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.
This kind of shit is why I love physics.
Is this for real? Any physics fans have more info and can possibly explain this without too much jargon?
Update: More info at blogs.discovermagazine.com
Holy shit this gif
Mmm… The easiest way to explain it without any physics jargon is probably this: When the slinky distended like that, it’s found a state of balance between the tension of the slinky to return to the compressed state and the force of gravity. In this state, the length the slinky has extended will give it a tension of 1G, meaning that the slink is pulling on itself in an equal amount that gravity is pulling on the slinky.
So now think of the slinky again just in terms of what forces are being applied. The top is experiencing a downward pull of G (gravity) + G (tension equal to the pull of gravity. The bottom part is being pulled downward by the same amount of G (gravity), but is being pulled up by the tension of the spring, so -G (meaning it’s being pulled upward with the same level of force that the top is being pulled downward). So when you let the top go, it’s being pulled at G+G, so it gets pulled down. The bottom is being pulled up and down with the same force (G-G) so it just kind of sits there.
Eventually the two ends meet, and (+G+G)+(-G+G) level out to just the whole thing being pulled down with G (the pull of gravity).
Anyway, that’s about as simple as I can make it. The trick is to understand that each end of the slink is experiencing the same pull and direction of gravity, but opposite directions of tension. The whole thing’s being pulled down, but the bottom part is being pulled up at the same time by the tension of the spring.
Easiest way to explain this is that the slinky is a spring and the bottom of it is being pulled up (since the spring is compressing) with the same force as it is being pulled down (by gravity).
This means that the very bottom of the spring is at an equilibrium and won’t begin to accelerate until the spring is fully compressed (no longer pulling the bottom of the slinky upward).