• Online Science Resources

    Online Science Resources
 

Whirly Tubes

  • Exploration

Activity Length: 

10 mins.

Resource Topic: 

  • Energy
  • Sound

Comments

I believe that the Bernouli

I believe that the Bernouli Principal does not apply here and that the air moves through the whirly tube due to centrifugal force.

Thanks, Mark

Thanks, Mark Centrifugal force isn’t really a kind of force. It’s a term used to describe, for example, the experience you have when you go around a corner in a car. Your body will move in a straight line unless something makes it turn; in this case, the car door pushes you around the corner and it feels like you’re “thrown to the outside”. The “thrown to the outside” feeling is what some people call “centrifugal force”. When you whirl the tube in this experiment, your hand is providing the force (officially called the centripetal force) that keeps the end of the tube moving in a circle. The air, on the other hand moves up through the tube and straight out the end. You can demonstrate this by holding the still end of the tube over a pile of tiny paper scaps. The scraps move up the tube and fly out the end. They aren’t being pulled in a circle at all – they’re being pushed through the tube by the higher pressure air at the still end. It’s the air moving through the tube, over the ridges, that creates the sound vibrations. You could try blocking the whirling end of the tube – do the little bits of paper still move into the tube? With the end blocked, the air in the tube is pulled in a circle. You are pulling on the tube, and the tube is pulling on the air. But although a molecule of air in the tube might feel “thrown to the outside” when the tube pushes it around the corner, you won’t hear any sound because the air isn’t moving through the tube.

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