User:Mr swordfish/Bernoulli principle/1
False Demonstrations of Bernoulli's Principle
There are several common classroom physics demonstrations that are incorrectly ascribed to Bernoulli's Principle. One involves holding a piece of paper horizontally so that it droops downward and then blowing over the top of it. As the demonstrator blows over the paper, the paper rises. The purported explanation is that the faster moving air has lower pressure, and although this explanation is offered by otherwise reputable sources[1][2] , peer-reviewed physics articles show that this explanation is incorrect[3]
The problem with this explanation can easily be seen by blowing on the bottom of the paper - were the deflection due to speed differences one would expect the paper to deflect downward.
Since Bernoulli's principle only applies along a streamline, it is false to make a connection between the flow on the two sides of the paper using Bernoulli’s equation.
References
- ^ Smithsonian National Air and Space Museum http://howthingsfly.si.edu/sites/default/files/attachment/BernoulliBrain-Teasers.pdf
- ^ Univ. of Minnesota School of Physics and Astronomy http://www.physics.umn.edu/outreach/pforce/circus/Bernoulli.html
- ^ Blowing over a piece of paper does not demonstrate Bernoulli’s equation. While it is true that a curved paper lifts when flow is applied on one side, this is not because air is moving at different speeds on the two sides... It is false to make a connection between the flow on the two sides of the paper using Bernoulli’s equation.