How to tell when work is done by or done on the system?

[Mia_Renna_1L]

How do we tell work is being done by or done on the system? How does this correlate to the sign of work (negative or positive)? How does this relate to expansion?

[Kiara Mauro 1D]

If system volume expands against a force, work is done by the system. Also, if work is done by the system it is positive. If system volume contracts under a force, work is done on a system. When work is done by the system, it's negative.

[Alyssa Gates 1H]

I read that when work is done ON the system it is positive, so this is when the system volume contracts under a force. When work is done BY the system it is negative, this happens when the system volume expands against a force.

[Itxhel Jimenez 1B]

How do we tell work is being done by or done on the system? How does this correlate to the sign of work (negative or positive)? How does this relate to expansion?

Work is done on a system when there is a difference in initial energy and in final energy.

[Lale Kacharian 2K]

When the work is a negative value, that means that the system itself is the one doing the work. Therefore volume decreases.

[Howard Chu 1H]

Work is negative when work is being done by the system, and work is positive if it is done on the system. For gas, compressing is work being done on the system, and the system expanding is an example of work being done by the system.

[Zain Syed 1E]

When work is done on the system, then it would be positive and the gas inside would compress decreasing the volume. When work is done by the system, then it would be negative, the gas inside would expand, and the volume would increase.

[Julia Scheithauer 1J]

If the volume of the system expands against an external pressure or force, then the work is positive and is done by the system. If the system compresses due to external pressure or force put on the system by the surroundings, then the work is negative and work has been done on the system.

[Dominic Pham 3A]

In relation to delta U, we know that a system has done work when its internal energy decreases as it is giving off energy (assuming no heat transfer). Conversely, we know that a system has had work done on it when the internal energy increases as it is gaining energy (once again assuming no heat transfer).