Work positive or negative

[Jessica Li 4F]

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

[nehashetty_2G]

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]

^^ 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]

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]

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]

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.