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Bernoulli’s Principle

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1 Bernoulli’s Principle
To understand Bernoulli’s Principle, think about what happens when a a fluid such as air or water moves. Think about what happens if you hold a plastic spoon in a stream of running water. You might predict that the spoon would be pushed away by the water. But it is not. Surprisingly, the spoon is pushed toward the stream of water. The behavior of the spoon demonstrates Bernoulli’s Principle.

2 Daniel Bernoulli The Swiss scientist Daniel Bernoulli found that the faster a fluid moves, the less pressure the fluid exerts. Bernoulli’s principle states that the pressure exerted by a moving stream of fluid is less than the pressure of the surrounding fluid. The water running along the spoon is moving but the air on the other side of the spoon is not. The moving water exerts less pressure than the still air. The result is that the greater pressure of the still air on one side of the spoon pushes the spoon into the stream of water.

3 Another Example If you blow above a sheet of tissue paper, the paper rise. Moving air blown over the tissue paper , the paper will rise. Moving air blown over the tissue paper exerts less pressure than the still air blown the paper. The greater pressure below the paper pushes it upward.

4 Objects in Flight Bernoulli’s principle is one factor that can help explain flight - from a small bird to a huge airplane. Objects can be designed so that their shapes cause air to move at different speeds above and below them. If air moves faster above the object, pressure pushes the object upward. But if air moves faster below the object, pressure pushes it downward.

5 Bernoulli’s Principle at Home
Bernoulli’s principle can help you understand many common occurrences. For example, you can sit next to a fireplace enjoying a cozy fire thanks in part to Bernoulli’s principle. Smoke rises up the chimney partly because hot air rises, and partly because it is pushed. Wind blowing across the top of the chimney lowers the air pressure there. The higher pressure at the bottom then pushes air and smoke up the chimney.

6 Take a look… Turn to page 99 and lets read Exploring Wings and how Bernoulli’s principle helps explain how air moving around a wing produces a force.

7 Figure 20 Turn to page 100 and lets read how Bernoulli’s principle helps us understand how an atomizer works.

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