{"id":64923,"date":"2026-06-29T04:32:39","date_gmt":"2026-06-28T19:32:39","guid":{"rendered":"https:\/\/phys-edu.net\/wp\/?p=64923"},"modified":"2026-06-29T04:36:20","modified_gmt":"2026-06-28T19:36:20","slug":"the-mysterious-device-that-makes-styrofoam-float-in-midair-visualizing-sound-waves-with-a-kundts-tube","status":"publish","type":"post","link":"https:\/\/phys-edu.net\/wp\/?p=64923&lang=en","title":{"rendered":"The Mysterious Device That Makes Styrofoam Float in Midair \u2014 Visualizing Sound Waves with a Kundt’s Tube"},"content":{"rendered":"

Here is the translated version:<\/p>\n

I’m Ken Kuwako, a science trainer. Every day is an experiment.<\/span><\/p>\n

Think sound is invisible? As it turns out, under the right conditions, sound waves can reveal themselves right before your eyes. On a recent visit to the Tsukuba Expo Center, I came across a device that does exactly that \u2014 tiny polystyrene beads floating up inside a tube, tracing the invisible shape of sound. No textbook needed. You just see it, feel it, and suddenly understand: sound is vibration.<\/p>\n

What is a “standing wave,” and why does it appear inside a tube?<\/h3>\n

The device I encountered is called a Kundt’s tube \u2014 a closed tube at both ends. When sound is fed into it at just the right frequency, something remarkable happens: a standing wave forms inside.<\/p>\n

\"\"
\nA standing wave is what you get when a wave bounces back and forth inside a confined space and interferes with itself. Certain spots vibrate intensely \u2014 these are called antinodes \u2014 while other spots stay perfectly still, called nodes. Think of a jump rope swinging in a big arc and appearing almost frozen in place. That’s the idea.
\nNow, if you fill the tube with fine polystyrene beads beforehand, something magical happens: at the antinodes, where the air is vibrating wildly, the beads lift up and dance. At the nodes, they sit completely still. The result? The wave’s shape becomes visible. You can watch it in action in this video:<\/p>\n