In previous installments, we brought you video of the amazing levitating Slinky, and Peter Barss wondered how the Slinky had been calibrated to work exactly this way. I asked physicists to come forth, and they have—not just physicists, but an astrophysicist. (Who better to explain levitation?)
Saint Mary's grad Jonathan Dursi, now a senior research associate with the Canadian Centre for Astrophysics, furnished this detailed by elegant explanation:
Sometimes you hear that there's three things taught in first year Engineering (or Physics, or whatever); things fall down; F=Ma; and you can't push on a string.* It's exactly those three things at play...
Yesterday, I posted a slo-mo video of a Slinkeys, which, when dropped while their springs were completely distended, appeared to levitate momentarily, until their springs had time to re-compress, whereupon they began their expected downward trajectory. My pal Peter Barss (who is descended from a real pirate, kids) has a question "for anyone who remembers their physics better than I do."
During most of the its fall, the bottom of the Slinky remains absolutely motionless, which, to my mind, means the gravitational force acting on the slinky pulling it down is exactly balanced by the force compressing the bottom of the...
All the actions is in the first 140 seconds.The remaining four minutes of explanation, involving claims of "information transfer" and "signals," strike me as, frankly, bulltwaddle. Much more plausible is the explanation furnished by Andrew Sullivan's Daily Dish, which in turn came from an even more thorough explanation on Rhett Allain's blog at Wired.com.
What you're seeing:
If a slinky is hung by one end such that its own weight extends it, and that slinky is then released, the lower end of the slinky will not fall or rise, but will remain briefly suspended in air as though levitating.
[T]he best thing is to...