空気の流れがつくる不思議な現象／A Mysterious Phenomenon Created by the Flow of Air

DENJIRO: Today, I’d like to show you a mysterious phenomenon created by the flow of air. Take a look at this device here. The transparent part is a hollowed out space with a varying width. From the hollowed out space, three thin tubes come out of it. There is colored water at the bottom. The water level is the same in all three tubes. Now, when I let air flow through the hollowed out space, what will happen to the water level in the three tubes? GIRL: Maybe the water level will go down since it gets pushed by the air? DENJIRO: Let’s give it a go. The thinner the width of the hollow space, the higher the water level. Let me explain. When a steady amount of air is flowing, the narrower the width, the faster the speed. In the experiment, the water level was higher when the width was narrower, so we can see that the pressure is lower. That means, the faster the air flow, the lower the pressure. This is known as Bernoulli's principle. Let me show you another experiment using air flow. I have two steel drums sitting on carts. What will happen if I send air in between the drums? GIRL: They’ll get pushed by the air and move away from each other, right? DENJIRO: Now, let’s see what happens. The drums were drawn to each other, and they stuck together. This phenomenon is often explained with Bernoulli's principle. Just like how we saw in the previous experiment, the pressure in between the drums dropped, and therefore they were pulled toward each other. Actually, this explanation is incorrect. So why were the two drums drawn to each other? Let me blow air on the side of the drum. The flow of air gets bent along the curved side. This is called the Coandă effect. Since the drum changed the air flow, the reaction is that the drum gets pulled toward the air flow. NARRATOR: Therefore, the two drums were pulled toward each other as a result of the Coandă effect. DENJIRO: I hope energy will bring you all happiness. Our magic word is "Happy Energy!"