At 09:32 PM 4/2/99 -0700, you wrote:
>
>This is interesting discussion. Consider the following
>simple setup:
>
>Take a standard gin pole, run the rope through the pulley,
>but instead of attaching the rope directly to the load,
>run the rope through a second free pulley, which is attached to
>the load. Now run the end of the rope up to the top of the
>gin pole, and firmly secure it to the top of the gin pole mast
>somehow. Now attempt to lift a 100# mast.
>
This is SIMPLE 2:1 mechanical advantage system.
>The 100# is supported by two ropes, so the tension on the rope
>is 50#. Tension on the rope is constant in a pulley system, so
>the people on the ground are exerting another 50#
Wrong. The haul line is seeing 50# less. Thats why they call it a
mechanical advantage system. So where did it go? You anchored one
end to the top of the Gin pole. Now it is supporting 50# and the other
line has the other 50#. ( this is the 50# that the haul crew is seeing.)
>downward tension, and the resultant downward force on the gin
>pole is 150#, instead of 200#, which it would have been if the
>second pulley had not been used.
The force on the GIN POLE will always be twice the load.
As a general rule. Traveling pulleys create mechanical advantage.
fixed pulleys do not. They only change the direction.
another rule of thumb is to count the number of lines at the load.
this will usually give you your M/A in Simple systems.
I'm not a physics teacher nor do I claim to be an expert but I do
have several years of experience in simple, compound, and complex
M/A systems used in Structural, High Angle, and Confined Space
Rescue systems. Just please understand what your trying to do
before you do it. Our hobby can be a lot of fun but some of these
things can be dangerous if not thought out properly. SAFTY FIRST!
Gentle flames only please <G>
KK5LC
Shane Dugas
Prairieville, LA
Shane@eatel.net
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