# The Levitating Slinky

Submitted by: FoolsPrussia 5 years ago in
105

When you drop a slinky, the bottom doesn"t move until the top reaches it. Science!
105
There are 22 comments:
Male 462
What happens if you drop one in a vaccuum?

Gravity is what causes the slinky to collapse, not air friction, in a vacuum the lack of air resistance would mean the slinky would contract faster.
Male 39,603

Did anyone else notice, in the first bit where he`s standing holding the slinky, you can totally see his junk in those tight pants.

Looks like he had a good size slinky.
Male 5,811
It`s called elastic force, which in this case is stronger than the force of gravity. Like Altaru said, basic physics. Now if you want to see a really cool application of physics, specifically angular momentum, watch this.
Male 417
That`s awesome ... in the most simple terms, the bottom is being pulled *UP* by the spring at the same rate the slinky is falling as a whole, thus making the bottom remain in the same place.
Male 273
i want to make babies with science <3
Male 3,482
Pretty basic physics at work here, honestly...

Still cool to watch though.
Male 15,832
[quote]What happens if you drop one in a vaccuum?[/quote]
Pretty much the same thing. Air resistance is not a significant factor here. What does complicate the situation is rotation. When you stretch out a Slinky, it also "unscrews," and it tightens back up as the top collapses. That`s why you see the bottom turning as the top falls towards it (~5:00).
Male 3,631
Nah miasmaat, I`m confident that corkscrewing is a product of the spiral structure. However, in reference to your question about what would happen in a vacuum (i.e., in absence of gravity), I think your description of potential energy existing at both ends and collapsing toward the center illustrates the result - it`s gravity that`s keeping the potential energy at the `bottom,` as demonstrated in this video, from resolving in the same manner as the top.

Thus, my hypothesis would be that in a gravity ambivalent vacuum, not only would both ends resolve toward the center BUT do so at a rate that is lesser (top) and greater (bottom) in proportion to their respective speeds under the influence of gravity - adjusted, of course, for lack of wind resistance.
Male 9,524
This is the coolest thing I have ever seen on I-A-B, in my opinion.
Male 3,310
If I had missed some physics classes on spring action this would entertain me. Damn you, education!
Female 298
What happens if you drop one in a vaccuum?
Female 298
I would agree along the same lines as some other people have suggested. My naive explanation:
In an extended slinky there is a pull exerted on both ends toward the centre which is caused by the actual bonds in the atoms in a sense - since the material is ordered in a very ordered framework on an atomic level and extending it maybe puts pressure on these bonds.. widens them and accumulates potential energy which is due to electromagnetic attraction in a sense. This potential energy will increase in a curve and be greatest at the ends. But this `pull` is dependent on the degree of `order` and `tightness` in the atomic framework and in heavy, loose slinkies can be quite low. The attraction of gravity however is assumed to be a constant. When this pull exceeds the potential energy accumulated in the very end of the material of the extended slinky, movement toward the centre is reduced/enhanced. The corkscrewing is simply due to a spiral compressing rapidly against air resistance.
Male 3,631
Likewise, I didn`t realize how rare they`ve become until now. And I enjoyed your thorough evaluation of xiquirpat`s post, which I actually didn`t see before writing my 2nd paragraph which goes toward the same point, but I guess this simply goes to show a peer consensus among the highly scientific minds here at I-A-B, am I right?

Anyway, I was thinking perhaps a better way to describe what I was originally calling "centrifugal inertia" might simply be the potential energy of the spring`s tension? What do you think?

Btw, I`m watching an episode of Star Trek right now, lol. Brb.
Female 2,602
[quote]I don`t know MacGuffin - I`m not a physicist, but my first thought regarding how this action is achieved had to do with what we could discuss in layman`s terms as the falling part of the spiral (the top) almost `pulling` the bottom part up at a constant rate. I think the physicist touched upon this when he mentioned the `twisting motion` of the bottom that was evident in the video. There`s a certain centrifugal inertia that`s present in the extended slinky, so it would actually take MORE work to push the bottom part down at the same rate that the top part is falling - this would prevent the slinky from collapsing until it hit the ground.

I would say that the centrifugal inertia, as I`ve chosen to describe it, simply overrides gravity, as it is a stronger force in that it`s working at a faster rate.[/quote]

Well described, and a good post this one - I like the threads that make you think!
Female 2,602
[quote]The tension in the spring probably overwhelms the force of gravity. But I don`t really know.[/quote]

I think you`re probably right. And as for my comment that "I still don`t get how the bottom of the slinky`s mass stays at exactly the same height ... even in the case of two different slinkies that are made of different materials and have different strengths of spring", thinking about it some more the plastic slinky with the weaker spring extended far more under gravity before release than the metal one did (that`s why they had to release the weaker spring from higher up on a building whereas they could release the other one whilst standing on the ground). So, it looks like gravity extends the slinky by a set amount relative to the strength of its spring as the initial condition, then the spring equally and oppositely counteracts gravity when released owing to that slinky-specific amount of initial extension. Whew!
Male 3,631
I don`t know MacGuffin - I`m not a physicist, but my first thought regarding how this action is achieved had to do with what we could discuss in layman`s terms as the falling part of the spiral (the top) almost `pulling` the bottom part up at a constant rate. I think the physicist touched upon this when he mentioned the `twisting motion` of the bottom that was evident in the video. There`s a certain centrifugal inertia that`s present in the extended slinky, so it would actually take MORE work to push the bottom part down at the same rate that the top part is falling - this would prevent the slinky from collapsing until it hit the ground.

I would say that the centrifugal inertia, as I`ve chosen to describe it, simply overrides gravity, as it is a stronger force in that it`s working at a faster rate.
Male 5,314
i saw all i needed to see in the first 15 seconds
Male 2,422
@MacGuffin

The tension in the spring probably overwhelms the force of gravity. But I don`t really know.
Female 2,602
This page has some useful information about the phenomenon. The animated GIF on it showing a comparison between a slinky and a falling golf ball is pretty informative: the top of the slinky is accelerating towards the ground faster than gravity would otherwise cause a weight to fall. I still don`t get how the bottom of the slinky`s mass stays at exactly the same height relative to its start point until the top catches up, though, even in the case of two different slinkies that are made of different materials and have different strengths of spring (presumably two springs of differing strengths can`t both just be happening to exactly counteract gravity?).
Female 2,602
Fascinating. Intuition might tell you that gravity would both act on both ends at the same time, and it should contract under the effect of the spring as the whole mass falls.
Male 598
just like babies!
Male 3,445
Link: The Levitating Slinky [Rate Link] - When you drop a slinky, the bottom doesn`t move until the top reaches it. Science!