>
>>>>
>>>>
>>>>You don't believe I guessed 100 us? I posted it in SED days before you
>>>>did the tests. You replied "noted", obviously expecting me to be
>>>>wrong. Sorry to disappoint.
>>>
>>>---
>>>Wow, with a chip that big on your shoulder, I'd be willing to bet
>>>you're well on your way to scoliosis.
>>>
>>>Ermm...
>>>Of course I believe you posted it. I acknowledged it, didn't I?
>>>
>>>The only thing I'm disappointed in is that you won't reveal the
>>>reasoning that led up to the guess, so who's to know if it really
>>>_was_ a guess?
>>>
>>>You always say: "Show your work", but when it comes time for you to
>>>walk the walk, you balk.
>>
>>I can't show my work because there wasn't any work, or at least any
>>conscious work. I visualized the impact and guessed. That's what a
>>guess is, a guess.
>>
>>The trick is to guess right. The real trick it to usually guess right.
>>
>>>
>>>Makes one suspect any number of nasty things...
>>
>>Naturally. You need to believe that I cheated somehow. The alternative
>>is intolerable.
>
>---
>Not intolerable, let's just say "unlikely".
>
>However, it doesn't really matter; you came close to the right answer,
>however you did it, and that's that.
>
>Congratulations.
>---
>
>>>Anyway, here're some facts for you; let's see if you can juggle them
>>>around and get 100µs from make to break in the 3 ball case.
>>>
>>>The balls are made from ASTM B134 Grade 260 brass, (70Sn 30Zn) are Mc
>>>Master Carr P/N 9617K47, have a diameter of 0.75" +/- 0.001, and weigh
>>>about 32 grams.
>>>
>>>The length of the suspension is 4.5" from the upper restraint to the
>>>center of the ball.
>>>
>>>The velocity of sound in 70/30 brass is:
>>>
>>>Plane Longitudinal: 4700 m/s
>>>Plane Transverse (shear): 2100 m/s
>>>
>>>The plane longitudinal is for the bulk material, so is probably more
>>>accurate for a spherical structure.
>>>
>>>For a pendulum, the velocity of the bob at the bottom of its arc is:
>>>
>>> V = sqrt {2gL[1-cos(a)]}
>>>
>>>Where V is the velocity in m/s
>>> g is the acceleration of gravity in m/s²
>>> L is the the length of the suspension (the "rod") in meters, and
>>> a is angle from plumb at which the ball is released.
>>>
>>>Wanna play?
>>
>>I already estimated the time, before you even measured it.
>
>---
>Actually, "guessed" is a better word.
I've said "guessed" all along. But what's the official difference between the words?
---
>
>>It's your move next.
>
>---
>I don't think so. You must have missed the earlier:
>
>"Anyway, here're some facts for you; let's see if you can juggle them
>around and get 100µs from make to break in the 3 ball case."
>---
>
>>Do the math and see how close it comes to the measurements.
>>Of course, you already know my guess *and* the experimental results.
>>
>>Sure, do the math and post it.
>
>---
>I've already done the math and found the 150 µs incongruous.
Yikes. My 10-second guess is better than doing the math. A lot less work, too.
>The invitation was extended to you in order to see whether you'd
>independently arrive at the same conclusions I did and, possibly,
>either explain the incongruity or guess at the reason for it, so I'll
>not post my work, yet.
>
>The ball's in your court, so you can either hit it back or walk away.
>
>As for me, this has gotten beyond tedious so I'm ready to quit any
>time.
Hey, it's you project, all that woodwork and wiring and stuff. It's not something I'd care to spend a lot of time on.
When the balls hit, there's a small initial contact area that squishes down and becomes bigger with time, until the relative motion stops and reverses. During that time, a complex shock wave progressively forms as the contact footprint changes; it moves through the sphere, and eventually arrives at the other side and does sort of the reverse action on the next ball. That's absurdly complex, not something I'd attack voluntarily.
When NASA built the S1B moon rocket booster, it was heavily instrumented, perhaps more than any big structure like that had ever been. They didn't realize until after a launch that F=MA is a simplification for a big tall compressible structure. When the rocket engine makes a shot of thrust, the structure compresses but doesn't move much, until the shock wave travels from bottom to top and back. It's very much like driving an open-circuited transmission line with a current source... it's a low impedance until the leading edge makes the round trip.
You could crudely model the rocket or the three ball system in Spice maybe, using transmission lines and diodes and such. As a local redneck geezer likes to say, that's an exercize for the students.
John