## Work Done On or By System

Amanda Mac 1C
Posts: 58
Joined: Fri Sep 29, 2017 7:05 am

### Work Done On or By System

How do you differentiate between whether work is done ON a system or BY the system?

Yashaswi Dis 1K
Posts: 56
Joined: Fri Sep 29, 2017 7:04 am

### Re: Work Done On or By System

Work done by system: negative sign for work

Work done on system: positive sign for work.

Another way to help differentiate the two:
Think of the equation: w= -P * (delta V).
---->If volume expansion occurs, then final volume minus initial volume is going to be positive so with the negative sign in the front of the equation, work will be negative and so the system DID work on the surroundings.

---->If volume compression occurs, final - initial volume (delta V) will be negative, so when you have the negative times the negative sign in the front of the equation, you get a positive value for work, so work was done ON the system.

A friend told me her analogy to help her remember: doing work by herself (the system of interest) requires work and so that can be negative for her whereas when someone else (the surroundings) does something for her, she feels good.

Hope that helps! Good luck for your test!

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