Sine wave water illusion is incredibly cool, easily explainable

The first thing every kid does with a hose when they pick it up is the same. You put your thumb on the spout and bend the stream to your will. If you grow up and take that one step further, you could come up with something pretty fantastic.

Optical illusions come in all shapes and sizes. Typically, when you think of optical illusions, most people think of perspective based image manipulation. It’s not often that a constantly moving object generates such an illusion. It turns out, this has a lot to do with how fast things move. If you catch them at the right frame rate, constantly moving objects can deliver similar optical illusions. This video is an example if such an illusion, capturing flowing water as it the spout it is pouring from is subjected to specific vibrations and then captured at 24 fps.

In this video, the vibrations from the speaker cause the tube to vibrate in a very specific pattern. This, in turn, causes the water to leave the tube in that same pattern. The different patterns captured here are a result of the tube vibrating at 23hz, 24hz, and 25hz while being captured on camera at 24fps. If you were to conduct this experiment yourself and you were just looking at the water with your eyes, you wouldn’t see the sine wave patterns that are captured by the camera. Our eyes capture the world at significantly faster than 24fps, so the camera serves as an interrupt that allows us to observe this optical illusion.

Experiments like this also help to explain why recent films that have been released at 48 fps are considered so jarring. When we go to the theater, we are used to the 24FPS experience, and movie makers have had a long time to create illusions that look as good as they do in that format. In seeing the world faster the 24fps, we’re losing some of the artificial scale created by that visual experience.