As this blog is designed to follow my line of study in Fluid Dynamics, it would make sense to write about the first lecture that we had.
We were questioned as to the whereabouts of two suspended ping pong balls if a stream of air was blown in the space between them. Naturally one would imagine the balls to go in opposing directions, however they surprisingly moved towards each other. This set minds racing as to how this can work, and what else this applies to.
Having recently helped at the university’s science and technology showcase, I was shown similar experiments. If a straw is placed through a cotton reel, with plasticine concealing the holes surrounding it, and a piece of paper is placed on the bottom, if you blow hard enough on the straw, the paper sticks to the reel.
Similarly, with a piece of paper, hold it near your mouth and blow across the top, the paper will rise.
How?
The faster the fluid flow, the lower the pressure, and equally, the slower the fluid flow, the higher the pressure. The best demonstration for this is an airplane’s wing as you can see in the diagram here:
When two particles separate at the front of the wing, the top one has to move faster to match the one below. The shape of the wing is an airfoil, and this is the optimum shape for a plane wing, because it allows the pressure above to be lower, and the pressure below to be higher, therefore creating lift. As an airplane increases its speed, the fluid flow is faster, and therefore lift is created.
This is the Bernoulli principle. The idea that an object will cling to the lower pressure, and therefore sometimes will act quite opposite to what you would originally think.I always find visual aids useful in understanding principles in mathematics, and having seen how objects are affected has sparked my interest for the future.
Sources:
University of Plymouth Science and Technology showcase
http://hyperphysics.phy-astr.gsu.edu/hbase/pber.html
Images courtesy of:
My Fluid Dynamics Blog 