On Wed, 10 Sep 2008 18:04:02 -0400, with neither quill nor qualm,
"Mark Dunning" quickly quoth:


wrote in message
...
When applying force perpendicular to a tight wire, the force
multiplies by a large factor.

I don't grok that, Ivan. A pull on the middle of the rope would be
equal on all 3 ends, wouldn't it?

No, this is not a simple straight line mechanics problem of pulleys
acting as levers, it's a vector addition problem. When you pull the
rope out of line at the center, the component of tension perpendicular
at each end of the main rope has to be very high to match the small
component needed to offset the sideways pull, and this approaches
infinity the tighter the main rope gets.

What's the math/law/formula, Mark?


As soon as you begin to pull the main rope out of a striaght line, all
the angles change and your advantage goes way down. This is not
something you can do for a sustained pull, it's a game of inches.
Pull, retension to shrink the angles again, repeat, ad nauseum.

I have successfully used this technique to grunt a car up a incline into a
garage when a pusher vehicle/come-a-long were not available.

Anchor end of rope to immovable object.
tie to a chain with a hook.
Fasten other end of chain to bumper tightly.
Have a helper with a chock ready behind wheels.
Grab the middle of the rope and lean back
Car moves, and helper moves chock.
Release, take another bite on the chain and repeat

Works a treat.

Interesting. Now, after all this, I forgot the OP's intent. g

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