On Thu, 11 Sep 2008 07:05:15 -0400, with neither quill nor qualm, Pete
Keillor quickly quoth:

On Wed, 10 Sep 2008 19:01:03 -0700, Larry Jaques
wrote:

Q: Who here on RCM has 3 spring scales with which they can perform
this experiment?

Yikes! I hadn't been following this thread. Something will give. Dad
used this technique in 1949 or so to unstick some early tracked
combines cutting rice. He'd tie on with 100 ft. of 1" cable, take the
steel wheeled poppin' johnny out and spin it down at the end, then get
in the middle with another tractor and pull sideways. He later
realized that he could have been killed had something let go.

It's just trig. At 0 deg deflection, the load on the ends is
infinite. At 1 deg,you've moved sideways 1.7%, and decreased the
length by 0.015%, so mechanical advantage is already down to 114:1. At
0.1 deg, the mechanical advantage was 1145, and at 0.01 deg, 11,459
and so on. I used sin/(1-cos).

Ah, those are the figures I was looking for. Man, those Cable Rail
style wires take a beating, don't they?

I trode across a suspension footbridge (The Swinging Bridge over the
Illinois River in Kerby, OR) yesterday and admired the engineering.
12x12" uprights about 20' tall and 1" galv steel wire ropes supporting
about an 80' span. I wonder how far they had to sink the terminations
to support that structure. I found a pic already online:
http://www.cavejunction.com/cavejunction/cj-pics.shtml
click on "Swinging Bridge - donated by Poodlenuts"

--
"Most Folks Are As Happy As They Make Up Their Minds To Be"
-Abraham Lincoln
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