Slinky Drop Answer
Why Physics Stack Exchange recommends it
Physics Stack Exchange users link it as the standard demonstration that the bottom of a released slinky does not start falling until a compression wave arrives, whenever questions touch on how fast forces and signals propagate through a body.
Recommended by 3 people across 3 different months, 2012 to 2025.
What it is
A short Veritasium video showing, in 300 fps slow motion, what happens when a slinky hanging under its own weight is released. The bottom end stays in place until the collapsing top reaches it. It is the answer clip to Derek Muller's earlier slinky drop question.
What people said
Recommends Mark Eichenlaub · 2012-10 · Physics Stack Exchange · on “Wave pulse on a freely falling rope”
@AkarshSimha The rope doesn't support compression very well, and I'm not sure that the speed of sound is what's important here. See this video for the example of a slinky. [this video]
Recommends joshphysics · 2013-03 · Physics Stack Exchange · on “Slinky base does not immediately fall due to gravity”
What an awesome question! By the way, as far as I know, the original video is here [this video] for those interested. One key to understanding this is the following fact from classical mechanics that is a version of Newton's second law for systems of particles: The net external force acting on a system of particles equals the total mass $M$ of the system times the acceleration of its center of mass $$ \mathbf F_{\mathrm{ext},\mathrm{net}} = M\mathbf a_\mathrm{cm} $$ In the case of the slinky, which we can model as a system of many particles, the net external force on the system is simply the weight of the slinky. This is just given by its mass multiplied by $\mathbf g$, the acceleration due to gr
Recommends Dale · 2020-08 · Physics Stack Exchange · on “Is the effect of friction force transferred INSTANTLY in this case?”
Does it mean that the effect is transferred INSTANTLY and if not can we calculate the delay ?? Well, there is more than one effect, and different effects happen at different times. First, instantly when you release the friction on the rope the center of mass of the system consisting of the rope + the bob begins to travel tangentially. Second, the tension in the part of the rope immediately adjacent to your hand begins to relax. This relaxation of the tension propagates as a longitudinal wave through the material of the rope. The speed of propagation of this wave is the speed of sound in the material of the rope. Third, the bob will continue to move in the circular path until that mechanical
Cites Tyler V. · 2014-03 · Physics Stack Exchange · on “Speed of Sound/Push in Supersonic Flight”
I've learned from things like the Veritasium Slink Drop [this video] and the old "break the speed of light by pushing on the end of a very long pole" thought experiment that objects have a "speed of push" which is commonly referred to as the speed of sound. My understanding of this being that information about movement can't propagate through a medium faster than the speed of sound in that medium. So my question is: What happens to air when a supersonic jet flies through it? On the one hand it would seem that air can't move out of the way of the jet faster than the speed of sound in the air, however the jet obviously displaces the air at supersonic speeds anyway. So what's happening?
Cites lminsl · 2018-03 · Physics Stack Exchange · on “Experiments with slinky”
Can someone explain this results? [this video] If I grab one of the ends of the slinky, then the slinky will extend because of the gravity. Assume that the other end of the slinky does not touch the ground, and when we let go the slinky, (with inital speed $0$), I saw that the other end of the slinky does not move until the upper part comes really close.
Cites Jagerber48 · 2024-01 · Physics Stack Exchange · on “Dropping a skyscraper (hypothetical question)”
The question asks about a skyscraper but the comments clarify that answers can replace the skyscraper with any (colloquially) rigid object. Skyscrapers are made of many materials held together in many ways. I’ll consider a simple long steel I-beam. No material is perfectly rigid. If it were then You could send signals faster than the speed of light by pushing on one end and instantaneously receiving the motion at the other end, no matter how long the material. Real materials consist of atoms/molecules held together by electronic bonds. They can be modeled as masses connected by springs. In other words, all materials are like big slinky’s. Stiff materials like metals have very high spring con
Cites BioPhysicist · 2024-01 · Physics Stack Exchange · on “A mass is hanging by a thread from another mass, which starts to fall. What happens and why?”
In the case of dropping a slinky, it is option 2 [this video] . For the masses on the string, a good approximation is option 1 if the mass of the string is negligible, but it does take some time for the "signal" that the blue string was cut to propagate through the black string, so there will be a delay in the time from when the string is cut to when mass B moves. The delay won't be long enough for ball A to collide with ball B though unless the string is sufficiently short.
Cites Dale · 2025-07 · Physics Stack Exchange · on “Why the upper section falls faster than the bottom section when the line is cut?”
@BrendanMitchell is correct, the book is wrong. At the moment that the string is cut the center of mass falls at g. The top falls faster than g, but the bottom falls at less than g. In fact, with a slinky you can visibly see that the bottom stays in place until the compression wave arrives. So at first it “falls” at 0 g. [this video]