- 2070 Magh · 4 marks
Thermodynamic work vs mechanical work
Short answer
Thermodynamic work is any interaction whose sole effect outside the system could be raising a weight; it is a path function and includes all forms of energy transfer except heat. Mechanical work is force × displacement in direction of force, only one form. Thermodynamic work depends on system boundary choice.
Explain the concept of thermodynamic work and differentiate it with mechanical work.
Thermodynamic work
Work is done by a system on its surroundings if the sole effect external to the system could be reduced to the raising of a weight. It is an interaction at the boundary, energy in transit, and a path function. Examples: gas expansion against a piston, electrical work done by a battery, shaft work of a turbine, stirring work. It does not need a visible force and displacement.
Mechanical work
Work is done when a force moves its point of application in the direction of the force: W = ∫ F · dx. It is only one form of work.
| Basis | Thermodynamic work | Mechanical work |
|---|---|---|
| Definition | Effect at the boundary that could be reduced to raising a weight | Force × displacement in the direction of force |
| Scope | Includes mechanical, electrical, magnetic, chemical, etc. | Only force and displacement |
| Dependence on system | Depends on the choice of system boundary | Depends only on force and displacement |
| Typical expression | δW = P dV, δW = V I dt (electrical) | δW = F dx |
| Example | Current through a resistor if the battery is the system | Pushing a box on the floor |
For example, electrical work is done on an electric motor that drives a pump, even though no force or displacement can be seen at its electrical terminals.
✓ Answer checked by Claude Opus 5.5 (high effort)
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