No matter how long the slinky is, the bottom of the slinky will stay still (hover) until the top reaches it. Even if the slinky is over 1000 feet long.
OH OH OH OH OH OK SIT DOWN FRIENDS I AM GOING TO EXPLAIN THE THING TO YOU
When you drop a slinky the first thing that happens is that the top “swirl” of metal you were holding is released and drops to hit the swirl below it. This then pushes the swirl below it down and so on and so on until finally the slinky drops.
The bottom doesn’t drop when you release the top because the information that the slinky has been dropped hasn’t reached it yet.
This is in accordance with Newton’s 1st Law: that a thing with continue to do it’s thing in exact the same way unless another thing tells it to do something different.
In this case it applies when the man lets go of the slinky. He has created an external unbalanced force (where one pull is stronger than the other: in this case gravity is the stronger) which causes the top swirl to change it’s state of motion i.e. the top slinky swirl moves down. This acts upon the swirl below it, which in turn acts on the swirl below it and so on.
However, the force on the bottom of the slinky is still balanced, as it inhasn’t been acted on by an unbalanced force (yet). THEREFORE it continues to do exactly what it’s been doing, not moving.
This may seem crazy, but it happens in loads of other places too. For example: the reason cars squish so much when they crash head on is because though the front of the car has been stopped by the wall, pole. other car or unfortunate pedestrian, the back of the car continues to move at the same speed until it also encounters said barrier.
(Also because cars are designed with crumple zones but let’s not get into that.)
So yes friends, that was the slinky trick explained.
it’s because the upper bit of the slinky is pulling up the bottom bit whilst falling. you’re welcome.