Stream Lines

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.

Streak lines

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.

Stream tube:

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