A recreation of Norman Tuck’s kinetic museum exhibit. Pluck a string and its sound wave is painted onto a spinning striped drum. When the string’s pitch lines up with the drum’s spin, the wave appears to freeze in mid-air — an illusion built from persistence of vision.
A real string vibrates far too fast for the eye to follow. The drum solves that: as it spins, each fresh stripe lets you glimpse the string for just an instant, at a slightly later point in its vibration. Your eye holds onto each glimpse for a fraction of a second (persistence of vision) and stitches them into a single smooth wave that isn’t really there.
When the string’s frequency is a whole-number multiple of the drum’s spin rate, every revolution catches the string in exactly the same set of positions, so the wave looks frozen. Nudge the speed off that ratio and the snapshots no longer line up, so the wave appears to crawl slowly along the drum. The three strings here are tuned 3:4:5, so they all lock together at the same speeds — try 6, 7.5, 10 or 15 rev/sec.
The original Oscylinderscope is a kinetic sculpture by Norman Tuck, installed in science museums including the Exploratorium.