# Bernoulli demostrations

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DEMOSTRATION OF BERNOULLI’S PRINCIPLE.
UNIVERSITY OF MINNESOTA.

The relationship between the velocity and pressure exerted by a moving liquid is described by the Bernoulli's principle: as the velocity of a fluid increases, the pressure exerted by that fluid decreases.
Airplanes get a part of their lift by taking advantage of Bernoulli's principle. Race cars employ Bernoulli's principle tokeep their rear wheels on the ground while traveling at high speeds.

BERNOULLI’S PAPER LIFT

This is a simple demonstration dealing with Bernoulli’s Principle. The demonstrator will hold a piece of paper close to his lips, and blow across the top of the paper as it hangs down from his hands in front of his lips. The paper will respond by moving up, toward the stream of moving air. It wouldseem the paper would move away from the stream of air, but it does not. It moves toward the stream of air. This is shown in the diagrams below:

[pic][pic]

HOW IT HAPPENS
Bernoulli’s principle states that fluids in an area moving faster than the the surrounding area possess less pressure. Faster-moving fluid, lower pressure. (In general, fluids include liquids and gasses. Air is a gas and assuch is classified as a fluid.) When the demonstrator holds the paper in front of his mouth and blows across the top, he is creating an area of faster-moving air. The slower-moving air under the paper now has higher pressure, thus pushing the paper up, towards the area of lower pressure. Perhaps you have noticed, for example, that an empty mayonnaise jar in your sink with water in it will move in,directly under the water faucet as you turn on the water. This is the same thing as we observe here. The water that is moving possesses less pressure, and the jar is pushed toward that area by the water that is not moving which has greater pressure.

Instructions
Place the cardboard squares about four inches apart on several straws set parallel to each other so that theycan roll along on the straws. Place the two bottles on the two squares of cardboard. Direct a blast of air between the two bottles, and they will move toward one another, actually hitting into each other. See diagram.

[pic]
This is another demonstration of Bernoulli’s Principle where an area of higher speed fluid is used to lower the pressure and the visible movement of two plastic pop bottlesis used to show the results. Because empty
2-liter pop bottles are very light, they require very little force to move them if you can reduce the friction between them and the table. When you blow between the two bottles, it would seem that they would move apart, away from the blast of air. However, because of Bernoulli’s Principle, the pressure between the two bottles will be lower than thepressure on the outsides, causing a net force to be exerted on each bottle toward the other. Because you have reduced the friction between the bottles and the table top, they can move toward each other easily, demonstrating the force on each bottle towards the other. If the bottles don’t move on the first few tries direct the blast of air a little off the center line between the two bottles and sooneror later they will move easily together.
You have probably heard that standing too close to a railroad train as it passes can be dangerous. This is true because a moving train drags the air close to the cars along with it. This rapidly moving air, by Bernoulli’s principle will have a lower pressure than the still air a few feet away. The still air, having higher pressure, and being behind you ifyou are standing close will tend to push you toward the train. The effect is enough to actually move a person if you are not careful!

Air Jet and Ball

Instructions
Attach the thread (about 3 to 4 inches in length) to the pen barrel and to the ping-pong ball. Hold the pen barrel horizontally and blow vigorously through it while holding the ping-pong ball in line with the tube to get...