Is the Work Done on a System Positive When There is Compression?

[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.

 

[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.