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

Our purpose is to transform access to education.

We offer a diverse selection of courses from leading universities and cultural institutions from around the world. These are delivered one step at a time, and are accessible on mobile, tablet and desktop, so you can fit learning around your life.

We believe learning should be an enjoyable, social experience, so our courses offer the opportunity to discuss what you’re learning with others as you go, helping you make fresh discoveries and form new ideas.
You can unlock new opportunities with unlimited access to hundreds of online short courses for a year by subscribing to our Unlimited package. Build your knowledge with top universities and organisations.

Learn more about how FutureLearn is transforming access to education