Page 1 of 1

### Work sign convention

Posted: Sun Feb 10, 2019 8:05 pm
Can someone explain if work is done on a system, do we use the positive or negative sign? What about for work done by a system?

### Re: Work sign convention

Posted: Sun Feb 10, 2019 8:11 pm
When work is done by the system the value you are going to get will be negative and when work is done on the system the value you will get will be positive. You shouldn't really have to worry about whether or not to put a negative because the determining sign will be a part of your equation you use. For example
w= -Pex(Delta V).

### Re: Work sign convention

Posted: Sun Feb 10, 2019 8:21 pm
You can also think of it in terms of energy. When energy is transferred to a system by doing work, the internal energy of the system increases and w is positive. In the same manner, when energy leaves the system as it does work, the internal energy of the system decreases and w is negative. (This is from 4A.2 in the textbook)

### Re: Work sign convention

Posted: Sun Feb 10, 2019 8:49 pm
W < 0 when work is done by the system
W > 0 when work is done to the system