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Science Activity -- "I can't take the pressure."

This simple and effective experiment about air pressure has a big “wow” factor for children (and adults) of all ages.

Materials needed: • Two straws (clear work best) • One clear drinking glass

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Instructions:

  1. Fill a clear drinking glass close to the top with any liquid (water works fine, but a colored liquid allows you to see it a bit easier.)
  2. Hold one straw in the glass straight up and down (vertically).
  3. Hold the second straw horizontally at the top of the vertical straw.
  4. Now blow hard through the horizontal straw so that the air stream is flowing across the top of the straw that is in the water.

The water will move up the straw.  The faster the air blows across the top of the straw, the higher the water will rise up into the straw.

Pictorial direction for step one

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How does it work?
There are two scientific principles at work in this experiment.

1.  Air pressure – As you may know, air is made up of molecules that are in constant motion.  As these molecules push against any object, they exert a force or pressure on that object.  At sea level, this pressure is approximately 15 psi (pounds per square inch.)  This pressure is pushing down on the water both outside and inside the straw.

Pictorial direction for step two

2.  Bernoulli’s principle – An 18th century Swiss scientist named Daniel Bernoulli discovered that fast moving air (like the air blowing across the top of the straw) has less pressure than slower moving air.  The air pushing down on the water in the cup is 15 psi, but the fast moving air going across the top of the straw is less than that (say 14 psi).  The greater pushing force pushing down on the water outside of the straw forces the water higher up on the inside of the straw.

Pictorial direction for step three

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Practical applications of Bernoulli’s principle
There are many practical applications of Bernoulli’s principle such as the carburetor in a car engine and lift on airplane wings.  This principle also helps us understand why certain things happen.  For example, in a hurricane, windows blow out away from the house.  The reason for this is because the wind just outside the window is moving very fast (very low pressure), and the air inside the house is not moving (higher pressure).  Therefore, the high air pressure in the house pushes the windows out.
 
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Cathy Duffy Review

"All this makes the intermediate advanced kit an excellent choice for those looking for a hands-on physical science course."
   
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