Work for compression/expansion

[Melodie Oh 2A]

Can someone explain why the value for work is positive when it is compression and why it is negative when it is expansion??

[SantanaRodriguezDis1G]

The negative indicates that the system is losing energy

[Lindsay H 2B]

I like to think of it as how when something is compressed (like the air in the bicycle pump in problem 8.3) it means work is being done on the system, so the system gains energy (positive work). In an opposite scenario if the air in the bicycle pump were allowed to expand, the energy for the expansion comes from inside the system, therefore the system loses energy (negative work).