Measurements of continous physical quantities

[N S]

I was wondering how accurate the measurements of in a typical chemistry lab are of continuous physical quantities like temperature, volume, etc. are in practice. For example, when the temperature of a large body is declared, how does one measure it? Does one calculate the average from all the particles in the body, or what? I hope anyone who is experienced in practice would clarify this doubt.

Thank you.

[studiot]

You have asked a very good question, that is worthy of more than a few moments thought.

 

Do you know the difference between intensive properties and extensive properties?

 

Extensive properties are additive. They depend on the quantity of matter so each tiny element of the body contributes and they all add up.

 

Examples are mass and volume.

Both of these can be measured pretty accurately.

 

Intensive properties, however, do not depend upon the quantity of matter.

 

Examples are temperature, density and pressure.

 

Normally we want one single value to represent the whole body concerned. By asking this we are effectively want the whole to be homogenous and isotropic.

Chemists try to can achieve this by stirring for instance.

 

When the body is not homogenous, ie the property varies from point to point within it we can indeed take an average, summed over the whole body (or part of it)

 

An example would be the average surface temperature of the earth.

 

Intensive properties are therefore, by nature likely to be less accurately availabale than extensive ones.

 

Does this help?

Edited September 28, 2013 by studiot

[N S]

Yes, I see it now. I had studied intensive and extensive properties too, and now I see that my question was needless in case of homogenous and isotropic bodies.

 

When chemists, say, stir a solution, they can calculate the heat induced; but at the same time, some heat would be exiting or entering the container; so I get an idea of the assumptions involved.

 

Thanks for clarifying (and confirming) my doubts.