Path lines are the lines traced by fluid particles to show its movement in the following direction. This trajectory motion of fluid particles can be described using Lagrangian method of fluid flow.

For example, path traced by the smoke particles of cigarette follow path line.

Now,

Let us consider the Fig. 4.2 where P_{1}, P_{2} and P_{3} are three different fluid particles of fluid flow at time t_{1} to reach another position at time t_{2} shows the path lines made by certain particles.

**Note:**

Suppose the fluid flow is steady. In this condition, the path lines will be identical to the stream lines.

**Links of Previous Main Topic:-**

- Vapour compression refrigeration cycle introduction
- Basic fluid mechanics and properties of fluids introduction
- Fluid statics introduction
- Manometers measurement pressure
- Fluid kinematics
- Lagrangian method for describing fluid method
- Eulerian method for describing fluid method
- Lagrangian relationship from eulerian equations
- Steady and unsteady flows
- Uniform and non uniform flows
- Stream line
- Path lines

**Links of Next Mechanical Engineering Topics:-**