Flying Octopus

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What type of experiment is this?

Experimental procedure and explanation:

• Make an “Octopus balloon” by attaching eight legs made of newspaper to a balloon with a diameter of 22 cm (commonly available size); the same type of balloon is used in “A Balloon that Floats at an Angle (Sequel)”.
• First, blow wind slightly at an angle with a hair dryer, and fly the balloon. The octopus balloon floats even if the dryer is tilted at an angle (the principle is the same as that in “A Balloon that Floats at an Angle (Sequel)”).
• The balloon floats because by attaching the newspaper legs, (1) the whole body becomes heavier and the wobbling decreases, and (2) the center of gravity is lowered because the newspaper is attached underneath and the stability is improved.
• Next, move the octopus balloon directly above the dryer with the dryer pointing straight upward. The legs appear to be moving and the octopus balloon appears to be dancing. At this time, the balloon floats due to air resistance, and the movement of the legs is also attributed to the same. Further, it is observed that the air resistance increases as the legs roll up, which increases the height at which the balloon floats.

[Keywords]	Coandă effect, Momentum theory
[Related items]	A Balloon that Floats at an Angle (Sequel)
[Reference]	“The Wonders of Flow”, Japan Society of Mechanical Engineering, Kodansha Blue Backs, P128-133.

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