Negative sign on work equation


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romina_4C
Posts: 100
Joined: Thu Jul 11, 2019 12:17 am

Negative sign on work equation

Postby romina_4C » Wed Jan 29, 2020 2:28 pm

Why is there a negative on the w = - P times delta V? Is there any situation where this would not be the case?

Tai Metzger 3K
Posts: 103
Joined: Sat Aug 24, 2019 12:17 am

Re: Negative sign on work equation

Postby Tai Metzger 3K » Wed Jan 29, 2020 2:29 pm

W will be negative if the system is doing work (expansion) and will be positive when work is being done on the system (compression). I hope this helps!

Veronica_Lubera_2A
Posts: 106
Joined: Sat Sep 14, 2019 12:16 am
Been upvoted: 1 time

Re: Negative sign on work equation

Postby Veronica_Lubera_2A » Wed Jan 29, 2020 3:20 pm

Yes, in expansion there will be a negative sign because the system is losing energy.

DanielTalebzadehShoushtari2A
Posts: 53
Joined: Fri Aug 02, 2019 12:16 am

Re: Negative sign on work equation

Postby DanielTalebzadehShoushtari2A » Wed Jan 29, 2020 4:08 pm

I agree with the above explanations in that the whole term for w is positive/negative depending on whether or not the system is expanding or being compressed. You can think of the negative sign in the formula in a different way: w stands for work being done on the system. In this way, expansion would make delta V positive, and work done on the system is negative (because work is being done by system instead). It works similarly for compression.
In this way, w can be put into the context of U = q + w and make sense because work being done on the system is part of the total energy that the system has.


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