The_Bernoulli_Principal__Blasters,_Planes,_and_Hurricanes

The Bernoulli Principal: Blasters, Planes, and Hurricanes In 1738 a Dutch-Swiss mathematician by the name of Daniel Bernoulli published the relationship of a fluid’s pressure, speed, and potential energy. Bernoulli demonstrated that an increase in the speed of a fluid will result in a decrease of pressure or it’s potential energy. Though many non-physicians might find this relationship to be irrelevant to them; I want to prove them otherwise and show that if it weren’t for Bernoulli’s Principle our lives would be different, and to some much more complicated. The principles of fluid described by Bernoulli are actually quite simple to understand when we break it down into its basic form. The exhibit that I analyzed at the Ann Arbor Hands-On Museum was titled “The Bernoulli Blast” and it did exactly that. It showed, in its most basic form, the concept behind these principles of pressure. The exhibit is properly set up to facilitate the understanding of Bernoulli’s Principle. What we have before us is a long cylinder tube that lies on top of an aspirator pump. On both sides of the tube, there is an opening that allows high-pressurized air to enter the tube. At the bottom of the tube, there is another opening that enables us to slide our lightweight plastic ball through so that it now lies on top of the aspirator pump and within the tube. To operate the exhibit we must first place the ball in the proper launching location. Once the ball is placed in the tube, one must press the indicated button, this causes the device to channel air through an aspirator, which through a combination of the Bernoulli principals and the equation of continuity, this leads, the air through a narrower area and increases the speed of air and it lowers its air pressure. Because the ball is round, the low air pressure moves around the surface of the ball to the top of the ball creating a patch of lower air pressure above it. It is this that causes the ball to generate lift and be launched into the tube. Recall that the tube has a hole on both sides that allows for the flow of high-pressure air into the tube. The area above the ball is acting as a (partial) vacuum, thus creating suction on the plastic ball. The definition of a vacuum is to have zero pressure, meaning extremely low pressure. There is a vacuum that is created above the ball, which means that the pressure above (around) the ball is lower than the pressure below the ball and anywhere else in the room. As we learned in class from the Bernoulli Principal, we know that air flows from high pressure to low pressure. Thus the air underneath the plastic ball is trying to rise to the lower pressured atmosphere when the it is in the tube and as it does that we witness the ball lift along with it. Once the ball reaches the top of the tube it hovers until the aspirator lift is turned off. The reason for this is because the air that is being blown by the aspirator has created lower air pressure above (circling around) the plastic ball and the air in the room has a higher pressure, it is that higher pressure that prevents the ball from falling back down the tube or in either direction. Now that I have described how the exhibit functions in respect to the laws of physics, I would like to move on and analyze how the concepts of these principals apply to our lives. When Bernoulli conducted his tests he did it by using a fluid in it’s liquid state, although the principals remain the same, I just wanted to quickly clarify that the Bernoulli Blaster exhibits the principals for when the fluid is in its gaseous state. I would like to demonstrate a few practical uses of the Bernoulli principal, by demonstrating how it works with the concept of lift in an airplane wing and with a tornado and its effect. Both of these are examples of when fluid is in its gaseous state. The design, both shape and size, of an airplane’s wing is crucial for the airplane to generate enough lift during takeoff and to maintain in the air. We already know that high pressure wants to move to low pressure, but what does that mean for a wing on a plane' When the plane is merely taxing the airplane is streamlining, meaning that there are no forces of lift acting on it, the airflow flows horizontally across the wing and nothing happens. However when the pilot of the plane tilts the nose of the airplane up, creating an angle of attack we see the airflow take a different course. The airstream continues to travel about horizontal to the wing as it did when the angle of attack was zero but it slowly develops a different shape. The airstream is now splitting into two different airflows that aren’t symmetrical, with one half going over the tilted wing and the other going under it. As the streamlines split, each will bend twice, once up and once down. From the reading we know that as the airstream bends towards the wing the pressure near the wing is below atmospheric pressure and the exact opposite is true when the airstream bends away from the wing (p. 168). Although both airstreams extract nearly equal and almost canceling pressure changes, the bottom airstream makes a sharp bend up and around the end of the wing as it tries to follow its airflow. This upward “kink” creates an unstable vortex that the wing must then adapt to. Once it has adapted to the new airflow with the vortex we consider it to be in the Kutta Condition. Thus with this new patter of air the airstreams that flow atop the wing have longer streams and bend towards the wing, generating a higher speed and a lower pressure. While the airstreams below the wing have a shorter airstream