The Coandă effect: how a ping pong ball can float on air


The Coandă Effect is the tendency of a fluid jet to be attracted to a surface. When you put a ping pong ball on over the nozzle of the vacuum cleaner that pushes air through that nozzle, then the ping pong ball will stay put in there. It will float on air due to this Coandă Effect.

What happens there? the air tries to push through the ball and it can’t so it does around it and wants to go i a straight line due to the speed it has. This makes the air closer to the ball to be attracted away from the ball alongside with the rapid stream that just went away from the ball.

Moving air from the ball into the stream makes the air pressure right near to the ball go way down which, in turn, makes the air stream get close to the ball. In this way, the air, instead of flowing away when it meets the ball, it will flow right next to the ball grabbing that ball in its grasp.

Also, even if you tilt the nozzle a couple of degrees the ball will still be there. Interesting phenomenon, eh?

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