Rotating Two Balloons

Let's take a look!

Three balloons are tied together with a string and floated in the airflow from a circulator.
The balloons move around and collide with each other but do not fall.
When a balloon begins to move out of the airflow, the flow bends around it due to the Coandă effect and is directed outward. At this point, a force acts between the balloon and the airflow, attracting them to each other. The flow experiences an outward force, while the balloon experiences an inward force that pulls it back into the airflow—an example of Newton’s third law (action and reaction). In this way, each balloon remains within the flow.
This video was produced with the support of the JSPS Grant-in-Aid for Scientific Research (18K03956).

[Keywords]	Properties of flow around objects, momentum theory
[Related items]	Lifting a Balloon with Circulator
[References]	Ryozo Ishiwata and Mitsumasa Nemoto, “The Wonder of Flow,” Kodansha Bluebacks, pp. 128–133, pp. 114–117.