Question

Which of these changes do not contribute to a change in momentum in the momentum equation?

(a) Surface fluxes

(b) Surface forces

(c) Body forces

(d) Rate of change term

I have been asked this question at a job interview.

This interesting question is from Incompressible Flows topic in chapter Incompressible Flows & Compressible Flows of Computational Fluid Dynamics

Answer 1

Correct answer is (d) Rate of change term

For explanation I would say: The rate of change term represents the change in momentum in the momentum equations. This change is affected by any changes in the surface fluxes, surface forces and body forces acting on the element.