Just ask NASA when people don't all use the same units.

Masu, I agree, but unfortunatly I can think of at least a dozen different units used by people when talking about pressure...

I've been in to companies and they talk about Newtons per square metre...

Yes it is spelt 'metre', its only the Americans who spell it 'meter'!

psi, inches water gauge, millimetres mercury, torr, pascals, bar, millibar, kg per square cm etc... etc...

Even tonnes per square metre.....!!

I've yet to come across a general unit of pressure measurement that everyone uses, personally I like to think of pounds per square inch, but that's my preference...

When going to meet a customer to talk about pressure measurements I ALWAYS take along a conversion slide rule with me... So when they start talking of unfamiliar units I can quickly check to see whether its a lot or not much !!!!

John.

Hi Electroman. I know what you mean, there seem to be more ways to measure than pressures that need reading. Medicine uses mm Hg, gas fitters use in H₂O, control people use PSI etc. However the official Standard International unit is the pascal. In Australia all pressure measurements should be expressed in pascals or one of its multiples. Even the barometric pressure is expressed in Hpa.

The thing that annoys me is when people that don't understand the metric system and use things like Kg/cm². This is really meaningless because Kg is a measure of mass not force. It comes from the old imperial system where there was no units for force so they just used the weight. Whenever I see something like that written down it tends to convey that the person that wrote it doesn't know what they are talking about. Hopefully some day we will all use the SI units, it certainly removes a lot of confusion and makes engineering calculations one hell of a lot simpler. Maybe we could even avoid some disasters like Mars explorers crashing or rockets blowing up.

Personally whenever I need to do a calculation a always convert everything to metric and if need be convert back at the end.

Yes Masu I agree, it would save so much confusion!!

I'm quite happy using millibars and bar and remembering that a pascal is a tenth of a millibar (I think!)...

By the way don't forget that originally it wasn't pounds per square inch the initials psi stood for poundals per square inch...

Of course a poundal is a unit of force ( 1 lb with gravity of 32 feet per second??). Even that is a little to old for me!!

I think it can be much easier picturing and calculating pressures with units that are readily available...

My time spent working with old air gauging systems which use as a pressure source a piston in a tapered cylinder means that its easy to know accurately the cross sectional area of the piston in cm^2 or inches^2 and just adding weights to the piston gives the air pressure you need...

Not strictly true but it worked... Even today there are some old dead weight pressure calibrators with the cross sectional area of the piston marked and just add weights to get the pressure you want!!

John.

Oooops!! I think I'm going to get some 'stick' for commenting about the American's spelling of metre....

"Yes it is spelt 'metre', its only the Americans who spell it 'meter'!"

Maybe not until they wake up on Monday afternoon though....

John :-)

thanks for the help guys

Reply to #4 and #5 - pascal and newton per m² are the same.