Circle and Square 2

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

(Note: The drag in the upward direction is in equilibrium with the gravitational force in the downward direction, and they are omitted in this diagram)

Experimental procedure and explanation:

• First, use the flow from a dryer to levitate the sphere. The point to be noted here is to not move the dryer around.
• Next, try the same thing with a cube. It cannot be made to levitate.
• This experiment proves that the explanation seen in many scientific books, “The pressure is lower where there is a flow from the dryer,” is incorrect.
• The correct explanation is that the air flows along the curved surface with a round object (Coanda effect), while with a square object, the air will flow along the flat surface and then away (separation). The force acting on the object will change depending on the direction of separation.

[Note]	Often, this is explained as "The flow is faster where the dryer air is blowing, and the pressure becomes lower according to Bernoulli's theorem, and the surrounding objects get drawn." This is incorrect. The pressure where dryer air is flowing is about atmospheric pressure (See references for detail).
[Keywords]	Coanda effect, separation, momentum theory
[Related items]	Circle and Square 1, Circle and Square 3
[Reference]	“Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, pp. 214-215 and 206-209 “The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 140-143