Question

Which of the following is correct?

(a) pathlines are concerned with a number of particles at the same instant and streamlines with a particular particle at successive instants of time

(b) pathlines are concerned with a particular particle at successive instants of time and streamlines with a number of particles at the same instant

(c) both pathlines and streamlines are concerned with a number of particles at the same instant

(d) both pathlines and streamlines are concerned with a particular particle at successive instants of time

I had been asked this question in my homework.

This intriguing question comes from Types of Flow Lines topic in portion Kinematics of Flow and Ideal Flow of Fluid Mechanics

Answer 1

Right answer is (b) pathlines are concerned with a particular particle at successive instants of time and streamlines with a number of particles at the same instant

Easy explanation: A pathline is the path followed by a particle in motion whereas a streamline is an imaginary line within the flow such that the tangent at any point on it indicates the velocity at that point. Thus, pathlines are concerned with a particular particle at successive instants of time and streamlines with a number of particles at the same instant.