this topic is from fluid mechanics and is about stream lines and streak lines along with diagrams....

1. A streamline is a path traced out by a massless
particle as it moves with the flow.
OR
A streamline is one that is drawn tangential to the
velocity vector at every point in the flow at a given
instant and forms a powerful tool in understanding
flows.

2. Stream lines

3. Explanation
A moving body causes the air to flow around it in definite
patterns, the components of which are called
streamlines.
 Smooth, regular airflow patterns around an object are
called laminar flow they denote a minimum of
disturbance of the air by the object’s motion through it.
Turbulent flow occurs when air is disturbed and
separates from the surface of the moving body, with the
consequent formation of a zone of swirling eddies in the
body’s wake.

4. Streak line
The locus of all the points that have gone through a given point
in a flow is called streak line.
 It concentrates on fluid particles that have gone through a
fixed station or point. At some instant of time the position of
all these particles are marked and a line is drawn through
them. Such a line is called a streak line

5. Streak line