positive/negative work

[Yuzhe Yuan]

Hi,

Did Dr.Lavelle mean "work done by the system" is equivalent to "work done on the system"? This seems kind of counterintuitive to me since I thought they meant the opposite. Can someone explain the exact meaning of these terms and the positive/negative signs in calculating work?

[Emily Ngo 1E]

Hi Yuzhe,
"work done by the system" happens when it exerts some force and expends some energy. On the other hand, "work done on the system" is when an external force is applied to the system, increasing its internal energy. A negative sign indicates a system is losses energy while a positive sign indicates a system gains energy (At least this is the case for the equation w = -PdeltaV). Let me know if you need further clarification.

[Ashley Wilson 2L]

When the system does work on the surroundings, the work is positive since energy is exiting the system. When the surroundings do work on the system, the work is negative since energy is added to the system.

Here's a diagram that explains this better! https://www.researchgate.net/profile/Ba ... ndings.png

[Noa Popko 3I]

When work is a positive value, that means that that the system did work on the surroundings. When work is a negative value, that means work was done on the system by the surroundings.

[Katherine Li 1A]

"Work done by the system" is when the system expends energy by exerting force on somethings else. This is when work is negative. "Work done on the system" is when something else applies energy or force to the system. This is when work is positive. The system can change depending on what you are considering the system for a specific problem, which is why both those descriptions might apply to the same thing in a reaction, depending on what you are focusing on.