Newton's cradle, except this time you're allowed to mess with it.

Newton's cradle is one of the most quietly elegant physics demonstrations that exists, and also one of the most fidgeted-with desk toys on the planet. Pull one ball back, let it go, and it swings in, stops dead, and somehow the ball on the far end flies out at almost exactly the same speed — while everything in between stays perfectly still. That's momentum and energy conservation happening in a single visible collision, no math required to notice it.

The Cradle preset gives you the classic five-ball row, ready to swing the moment you pull one aside and release it. Because it runs on the sandbox's real physics engine — not a looping animation — you're not stuck with the textbook version. Pull back two balls instead of one. Swap a ball's material to rubber or ice. Nudge the whole thing off-axis. The chain reacts exactly like real balls would, for better or (very entertainingly) worse.

This is where the live readouts panel earns its keep. Watch the momentum number on the struck ball drop to zero at the exact instant the number on the far ball jumps up to match it — total system momentum barely moving the whole time. It's conservation of momentum, not as a rule you're told to accept, but as two numbers trading places in front of you.

And because it's built on the same four-level Knowledge system as every other preset, the "why does it always send out the same number of balls that went in?" question gets answered differently depending on where you're standing — a plain-language answer at Curious, the full elastic-collision math at Expert. Same cradle, same swing, as deep as you want to go.

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