People usually talk about pressure acting on such and such points like the pressure on a point at height h in a water tank or the air pressure on a point on the Earth's surface. But the definition of pressure is about a force acted upon an "area", not a point. Do people usually mean a differential area located somewhere in space and oriented in a certain way when they talk about a point or is there something I don't know?

  • $\begingroup$ Does this answer your question? Adding pressure $\endgroup$ Jun 16, 2022 at 18:20
  • 1
    $\begingroup$ The ratio of force to area is taken as the limit for an infinitesimal area. $\endgroup$ Jun 16, 2022 at 18:20
  • $\begingroup$ @Chemomechanics My question is mainly about if "pressure on a point" is a thing. $\endgroup$ Jun 16, 2022 at 18:28

1 Answer 1


The pressure is the one third the negative trace ($P=-\frac{\sigma_{11}+\sigma_{22}+\sigma_{33}}{3}$) of the stress tensor. Now, stress is defined as a force per unit area, and stress and pressure measurements must be conducted over a finite area. When we talk about the pressure (or stress) at a point, we're idealizing this area as infinitesimal; that is, we're taking the limit of the force-to-area ratio as the area is reduced toward zero.


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.