Sign Convention For Work
The motivation for the specific sign conventions of thermodynamics comes from early development of heat engines. When designing a heat engine, the goal is to have the system produce and deliver work output. The source of energy in a heat engine, is a heat input.
If the volume compresses (delta V = final volume - initial volume < 0), then W < 0. That is, during isobaric compression the gas does negative work, or the environment does positive work. Restated, the environment does positive work on the gas.
If the volume expands (delta V = final volume - initial volume > 0), then W > 0. That is, during isobaric expansion the gas does positive work, or equivalently, the environment does negative work. Restated, the gas does positive work on the environment.
If heat is added to the system, then Q > 0. That is, during isobaric expansion/heating, positive heat is added to the gas, or equivalently, the environment receives negative heat. Restated, the gas receives positive heat from the environment.
If the system rejects heat, then Q < 0. That is, during isobaric compression/cooling, negative heat is added to the gas, or equivalently, the environment receives positive heat. Restated, the environment receives positive heat from the gas.
Read more about this topic: Isobaric Process
Famous quotes containing the words sign, convention and/or work:
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Yet, for necessity of present life,
I must show out a flag and sign of love,
Which is indeed but sign.”
—William Shakespeare (1564–1616)
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—Martha Nussbaum (b. 1947)
“As for my own business, even that kind of surveying which I could do with most satisfaction my employers do not want. They would prefer that I should do my work coarsely and not too well, ay, not well enough. When I observe that there are different ways of surveying, my employer commonly asks which will give him the most land, not which is most correct.”
—Henry David Thoreau (1817–1862)