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Bernoulli's Principle
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| Does anyone know how Bernoulli's Principle of Hydrodynamics apply to our lives? Help plzzzz... |
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Re: Bernoulli's Principle
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by desertranger
on 2006-01-03 08:42:29
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Sure Lydia I can explain it for you. Bernoulli's principle states that a foil (wing) with a curved upper surface moving through any fluid medium, liquid or gas, causes the medium to move faster over the curved surface than the flat surface creating negative pressure also called a a partial vacuum, on the curved side the foil. Inflying we call this lift. In RL that's the principle that makes airplanes fly and what holds cars to the ground in a fast turn. In an airplane wing the curve is on the upper surface and on the fron side of the propeller. If I take my plane and start rolling down the runway at some point, ~82mph, the air (fluid medium) moving over the top of the wing is enough to create the lift (suction or partial vacuum) needed to overcome the force of gravity holding the plane down and I start my climbout. I can control how fast I climb by the angle of the wing and its relationship to the air moving over the wing. This is called the angle of attack or AOA. In normal flying at a constant speed with an AOA of 0 degrees, the forces of lift (curved wing), drag (resistance to the air), thrust, (the engines) and gravity balance each other so I maintain straight and level flight. If I increase the power settings on the engines air flows faster over the wing and the plane climbs or is pulled into the partial vacuum, and if I pull the throttle back so I fly slower and the air over the wings moves slower so gravity takes control and I descend. As long as the angle of attack (AOA) remains within the wings design parameters it will continue to provide lift. Exceed those parameters and the movement of the air over the surface is disturbed (turbulence) and you lose lift, called a stall. By controlling theshape of the wing, the AOA and the airspeed we can make the plane do what we want. If we bank the plane the lift pulls us to that side. If I put the plane on it's side like a fighter does and pull the stick back hard I literally fly around the corner making a very tight turn, called a break turn. Scenario: Landing a plane with Bernoullis principal. With all forces in balance we start to approach the runway from 2000 feet straight in from 5 miles away. As you approach the runway you have to maintain enough speed to keep the plane in the air without stalling (falling) about 77-79mph and maintain a controlled descent. With the throttle set to keep you at ~82mph you cross over the end of the runway and pull back on the wheel to increase the AOA and reduce the throttle at the same time tolower your airspeed slowing yourself down to just above stall speed and when you fall below the speed needed to keep you in the air (~77mph) you settle gently to the ground. If you did it right you stick it and roll to a stop in about 1000 ft. If your Rin you bounced a couple of times and used a lot more runway. Don't forget if I fly inverted (upside down) lift is pulling me toward the earth so I have to push the stick to dive away from the ground. It's really easy to fly. Just stay in the middle of the sky. Don't go to near the edge of the sky which is is easily recognized by the presence of buildings, trees and the ground or water.  |
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Re: Bernoulli's Principle
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by
on 2006-01-04 23:08:03 (edited 2006-01-04 23:08:38)
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flying is easy! i saw this mural on a wall someplace in Kyoto and thought it was deserving of 1.5 MB of space on my digital camera: 
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Re: Bernoulli's Principle
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| thank you soooo much!! |
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Re: Bernoulli's Principle
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by
on 2006-01-06 20:31:52 |
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What is that supposed to be a picture of?
Beware the quiet people,
You don't know their intentions
(small signatures are sooo much cooler since they don't annoy people trying to read through posts!) |
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Re: Bernoulli's Principle
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by
on 2006-01-06 22:18:59 |
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simple, it is a picture that illustrates clearly how easy it is to fly if you are a mechanized skeleton of fish.
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Re: Bernoulli's Principle
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Here is another quick application of Bernoulli’s principle: Imagine you have a pipe in which you have a flow of water. Of course, you will always have as much water that comes in pipe that water that comes out of it. Bernoullis first law says that all along your pipe, the total pressure (Pt), the flow (Q) and the total energy (E) are constant. If 1 is the entrance of your pipe and 2 the exit, you can write: Q1=V1.S1 Q2=V2.S2 V1 is the speed of water at the entrance, V2 at the exit. S1 is the section area of your pipe at the entrance and S2 at the exit. As I said, there is necessarily as much water that comes in your pipe than water that leaves your pipe. That is, Q1=Q2... Or if you prefer V1S1=V2S2 Now what’s the point? Well here it is: if you decrease the section in some part of your pipe, the speed of water will necessarily be faster. What are the applications? Well about a century or two ago, they made canon waters that could shatter rocks. They used them to dig the gold veins in mountains where the slopes where too steep. They inserted water in the canon from atop a small mountain in a huge pipe. As the pipe went down the mountain, its section progressively decreased, which would force the pressure to increase more and more, and the speed of water to increase. Another application is the Venturi tube, which enables to measure the speed of a plane: air passes in a pipe. Locally, we decrease the section and the pressure changes. By comparing with the pressure at the entrance, you can calculate your speed... Now, you have a phenomenon caled cavitation wich can occur, I'll try to explain briefly: Bernoulli says that to increase the speed, you have to increase the difference of pressure. A solution is then to locally DECREASE the pressure because the difference of pressure will increase. A water pump works this way. Problem is, you can vaporise a liquid if the pressure is to low. So in the place where the pressure is low, there might be some vapor bubbles that form themselves. It is what they call cavitation. The turbines of the pump might be severely damaged because of them. |
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Re: Bernoulli's Principle
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Oh, I was about to forget: in formula 1 races, it is Bernoulli that enable the cars to stay on the ground because of their shape. It works like the wings of a plane, but the other way around. In chemical processing, Bernoulli theorems are widely used to calculate the dimensions of pipes in manufacturing plants and reactors (how to transport efficiently a liquid, how to mix efficiently two liquids, what kind of pump, how powerful, how to avoid waste of good energy, etc.) |
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Re: Bernoulli's Principle
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hey lydia..do you wanna be a chemical/biochemical/civil engineer? i can tell you about them if you like.
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