Circle and Square 1

Let's take a look!

Watch the video on YouTube.

What kind of experiment is this?

Experimental procedure and explanation:

• Place a paper carton (rectangular box) and a round can (cylinder) on top of narrow stands.
• Blow air on them through a straw to push them off the stands.
• First, we blow air on the right side of the rectangular box. The box falls to the left side.
• Next, we blow air on the right side of the cylinder. The cylinder falls to the right side.
• The difference between the two is the direction in which the flow is deflected.
• With a rectangular box, the flow is deflected to the right, causing separation at the back of the box. The box receives a force to the left (in the direction opposite to the side the air is blown from), as a reaction to the force acting on the fluid (the right side).
• With a cylinder, the flow is deflected to the left (Coanda effect), and the force to the right is acting on the cylinder as a reaction to the force acting on the fluid (left).

[Keywords]	separation, Coanda effect, momentum theory
[Related items]	Circle and Square 2, Circle and Square 3
[Reference]	“The Wonders of Flow,” Japan Society of Mechanical Engineering, Koudansha Blue Backs, pp. 140-143