Slide 2 of 12
Steady flow isnít the same thing as constant velocity: If you were to move along with a small piece of fluid in steady flow, you might find its motion to be complex and non-uniform. On the other hand, the instantaneous velocity of the fluid that passes any fixed point in the fluid will be constant. It is the flow pattern that is fixed.
For example, if you were in a barrel moving with the water going over Niagara falls, your velocity would be far from uniform; yet, at any given point in the falls, the speed and direction of the water passing that point doesnít change much with time, because the flow is pretty steady.