"John Larkin" wrote in message
...
On Fri, 20 Aug 2010 06:01:25 -0500, John Fields
wrote:

On Thu, 19 Aug 2010 18:15:25 -0700, John Larkin
wrote:

On Thu, 19 Aug 2010 16:24:26 -0500, John Fields
wrote:

On Thu, 19 Aug 2010 10:49:59 -0700, John Larkin
wrote:

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



"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."
Hey that was on my "quotes of the day" yesterday. :-)
MikeK

A vacuum is a hell of a lot better than some of the stuff that nature
replaces it with.
- Tennessee Williams