w = -P*delta V

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Tiffany Chao 2H
Posts: 117
Joined: Fri Aug 09, 2019 12:17 am

w = -P*delta V

Postby Tiffany Chao 2H » Sun Feb 02, 2020 4:28 pm

This might be a dumb question, but is a negative sign in front of the P*delta V always there? And then if the volume is decreasing (so -deltaV), then work is positive?

Thanks

Skyllar Kuppinger 1F
Posts: 52
Joined: Thu Jul 25, 2019 12:16 am

Re: w = -P*delta V

Postby Skyllar Kuppinger 1F » Sun Feb 02, 2020 4:34 pm

Yes, the negative sign is always there. You're right that when the volume is decreasing, it makes the work positive. It's a convention thing-- when the system is being compressed, we say the work is positive. and when the system is expanding against something, we say the work is negative.

Jonathan Gong 2H
Posts: 105
Joined: Sat Jul 20, 2019 12:16 am

Re: w = -P*delta V

Postby Jonathan Gong 2H » Sun Feb 02, 2020 4:35 pm

Yes, w = -P*deltaV. If deltaV is negative then work will be positive. But, it is also important to consider what the question asks and what entity the work is being done on for the sign of work.

SarahCoufal_1k
Posts: 102
Joined: Thu Jul 25, 2019 12:17 am

Re: w = -P*delta V

Postby SarahCoufal_1k » Sun Feb 02, 2020 4:44 pm

yes, the negative sign is always there. When volume is decreased/compressed, delta V is negative so work is positive overall.
when volume is increased/expanded, delta V is positive and so w is negative overall. This is because when it is compressed, work goes into the system, and when it is expanded work leaves the system

Alondra
Posts: 36
Joined: Tue Feb 26, 2019 12:15 am

Re: w = -P*delta V

Postby Alondra » Sun Feb 02, 2020 11:40 pm

The negative sign is part of the equation. However, the work input or output differs depending on the pressure and change in volume.


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