Let's take a look!
What type of experiment is this?
Experimental procedure and explanation:
- Make a ring from polystyrene foam board (2 mm thick, sold at home improvement stores, etc.) and attach a small balloon around it. If you don’t have a polystyrene foam board, you can use thick paper that is not too heavy.
- If you blow it from below with a dryer, it will spin around.
- The spinning in the air is due to the two functions of the flow.
- ① The flow bends along the balloon, causing a force to be exerted on the flow downward (lower right downward shown in the explanatory figure), and as a reaction, the force acts upward on the balloon. This force acts to buoy the whole structure. This is the same principle as "A Balloon that Floats at an Angle".
- ② The flow hitting the balloon also generates a force called air resistance. This air resistance is the force that rotates the whole structure.
|[Keywords]||Coandă effect, air resistance|
|[Related items]||A Balloon that Floats at an Angle|
“The Wonders of Flow,” Japan Society of Mechanical Engineering, Kodansha Blue Backs, P128-133