A pendulum is deceptively simple: a weight on a string, swinging back and forth under gravity. It's also one of the oldest tools in physics — clock pendulums kept time for centuries off exactly this motion — and it's still one of the clearest ways to see periodic motion happen: the same back-and-forth pattern, repeating on a schedule that barely cares how big the swing is.
The Pendulum preset hangs a bob from a pivot and lets you pull it back to any angle before releasing. Because the sandbox runs an actual physics engine rather than a canned swing animation, you get to test the things a real pendulum does — like the fact that (for smaller swings, at least) a heavier bob swings at almost the same rate as a lighter one, which surprises basically everyone the first time they see it.
Turn on the live readouts and watch the energy numbers trade places on every swing: kinetic energy peaks at the bottom where the bob is moving fastest, potential energy peaks at the top of each swing where it's momentarily still, and the total barely moves the whole time. It's the same energy-conservation story as the rest of the sandbox, just told in a nice, obvious, back-and-forth rhythm instead of a single collision.
Like every preset, the pendulum scales with the sandbox's four Knowledge Levels — "it swings back and forth because gravity pulls it down and it has momentum" at Curious, small-angle approximation and the period formula once you're at University or Expert. Same string, same bob, as much math as you're in the mood for.
Try this
Time the swing. Count how long one full back-and-forth swing takes. Now change the bob's mass — does the timing change?
Change gravity. Try the Moon or Jupiter gravity presets and swing the same pendulum. Watch the period change dramatically.
Watch energy trade places. Turn on kinetic and potential energy readouts and watch them cross over twice per swing — once on the way down, once on the way back up.
Go play with it yourself
No signup, no download — it opens straight into the sandbox with this scene already loaded.
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