The Science Behind the Simulation
A Brief History of Wind Chimes
Wind chimes have been around for a very long time, about 5,000 years. The earliest ones were found in Southeast Asia around 3000 B.C., made from bones, wood, bamboo, and seashells. People believed they could scare away evil spirits and invite good ones.
In China, wind chimes are called "Feng Ling" and were hung in temples and homes to bring positive energy. In Japan, they're called "Fūrin" and are hung outside during hot summers, where the soft tinkling sound is thought to make you feel cooler and calmer. Today, people all over the world use wind chimes for relaxation and meditation.
Length Is the Note
The tubes hanging on screen are all cut to different lengths, and the length is what sets the note. For the 28 mm aluminium tube used here, the pitch works out at about 169 / L² hertz, where L is the length in metres. Middle C needs a tube 0.80 m long. The C one octave above it needs only 0.57 m.
Because the length is squared, a small change in length is a big change in pitch. Open the settings, change the scale or the number of tubes, and watch the tubes get recut to their new lengths right in front of you.
Why the Cord Goes 22 Percent Down
Grab a ringing tube anywhere along its middle and you choke it. But a hanging tube has two quiet spots where the metal barely moves while the rest of it swings, and the upper one sits 22.42 percent of the way down from the top.
Hang the cord there and you're holding the one part that was not going anywhere, so the note rings on instead of dying in your fingers. Real chimes are drilled at that point, and so is every tube here, which is why the cords meet the tubes a little below their tops rather than at the very end.
Chimes Are Not Harmonics
Pluck a guitar string and its overtones land at 2×, 3× and 4× the main note. Whole numbers, which is a large part of why a string sounds sweet.
A metal tube behaves differently. Its overtones sit at ratios of 1 : 2.76 : 5.40 : 8.93 : 13.34, and none of those are whole numbers, so they never settle into a chord with the fundamental. Those clashing overtones are the metallic clang you hear in the first fraction of a second after a strike. They fade quickly and leave the long pure hum underneath. Every note you hear is built from those five ratios as it is played, not from a recording.
Where You Hit It Changes What You Hear
Hit a tube at its middle and you land right on a quiet spot belonging to the second and fourth overtones. They never speak, and the note comes out pure. Hit it well off-centre and they do speak, and it clangs.
The wooden striker hangs at the vertical middle of the whole set of tubes, so it catches the short tubes near their own middle and the long tubes well above theirs. The short ones sing and the long ones clang, with no extra code asking for that. The chime also sways, so the striker never quite hits the same height twice and the same tube sounds a little different every time it rings.
How the Wind Actually Gets In
Wind pushes on everything, but the part it really works on is the sail, the flat paddle hanging on the long cord underneath. The drag on a flat plate is 0.5 × air density × drag coefficient × area × speed². At 12 mph that comes to roughly 0.15 newtons. The striker and the sail together weigh about 0.66 newtons, so that push swings the pair about 12 degrees off vertical. The sail hangs below the striker on a cord of its own and carries only its own weight, so it swings out to roughly twice that angle.
Double the wind and the force goes up four times over, because the speed is squared. The pair swings past 25 degrees and the sail past 50. That squared term is why a gust throws the chime instead of nudging it.
The striker itself is small and feels only about 5 percent of what the sail feels. It moves because the sail is dragging it sideways on a cord, and when it has been dragged far enough it reaches a tube. The sail always goes first and the striker follows it, which is easy to watch once you know to look for it.
Wind Is Not One Number
A forecast gives you one wind speed, measured 10 metres up. Down where a chime hangs, the ground has been dragging on the air the whole way. At 2 metres you get about 73 percent of the reported speed, and at the height of the grass only about 41 percent. Watch the grass and the chime together during a gust. The grass moves less, and it's supposed to.
Real wind also arrives in lulls and surges. Gusts here are a slow random walk around the average, so quiet stretches and busy stretches happen on their own with nothing scheduling them. The turbulence itself is carried along downwind at the speed of the wind, an idea from the 1930s known as Taylor's frozen turbulence. A gust reaches the scene as a front that crosses it. The streaks far upwind stretch and brighten first, then the grass bends, then the ribbon under the plate snaps straight, then the sail swings out and the chime rings.
The dust and seeds in the air are not a decorative loop. Each speck is pushed by the same wind the sail feels, with its own weight and its own drag, so heavy ones lag behind a gust and light ones go with it. A streak is drawn exactly as long as the distance the air moved in the last 55 milliseconds, and under a certain speed it is not drawn at all. That's why a lull empties the sky and a gust seems to appear out of nothing.
It Is a Real 3D Rig
Everything on screen is measured in metres, kilograms and newtons. The plate, the tubes, the striker and the sail are masses joined by cords that cannot stretch and are free to go slack, which is why you can catch a cord bellying out and then snapping taut a moment later.
The top plate hangs on three short cords rather than one. Hang a disc from a single cord tied at its middle and nothing is holding it level, because the cord pulls through the same point the weight acts through. Real chimes use a three-cord bridle, and so does this one. The whole assembly still swings, and the disc still tilts with the swing, but it never rolls over on its side.
The physics runs at up to 240 steps a second whatever your screen is doing, so a slow phone gets the same collisions as a fast desktop, just drawn less often. Drag the sail or the striker with a mouse or a finger to play the chime by hand, or drag anywhere else to orbit the camera.
Why It Sounds Good (Music Theory)
The default scale is C Major Pentatonic: C, D, E, G, A. "Penta" means five, so this scale has only 5 notes instead of the usual 7 in a regular scale.
Here's the magic: these 5 notes sound good together no matter what order you play them! That's why wind chimes never sound "wrong". There are no clashing notes in a pentatonic scale. Musicians call this a "foolproof" scale because you really can't hit a bad note.
Random timing + pleasant notes = the relaxing ambient sound that makes wind chimes so soothing.