Atmospheric pressure 1Atm or 100 kPa?

[flatmaster]

Ignoring normal variations, I've always been told that atmospheric pressure is...

1 Atm = 101,325 Pa

However, Wikipedia says atmospheric pressure was re-defined in 1999 to be exactly 100 kPa. This would mean that atmospheric pressure is now 0.98692 Atm.

http://en.wikipedia.org/wiki/Atmospheric_pressure

I'm writing a lab activity for high school students. From what I've read, it seems that both conventions are used. Which convention should be used?

 

[mgb_phys]

it depends who you work for !
IUPAC use 100Kpa but NIST use 101.3Kpa, as do most ISO standards.

None of these change the fact that the average air pressure is 101.3kpa

 

[flatmaster]

ok. average atmospheric pressure = 1 Atm and that's that. Good enough for now. I'll let them be confused later.

 

[Borek]

That is part of "what is STP" question:

http://en.wikipedia.org/wiki/Standard_conditions_for_temperature_and_pressure

Choose your units first - if you decide to use atm, go for 1 atm, if you decide for SI - go for 100 kPa. I would stick to SI, but that's my humble opinion, skewed by metricity of the country I live in.

 

[flatmaster]

Using Atm allows me to compare 1Atm to 4.5 Atm at the bottom of a local lake and 3,000,000 Atm at the core.

 

[Borek]

Could be a good point, but... where do you get 4.5 atm from?

 

[flatmaster]

Could be a good point, but... where do you get 4.5 atm from?

It's a local lake. I calculated it myself from the depth.

 

[Borek]

So I guess lake is 45 m deep?