# Sign Convention Question

1. May 10, 2006

### eep

In terms of the thermodynamic identity:

$$dU = {\tau}d{\sigma} - pdV$$

the term for the work done on the system ($-pdV$) must be positive if there is a compression, in which case dV would be negative, correct? If one wanted to write the identity in terms of the work done *by* the system, you would simply switch the sign.

2. May 10, 2006

### dextercioby

It can be as easily the other way around (the work done on the system be negative), it only matters that the sign you choose be kept in all calculations, else what you'd be doing wouldn't make any sense.

Daniel.