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
Sounds right. Correct me if I'm wrong, but isn't it that the bottom isn't falling as much as it is accelerating upwards at the same rate the top is falling down? Makes it look like the bottom isn't moving.