Skip main navigation

Resisting pressure-vacuum

The pressure in mechanical work or P-V work

The pressure in mechanical work or P-V work

The magnitude of mechanical work or the P-V work is the force F, multiplied by the displacement dx through which the system boundary moved

[delta W=Fquad dx F=bar { P } cdot A delta W=bar { P } cdot Adx=bar { P } cdot dV]

(blacklozenge) Be careful! The pressure (bar { P }) here is the “resisting” pressure, NOT the system pressure P.

If your system is a gas with pressure P, and it expands against vacuum by volume ΔV, work done by the system is “ZERO” since the resisting pressure is zero

$$ delta W=-bar { P }quad dV=0 $$

This article is from the free online

Thermodynamics in Energy Engineering

Created by
FutureLearn - Learning For Life

Reach your personal and professional goals

Unlock access to hundreds of expert online courses and degrees from top universities and educators to gain accredited qualifications and professional CV-building certificates.

Join over 18 million learners to launch, switch or build upon your career, all at your own pace, across a wide range of topic areas.

Start Learning now