Pendulum Hall
A stone hall, a timber frame, and a brass pendulum about five meters long. Draw it aside, let it go, and watch the Earth turn under it.
A slow swing
The pendulum swings slowly across the hall, there and back about every four and a half seconds. Nothing flashes. Sound plays only if you start with it.
What you can do here
- Draw it aside and let go
- Drag the bob across the hall, or down toward you, and let go. While you pull, a thread holds it to the catch in the box; when you let go, the catch releases it, so the bob starts from rest with no push to the side and swings in a single plane. Foucault started his the same way, by burning the thread.
- Watch the Earth turn under it
- Latitude and Earth set how fast the swing turns. In Paris it turns about 11° an hour, a full circle in about 32 hours, so at Real time you won’t see it move. Set Earth to ten minutes a second and the swing comes round to face you in under a minute. At the equator it doesn’t turn at all.
- Keep it going
- A real pendulum loses a little height on every swing, and so does this one: left alone, its swing halves in about ten minutes. Pull the lever on the box and the drive inside gives it a push on each pass until it is back to a full swing.
- Touch the brass
- Move over the bob and a soft highlight follows your pointer across the brass. Pull the lever and a warm glint catches the bob each time it passes the bottom of its swing.
Use it as your wallpaper
Press F for fullscreen and M to turn the sound off and on; the volume and your sound choice carry over to every wallpaper. The sound keeps playing if you switch to another tab.
Live link
https://whitescreen.tv/interactive-wallpapers/pendulum-hall/#wallpaper- On a computer desktop
- Some wallpaper apps can show a web page behind your desktop icons. Give one the live link above and the scene runs there on its own: no page around it, no ads and no sound.
- On a TV or a spare screen
- Open this page and press F, or use Fullscreen. While it’s in fullscreen we ask the browser to keep the screen from going to sleep.
- On a phone or tablet
- Save image downloads exactly what’s on the screen as a picture. Set it as your wallpaper from your photos; the phone will crop the sides.
A live wallpaper keeps a page running all day. Through the live link the scene draws at most 30 frames a second and stops while the screen is covered, but on a laptop it still costs some battery.
What Foucault showed
In 1851 Léon Foucault hung a 28 kg ball on a 67 m wire from the dome of the Panthéon in Paris. Nothing pushes a free pendulum sideways, so its swing keeps the same direction in space while the floor turns underneath it with the Earth. To the people watching, the swing itself seemed to turn, clockwise, by about 11° an hour. It let anyone see the Earth turning without looking at the sky.
How fast it turns where you are
The swing turns by 15° an hour times the sine of your latitude: once a day at the North or South Pole, about every 30 hours in London, every 38 in Washington, D.C., and not at all on the equator. North of the equator it turns clockwise, seen from above; south of it, counterclockwise.
How long this one is
Judged from the bench and the timber frame, the rod is about 5 meters long, which makes a swing there and back take about 4.5 seconds: the time is 2π times the square root of the length divided by gravity. Foucault’s 67 m pendulum took about 16 seconds. A longer pendulum swings more slowly and keeps going longer between pushes.
About the sounds
Two recordings and one quiet layer: the soft tick of the escapement in the box, the wooden release lever, and the air of a quiet room. The ticks keep their own steady rhythm; they aren’t timed to the swing.
If you’d rather just watch
Picture and sounds generated from our prompts. Motion, controls and mix by WhiteScreen.tv.
