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Physics Demo: The Atomizer

A great proof of Bernoulli's principle is to fill a long narrow container (like a 100cc graduated cylinder) with small Styrofoam balls or puffed wheat. The challenge is to remove the objects from the cylinder without touching them or the cylinder.   Bernoulli's principle provides solution.

atomizer animation

When the container is just sitting there, the force from the slow moving air inside the container is equal but opposite to the force from the slow moving air on top of the container.  As a result the net force on each ball is just the weight of the ball, so they remain in the container.  When you blow air across the top of the tube, the faster moving air at the top applied less force on the top of objects.   Eventually the force on the top is reduced so much that the force of the air on the bottom of the objects is able to overcome the weight and pushes the object up out of the container. When the particle meets the moving air stream the particle is accelerated sideways.  This design is also an example of how drafting works in a chimney to make sure smoke leaves the chimney.

 

A slightly similar design is used in atomizers (fancy perfume sprayers), lawn sprayers for garden hoses and some car washing attachments for garden hoses.  The design and reasoning is slightly different from what is described above. 

All three of these atomizers rely on the larger force of the slow moving air in the container to push down on the surface of the liquid while the faster moving fluid reduces the pressure on the open end of the tube.