Regarding the definition of Work

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Homework Help Overview

The discussion revolves around the definition of work in the context of thermodynamics, particularly regarding the sign convention used when a gas expands or contracts. Participants are exploring the differences between AP Physics and various textbooks on this topic.

Discussion Character

  • Conceptual clarification, Assumption checking

Approaches and Questions Raised

  • Participants are questioning the discrepancy in the sign convention for work done by a gas during expansion, noting that AP Physics indicates negative work while textbooks suggest it is positive. There are discussions about the conventions used and the implications of these signs in equations.

Discussion Status

Some participants have provided insights into the conventions of work, indicating that when a gas expands, it is typically viewed as doing work. However, there remains uncertainty about the differing interpretations between AP Physics and textbooks, and no consensus has been reached on the underlying reasons for these differences.

Contextual Notes

Participants express concern about the implications of the sign conventions in the equations, particularly in relation to the first law of thermodynamics. There is an acknowledgment that understanding the signs is crucial, but the specific reasons for the discrepancies remain unclear.

Abelard
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Confuses me very much. AP Physics specifies that when gas expands, negative work has been done. But most textbooks say that it's positive work.

Could anyone explain the discrepancy here?
 
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It's usually a convention that is used.

Normally, when a gas expands, you would say that the gas is doing work

if the gas contracts, you would say that work is being done on the gas.
 
I was worried about the sign when the gas expands. Why do AP and textbooks differ in signs?
 
Abelard said:
I was worried about the sign when the gas expands. Why do AP and textbooks differ in signs?

Not too sure, but you just need to know what the signs mean in the equations.

e.g. first law of thermo dynamics

Q12-W12= ΔE

W12 happens to be the work done by the gas
 
Thanks a lot though. So the work done by the gas is positive when it expands.
 
Abelard said:
Thanks a lot though. So the work done by the gas is positive when it expands.

Yep, that's the normal convention used.
 

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