Float a balloon with a stick

Let's take a look!

What type of experiment is this?

Experimental procedure and explanation:

• Attach a plastic stick to a balloon with a diameter of 22 cm (a commercially available size); this is the same as that in “A Balloon that Floats at an Angle (Sequel)”.
• Fly the balloon directly above using a hair dryer. Then, tilt the dryer at an angle and float the balloon at an angle.
• The balloon floats stably when a plastic stick is attached because (1) the whole body becomes heavier and the wobbling decreases, and (2) the center of gravity decreases and the stability becomes better.
• The reason it floats at an angle is that three forces—lift, air resistance (drag), and gravity—attributed to the bending of the flow along the balloon (Coandă effect) are balanced.
• Next, attach a stick to a balloon with a diameter of 45 cm (inflated to about 50 cm) and perform the experiment. Large balloons also float well.

[Caution]	Many books and internet postings attributed the balloon floating at an angle to the “wind from the dryer being faster than the surrounding air, which drops the pressure causing the balloon to be sucked according to Bernoulli's principle.” However, this explanation is incorrect.
[Keywords]	Coandă effect, Momentum theory
[Related items]	A Balloon that Floats at an Angle (Sequel), Bernoulli’s principle
[Reference]	“The Wonders of Flow”, Japan Society of Mechanical Engineering, Kodansha Blue Backs, P128-133. “Illustrated Fluid Dynamics Trivia,” by Ryozo Ishiwata, Natsume Publishing, P206-209.

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