Experiment: I hold the slinky and let it fall freely to the ground
If you keep your eye on the bottom of the Slinky, on the last curl at the very end, you will notice that as the top of the Slinky starts to fall, the bottom doesn’t drop. It just hangs in the air, levitating, as if it had its own magic carpet. It will stay there, hovering quietly, until a wave, or signal, passing through the Slinky finally reaches it. Apparently, the bottom doesn’t know it’s supposed to fall, so it sits there, seeming to defy gravity, until the very end.
-A Slinky is a loose tension spring. If you let the whole thing uncoil and hang down, the tension is enough to hold up the bottom against the pull of gravity.
-Because the Slinky is dropped from the top, Cross explained in his study, it takes time for the motion wave to travel down the spiral and “communicate” to the bottom part that the top part fell — and that the tension is no longer there.