Bernoulli's Floating Ball

Floating on air.

 

 

 

Category - Solids, Liquids & Gasses

Key Idea - Bernoulli's Effect

 

Purpose - A spectacular way to demonstrate Bernoulli's principle.   

 

 

The ball floats in midair.
Nature -  Demonstration with student assistance.
Materials -  A vacuum cleaner that can be set to blow (or a hair dryer can be used for a smaller scale demo), a Styrofoam ball (can be purchased from craft supply shops), a small inflatable beach ball, a table tennis ball, and balloon, a small hoop of wire that will fit around the smaller balls, retort stand with clamps
Method - 
  1. Remove the brush end from the vacuum cleaner to be left with a bare pipe.
  2. Set the vacuum cleaner to blow, and use the stand to position the pipe to blow straight up into the air.
  3. Turn on the vacuum cleaner and balance the Styrofoam ball in the middle of the air stream.  You should find that it wobbles a bit at first, but the settles to a smooth float above the pipe.
  4. Use the wire hoop to show that the ball is completely suspended.
  5. Try it with the other balls.  Where do they float comparatively?
  6. Unhook the pipe and hold it at a slight angle. Does the ball still float?  How Much of an angle can it take before the ball falls?
  7. Gentle grab the ball and pull it out of the air stream and feel the pressure trying to pull it back.
Safety - Nil
Explanation - Bernoulli's principle says that faster moving air has a lower pressure than slower moving air.  As the ball falls out of the stream of air, the moving air straight up is able to move faster than the air moving around the ball.  It therefore has lower pressure and pulls the ball back into the stream.  The "suck" is so strong that it can even hold the ball at an angle.  
Notes - The Bernoulli principle is the reason why an aeroplane can fly.  The wing is shaped in such a way that the air moving over the top surface travels faster than that under the wing.  It is therefore at a lower pressure - which gives the wing lift.