7th Edition 4A3

[Jasmin Argueta 1K]

For this problem I'm very lost. Its discussing compressing air into a tire through the use of a pump. To get work the equation w=(-Pexternal)x(change in volume) is used. Where is the negative P coming from?

[Matthew Tran 1H]

There is a negative sign because the w, the work done by the system (the air inside the pump), is negatively proportional to its change in volume. That is, when the system expands, it does work and loses energy, and when it is compressed, work is being done on it and it gains energy.

[Jasmin Argueta 1K]

Thank you!