and travel at a slower speed, meaning it has a higher pressure. As we saw from the “Bernoulli Blast” exhibit and from our classroom labs pressure flows from high to low. So if the angle of attack is creating low pressure on top of the wing and high pressure below it we can deduce that the wing will generate lift as the high pressure tries to rise. Before moving onto the next application of the Bernoulli principal I’d like to comment on the shape of the plane’s wing. In the “Bernoulli Blast” exhibit we used circular plastic balls, the fact that the balls were plastic is what made the exhibit function. Due to the shape of the balls we know that the air is able to flow around it and create the low-pressure patch on top of the ball. If we had tried to use a block the results would be much different, as the airstream would have had difficulties in making it around the block. The same sort of concept can be applied to the wings of the plane, the more curvature a wing has the more lift it can generate. This is why large commercial planes have flaps that extend out and down, these flaps elongate and make the wings a tad more round, these flaps are mostly used during take off. Tornados and hurricanes are very destructive because of the Bernoulli Principal. As we all know both tornados and hurricanes move and spin at a very rapid velocity. From our understanding of the Bernoulli Principal we can deduce that the pressure within the storm is lower than the surrounding pressure. So what does that mean for the poor house that is along its path' Well if the storm is moving at fast enough speed and lets say the roof of a given house is of low quality, then empirical evidence has shown that the roof will most likely be lifted off of the house. This happens because the pressure inside the house is in normal atmospheric pressure. When the normal pressure collides with the low pressure generated by the tornado, the tornado exerts a lift force on the roof of the house, just as wings and ball from the exhibit did. Just when you thought the problem was over, look up to see your roof falling from the sky right back onto your house. What has happened here is that once the roof is lifted from the house, the pressure no longer differs, and if there isn’t a difference in pressure there no longer is any lift, thus resulting in the roof coming crashing down. This is much different then our analysis of the “Bernoulli Blaster” where the ball floated on top of the tube. The difference is that the ball always had the difference in pressure to withstand it from falling, while the tornado eliminates that pressure difference shortly after lifting it up from the house because the pressure is equalized. As we have seen the principals observed by Daniel Bernoulli over 200 years ago are still in use today, and some more than others have very practical application to our lives. Some of its more practical uses I omitted because even though it uses the Bernoulli principals it doesn’t relate as much to the “Bernoulli Blast” exhibit. The use of water towers is a perfect example of the Bernoulli equation as well but it uses it in its liquid form instead of its gaseous form. If it weren’t for his principals, many New Yorkers would be left without water because we would not know how to manipulate the pressure to have it rise to the desired height. All in all Bernoulli equations surround us everywhere we go, whether it’s the small fan inside your bathroom that vents out the hot air or the large jet engines of an airplane, the principals remains the same as those observed in the “Bernoulli Blast” exhibit at the Ann Arbor Hands On Museum. The image illustrates a basic analysis of how wings generate lift. I previously explained that lift is created when the two airstreams that are separated bend in opposite directions and produce opposing pressure. The flow of the airstream on the bottom bends so that it has a higher pressure and the airstream on top bends so that its pressure is lower. Thus from the principals of Bernoulli we know that the high pressure will want to move to lower pressurized air thus creating what we know as lift. This image demonstrates the relationship between velocity and pressure. It basically shows the Bernoulli Equation and it shows how it is applied. As we can see velocity is greatest when the fluid is traveling thorough a more narrow space. According to the Bernoulli equation to keep everything equal we deduce that the pressure in the narrower region must be lower than the pressure in the wider region. This final image depicts how a hurricane can lift a roof off of a house. It shows that the pressure inside the house is at normal atmospheric pressure which is much higher when compared to the outside moving air pressure. Thus if the winds are strong enough it has been proven that the hurricane will actually be able to lift the roof off. Even if it doesn’t lift the roof, it is still producing and upward force on it. Bibliography Unknown., “Bernoulli and Newton”. 10. Dec 2009 http://www.grc.nasa.gov/WWW/K-12/airplane/bernnew.html. Heckert, Paul. “Bernoulli’s Principle and Storms”. 16 May 2007 http://physics.suite101.com/article.cfm/bernoullis_principle_and_storms/ Heckert, Paul. “Bernoulli’s Principle Example” 9 Mar 2007 http://physics.suite101.com/article.cfm/bernoullis_principle_examples Unknown., “Bernoulli’s Equations” http://hyperphysics.phy-astr.gsu.edu/Hbase/pber.html Unknown., “Bernoulli’s Principle” 30 Nov 2009 http://www.allstar.fiu.edu/aerojava/pic3-2.htm Unknown., “Bernoulli’s Principle” US Centennial of Flight Commission http://www.centennialofflight.gov/essay/Dictionary/bernoulli/DI9.htm