PURPOSE: To illustrate the Coanda effect in a dramatic way.

DESCRIPTION: A large styrofoam ball is contained in an inverted funnel which is connected to an air blower. When the blower is turned on, the ball rises to the top (narrow end) of the funnel. The air follows the surface of the ball as it passes the ball's surface. The reaction force on the ball pushes it up into the funnel.

This demonstration is often said to be a result of the Bernoulli effect; this explanation is INCORRECT!

The correct explanation involves the Coanda effect. When the air stream flows past the ball, some of the air follows the contour of the ball and only leaves after it moves a significant distance along the surface of the ball, as illustrated in the drawing below. In effect, the ball is "pulling" the air around its surface. There must always be some reaction force on the ball, which points in the direction of the air stream and upward, holding the ball in the air. Click your mouse on the drawing to see the web page from which it was taken.

The Coanda effect is also responsible for such phenomena as the pulling of the convex side of a spoon into the water stream from a faucet, as seen in Question of the Week #228.

SUGGESTIONS:

REFERENCES: (PIRA 2C20.35) A smaller version is available: F5-05: SMALL BALL AND FUNNEL - COANDA EFFECT

EQUIPMENT: Pre-assembled setup as photographed.

SETUP TIME: None.