Mole Jump

Let's take a look!

Watch the video on YouTube.

What type of experiment is this?

Experimental procedure and explanation:

• A blower was used to try to cause a mole (made of styrofoam) to float upward when subjected to blowing air. This experiment was used as a hands-on exhibit of the “Mysteries of Airflow” by the Japan Society of Mechanical Engineers.
• The first mole has a rounded head, and when the blowing air is aimed at the mole’s head, the mole floats upward. When a jet flow (flow that gushes from a nozzle or hole) is applied to a rounded object, a property (called the Coanda effect) is exhibited in which the flow easily bends along the rounded object. In this case, the flow bends downward, and a downward force is received from the mole. An upward force then acts on the mole through this counteraction, and the mole floats upward.
• The second mole is angled at both the top and the bottom. Moreover, when the blowing air is directed at the bottom of this mole, the air flow bends downward and a downward force is received from the mole. Conversely, the mole receives an upward force from the flow because of counteraction and floats upward.
• Numerous scientific books and such material explain that “because the flow rate is higher at the location where the wind is blowing than at the location where the air is stationary, the pressure is smaller based on Bernoulli’s principle.” However, this concept does not correctly explain why the round-headed mole floated upward. However, if the concept is correct, when the head of the second mole was blown with air, the mole should have floated upward, which did not happen.
• However, with the round-headed mole, the air flows along the round surface (Coanda effect), and with the slanted flat surface, the air flows outward (separation) along the surface. Thus, the force acting on an object changes depending on the direction of outward flow.
• The third mole with the square shape did not move upward smoothly, i.e., a state of flow like that of the other two moles was not achieved.

[Attention]	is often explained that “because the flow rate is higher at portions where the wind is blowing than at portions where the air is stationary, the pressure becomes lower based on Bernoulli’s principle, and surrounding objects are drawn toward the object.” However, this explanation is incorrect. The pressure of the location where the wind is blowing is nearly equivalent to the atmospheric pressure. (For details, please refer to the bibliography.)
[Keywords]	Coanda effect, separation, momentum theory
[Related items]	Circle and Square 1, Circle and Square 2, Circle and Square 3
[Reference]	Ryozo Ishiwata, “Illustrated Fluid Dynamics Trivia (Zukai Zatsugaku Ryutai Rikigaku),” Natsume Co., Ltd., pp. 214-215 and pp. 206-209, pp. 224. The Japan Society of Mechanical Engineers, “The Wonders of Flow (Nagare no Fushigi),” Kodansha Blue Backs, pp. 140-143. The Japan Society of Mechanical Engineers, “The Wonders of Flow Exhibit” http://www.jsme-fed.org/contests/fushigi.html