It is an imaginary line such that when a tangent is drawn at any point it gives the
velocity of the fluid particle at that point and at that instant. Fig. 8 Stream lines
Eg: Path traced by the flow when an obstruction like, a sphere or a stick is kept during its motion. The flow breaks up before the obstruction and joins after it crosses it.
It is that imaginary line that connects all the fluid particles that has gone through a point/section over a period of time in a fluid motion.
It is an imaginary tube formed by stream line on its surface such that the flow only enters the tub from one side and leaves it on the other side only. No flow takes place across the stream tube. This concept will help in the analysis of fluid motion.
Variation of a Property along any given direction
If P is a Property at any point, then the property at any other location along x
direction at a distance dx is given by
Fig. 12 Variation of a property along x direction
New Property = Old Property + slope x Old Property x distance