Explore experiments

A pendulum cannot climb higher than it fell

A six-kilogram bob is pulled aside and let go. It will swing down, sweep along the floor, and rise on the far side — and it will not, ever, come back higher than where it started. Everything it has at the bottom it bought with height on the way down. The block is placed exactly where the bob still has enough left to reach it. Move the rope length, change the bob's mass, and see which of those two the arrival speed actually cares about.