Work positive or negative


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Jessica Li 4F
Posts: 115
Joined: Fri Aug 09, 2019 12:16 am

Work positive or negative

Postby Jessica Li 4F » Sat Feb 01, 2020 5:51 pm

How can you tell when work is positive or negative when calculating the internal energy, such as in 4B.5?

nehashetty_2G
Posts: 102
Joined: Thu Jul 25, 2019 12:15 am

Re: Work positive or negative

Postby nehashetty_2G » Sat Feb 01, 2020 6:27 pm

When the system does work on something outside of the system, it is negative work because they system is losing energy (ex. the piston moves out/expansion). When something else is doing work on the system, it is positive work because the system is gaining energy (ex. piston moves in/compression). I also think of it visually: When compression is occuring the molecules bump into each other more and therefore energy increases.

cassidysong 1K
Posts: 100
Joined: Fri Aug 30, 2019 12:15 am

Re: Work positive or negative

Postby cassidysong 1K » Sun Feb 02, 2020 4:01 pm

^^ what they said; if the system is doing work it's negative, if work is being done on the system then it's positive

charleejohnson1L
Posts: 99
Joined: Fri Aug 30, 2019 12:17 am

Re: Work positive or negative

Postby charleejohnson1L » Sun Feb 02, 2020 4:02 pm

the way I think about it is to imagine yourself as the system. if you're doing work, you're doing to be using energy (negative value) and if work is being done on you, that's energy saved (positive value). I hope this helps :)

TimVintsDis4L
Posts: 104
Joined: Sat Aug 17, 2019 12:17 am

Re: Work positive or negative

Postby TimVintsDis4L » Sun Feb 02, 2020 4:05 pm

Can we think of work as either exothermic and endothermic. The work can be in the form of heat so would that be a valid statement.

Andres Merlos 2L
Posts: 46
Joined: Wed Sep 18, 2019 12:17 am

Re: Work positive or negative

Postby Andres Merlos 2L » Sun Feb 02, 2020 6:16 pm

If the system is doing work, you would have a negative value because energy is being used. This is because the system loses something, energy, resulting in the negative value we see. If work is being done on the system, you would receive a positive value because the energy is directed towards the system.


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