A Balloon that Floats at an Angle (Sequel)

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What type of experiment is this?

Experimental procedure and explanation:

• In “A Balloon that Floats at an Angle” published in December 2009, we conducted an experiment to float a balloon obliquely upward using a dryer. In that experiment, the balloon had a diameter of 45 cm. In this experiment, the balloon diameter is 22 cm (commonly available size).
• A nozzle made from a plastic bottle is attached to the tip of a dryer. The nozzle is used to speed up the flow and narrow the jet (flow ejected from nozzle and hole) to easily create a Coandă effect (described later). The Coandă effect occurs in the case of a jet; a thinner jet allows the flow to be less widespread and thus be more effective.
• First, the balloon is blown straight up with the dryer. The balloon floats because of air resistance (drag) received from the wind from the dryer.
• Next, if you tilt the dryer obliquely in a gradual manner, the balloon will fall because it is too light to work.
• Therefore, we experiment by attaching a long and thin strip of newspaper to the balloon. This restricts the balloon from shaking too much, and therefore, even if the dryer is tilted, the balloon floats stably.
• This is attributed to attaching the newspaper tail: (1) the whole body becomes heavier and the wobbling decreases, and (2) the center of gravity is lowered further by the newspaper and the stability is improved. If you repeat the experiment with a light balloon, it can be floated at an angle. However, if it is too long, it will become heavy and will not rise high; if it is too short, it will sway and become unstable. Therefore, please adjust the length.
• The reason the balloon floats at an angle is like the explanation provided in “A Balloon that Floats at an Angle”. The flow of air is bent along the balloon (Coandă effect), and a force acts on the air in the direction perpendicular to the flow. This reaction becomes a force called “lift.” Then, the air resistance also acts, and the resultant force of these two forces balances itself with gravity.

[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 and based on a misunderstanding of Bernoulli’s principle as being “where the flow is fast, the pressure is low.” Bernoulli's principle is the law of conservation of energy, which states that “if there is no energy loss and supply on one streamline, the sum of energy is equal at two points, upstream and downstream.” This cannot be established unless two conditions—a comparison of the two points, upstream and downstream, and zero energy loss and supply—are satisfied.
[Keywords]	Coandă effect, Momentum theory
[Related items]	A Balloon that Floats at an Angle, Supporting a Ball with a Stick, 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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