Mersa wrote on Jul 9
th, 2020 at 7:19pm:
Noooooooooooooo put this thread back in the archive
No! Don't do that yet.
I missed most of this at the time, and I feel the arguments that were being made were along the right track.
A very long time ago there was a paper by "George Alsation" accessible. I can't seem to locate a non-Forum home page, which existed at one time. That contained a number of little examples trying to get to grips with the mechanics of the sling, and Apo's diagrams seem to have been illustrating one of Alsation's points.
It looks to me like the dialog between him and JudoP broke down over the description of forces and (probably) some language matters.
The nub of all this is that to increase the speed (kinetic energy) of the sling stone you have to do work on the 'hand' end - what would be the support point if this were a 'high school physics' simple pendulum.
For that you need to move the support point (the hand) , and you also need the pendulum bob to be traveling in a curve in order to tension the cord. If you move the support point appropriately you couple energy into the slingstone and hence increase its speed.
On Apo's diagrams, he was dealing with the motion of the slingstone from W (west) via S and then finally to E, or thereabouts. Throughout this region the sling is pulling against the hand such that movement of the hand towards the north (as Apo was describing) will do mechanical work on the system, increasing the sling stone speed.
Apo also touched, as far as I can make out, on the view of the sling as like a simple pendulum where instead of just a constant gravitational acceleration there is instead a variable acceleration which is due to the movement of the support point. This view is confirmed if you grind through to the Lagrange equation of motion.
I have to admit I wondered whether Apo was actually "George Alsatian", so similar was the basis of his arguments, but who knows?
Apex-apoc = Apo