“Acoustic dispersion” refers to the phenomenon of a sound wave separating into frequencies as it passes through a material. That may sound like a bunch of fancy terminology, but this video of a man skating over black ice in Stockholm shows just how the science of acoustic dispersion works—and sounds.The video was shot on a lake called Lissma Kvarnsjö, just outside of Sweden’s capital city. It shows a man skating over a long stretch of thin black ice (45 mm thin, according to the uploader, Henrik Trygg) with sounds echoing around him and into the surrounding forest. The sounds are eerie, almost science-fiction-like—as if the aliens in War of the Worlds are singing through the trees. As the man glides along, he seems unbothered by the strange sound his skates are creating; that’s because he can’t actually hear what we hear. According to Neatorama, it takes some distance from the point of impact for the sound to properly reverberate.
There are other icy examples of acoustic dispersion on YouTube if you go looking, like this one from the Andrews Weather Center in North Carolina, which accurately describes the sound as “pew-pew.” NPR furthers that idea in this video, comparing the sounds to the laser blasts in Star Wars. The latter video also gives more examples of how acoustic dispersion works and where you might hear it, like in a glass of ice water or the coils of a moving Slinky.
So if you’re ever walking through the woods and hear what sounds like alien communication or laser sounds, fear not—you’re probably not about to be abducted, but are merely witness to the awesome power of real-world science.
Featured Image: Henrik Trygg/YouTube
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