Sci/Tech A striking phenomenon: "Levitating" Slinky trigger physicists to explore. (video)

[tom_mai78101]

Spurred by a wave of recent Web videos showing the bottom of a dropped Slinky hovering dramatically in midair , physicists have provided new insights into this phenomenon, from the existence of shock waves in the falling Slinky, to a remarkably universal "levitation" time for a Slinky on other planets or moons despite their different gravitational fields.

In February 2000, the late science writer Martin Gardner posed a simple question intended for physics students, but also triggering a new round of papers and videos on the much-studied toy. Gardner wrote: "If you hold one end of a Slinky, letting it hang down and then drop it, what happens?"

"It turns out the bottom stays suspended, levitating in air for some period in time," said Shimon Kolkowitz, a physics graduate student at Harvard University in Cambridge, Mass. As an undergraduate at Stanford University in Palo Alto, Calif. in 2007, Kolkowitz wrote a paper now posted online for a class taught by his professor, physics Nobel Laureate Robert Laughlin.

And recently, Bill Unruh, a physics professor at the University of British Columbia, in Vancouver, heard some colleagues in the faculty lounge discussing a video of the levitating Slinky. As a result, Unruh, a world expert in black hole radiation, became captivated with Slinky physics.

Read more here, and video!

 

[The Helper]

Nice read on the whole article. Interesting stuff!

 

[Dan]

I've never thought about it before. The tension disintegrates as it collapses at the top; however, the bottom doesn't adjust to that tension change until it literally reaches zero.

What I want to see now, is a really, really, really, really, really long slinky drop where we can witness this without slow motion and record how long it may be delayed.

 

[DarkRevenant]

Without reading the article, the reason for this seems obvious to me. The slinky is one long elastic object, each section pulling on the other one with as much force to exactly counteract gravity. Dropping it at the top takes time to travel down to the bottom (elastic object), but until then, each section of slinky still is being pulled up with enough force to equal gravity. The reason it will suspend there for a long time (suppose you had a slinky a mile high, the bottom really would more-or-less suspend there for the entire drop) is that each section of the system is individually in equilibrium with gravity and won't register a change until the section above it changes its force on the one below it. Since the equilibrium is with gravity, the shockwave travels at the same acceleration as gravity, meaning that the bottom will just stay there.