I watched closely, again, and listened, again, to what this professor tried to explain. (Forgive me last time I just tried to explain in plain English why it appears the bottom of the slinky doesn’t move and didn’t study this video closely) The “signal delay” to get from the top of the slinky to the bottom part of the slinky is nonsense. He is attempting to assign some magical property to a slinky. He conveniently ignored what happened when you held the top of the slinky at a fixed height and allowed the slinky to extend under the force of gravity. All you see in this video is the end result of the stretched out slinky dropped from the top after extension so it only appears the bottom doesn’t move.
The easiest I can explain it is every coil on the slinky has fallen as much as it possibly can with spring tension exactly matching gravity. The coiling and twisting properties he tries to explain as “signal delay” is silly. All those “signals” are contained in the tension / torsion of the spring and are stored in all the various kinetic fashions when the spring (slinky) was stretched out. This “storage effect can be seen by the top coils being a greater distance then the bottom coils. Each of those coils are storing energy. If you were to watch the drop that stretched out the slinky in slow motion (which was not provided) you will see the twists and turns as they occured.
P.S. I design aircraft flight control systems. You can spend a lifetime on spring mechanics and still not understand the physics involved. I suspect this professor is demonstrating a case of “protect the hypothesis and protect the model” as is so common as demonstrated in global warming models. He is a lot smarter than me indeed but when he fails to show and explain what happened to that slinky when he uncoiled it (dropped it but held on to the top) I am very suspect of his explanation. In fact, I comfortably call his conclusions bogus. When he and the presesnter start talking about a lead slinky acting differently and whatnot he is engaging in nonsense. A spring is a spring is a spring and they are all subject to the same physics. The exact same thing will happen with a lead slinky, a plastic slinky, or an Obama unicorn fart slinky.
This is nothing more mysterious than a stretched out compression spring and gravity going on. No magic, no delayed signal, no “gravity is faster than light,” no changing center of mass. It is simple spring mechanics and I don’t dare go to the math equations involved.
>Reference for anyone wishing to mathematically challenge me -— Machinery Handbook 26 Edition, pg 285-332
>Hooke’s Law
>engineersedge(dot)com
>K factor
>http://www.newton.dep.anl.gov/askasci/eng99/eng99245.htm
Hmmm...
I worked with a guy years ago who was taking simultaneous measurements of voltage and current and given more time I think he was going to re-discover Ohm's Law. He was very fascinated by the proportionality which he had discovered.
I think this researcher has chosen poor words to describe what I think is happening.
Looking at the video there does appear to be a transition in the behavior of the spring when the coils close completely. The transition between the region where the coils are completely closed, and the region where they are not, does seem to travel downward along the length of the spring.
When this transition finally reaches the bottom of the spring, the spring force accelerating the bottom of the spring toward the center-of-gravity of the spring disappears. The bottom of the spring doesn't begin dropping because it receives a signal, it drops because it lacks the force which has held it in place.
Aside from some torsional effects, it does appear that the region of the spring below the collapsed part, is stationary.
I'm still struggling to imagine how such a non-uniformly extended spring would behave without a gravitational field.