Bernoulli’s equation

Conclusion

In a forthcoming article we will look at some examples of the application of Bernoulli’s equation. From this article I hope the reader has developed a feel for some aspects of fluid motion: the concept of a fluid particle, the two types of fluid acceleration and how motion in one part of the fluid causes motion in other parts of the fluid. Bernoulli’s equation can be viewed in two ways. One as Newton’s second law applied to a line of fluid particles in a stream-tube. The second as a statement of energy conservation: the change in gravitational potential energy plus the change in kinetic energy is equal to the work done by the pressure forces.

Finally, one can observe fluid motion in small streams, or on a roadside after rain, aided by small leaves or other floating debris which are carried by the flow and act as tracers. A leaf accelerates when a passage through which the water is flowing narrows; or it ‘senses’ and changes direction when it approaches an obstacle like a small stone. Sometimes one sees a thin layer of oil on top of the water and then the relative motion or distortion of the flowing fluid can be observed. These tracers simply show what the fluid particles below them are doing.