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

Click For Summary
SUMMARY

The discussion centers on the thermodynamic identity expressed as dU = τdσ - pdV, specifically analyzing the implications of compression on work done within a system. When compression occurs, the volume change (dV) is negative, resulting in positive work done on the system, as indicated by the term -pdV. The identity can be reformulated to express work done by the system by simply switching the sign, emphasizing the importance of consistency in sign usage throughout calculations to maintain clarity and correctness.

PREREQUISITES
  • Understanding of thermodynamic identities
  • Familiarity with the concepts of work and energy in physics
  • Knowledge of pressure-volume relationships in thermodynamics
  • Basic grasp of calculus as it applies to differential equations
NEXT STEPS
  • Study the implications of the first law of thermodynamics
  • Explore the concept of work done by and on a system in greater detail
  • Investigate the role of pressure and volume in thermodynamic processes
  • Learn about the applications of thermodynamic identities in real-world systems
USEFUL FOR

This discussion is beneficial for physics students, thermodynamics researchers, and engineers involved in energy systems who seek to deepen their understanding of work and energy relationships in thermodynamic processes.

eep
Messages
225
Reaction score
0
In terms of the thermodynamic identity:

[tex] dU = {\tau}d{\sigma} - pdV[/tex]

the term for the work done on the system ([itex]-pdV[/itex]) 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.
 
Science news on Phys.org
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.
 

Similar threads

Undergrad Sign convention on work done to a closed system containing gas
  • · Replies 5 ·
Replies
5
Views
4K
Undergrad Understand the Thermodynamic Identity: Is This Correct?
  • · Replies 3 ·
Replies
3
Views
2K
Undergrad Work in hydrostatic system in cylinder with piston: P_int or P_ext?
  • · Replies 5 ·
Replies
5
Views
2K
Undergrad Meaning of average pressure in statistical mechanics
  • · Replies 1 ·
Replies
1
Views
2K
Undergrad Sign Convention for Work (In Thermodynamics)
  • · Replies 13 ·
Replies
13
Views
8K
Undergrad Yet again about (real) gas compression
  • · Replies 20 ·
Replies
20
Views
3K
Undergrad Thermodynamics: sign convention
  • · Replies 3 ·
Replies
3
Views
5K
Undergrad Graphical difference between adiabatic and isothermal processes.
  • · Replies 1 ·
Replies
1
Views
4K
Graduate Confused about use of external vs internal pressure in thermodynamics
  • · Replies 13 ·
Replies
13
Views
4K
Graduate Work done for isothermal process in terms of Helmholtz func
  • · Replies 3 ·
Replies
3
Views
2K