Regarding the definition of Work

[Abelard]

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?

 

[rock.freak667]

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.

 

[Abelard]

I was worried about the sign when the gas expands. Why do AP and textbooks differ in signs?

 

[rock.freak667]

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

 

[Abelard]

Thanks a lot though. So the work done by the gas is positive when it expands.

 

[rock.freak667]

Thanks a lot though. So the work done by the gas is positive when it expands.

Yep, that's the normal convention used.