Portlandjib.com
new crane
 

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I tried getting away from bridges and cranes ( I have enough of those already), so I thought I'd design a building. I used lots of #6 and #4 beams to build a 4ft tall structure. But then I let the uppermost beam project out beyond the edge of the building and now it looked like a boom. Then all I had to do was to add a hook,line and windlass and --presto--another crane.
  

Now let's say I add more weight to the bucket to make the load 30 pounds (30#). With only the single line (string) it will take  30# of muscle to lift the load. So I added a small pulley and even though it's still only 1 line, because of the way I connected it or (rigged it ) there are now 2 parts of line supporting the load.

Look at the 2 lines going to the pulley supporting the load-  the 2 lines each support half of the load and 1 of the lines is attached to the boom. In other words, the boom is supporting half the load, which means the other 15# of the load is held up by the other line which goes over the white plastic sheave (pulley) in the end of the boom- then over a 2nd sheave in the middle of the tower and finally down to the windlass.    Now when Coleman lifts the bucket he only needs 15# of muscle (forgetting about friction) . We call that MECHANICAL ADVANTAGE.  

You've all heard of Newton's 3 laws. Less well know is Apatov's 4th law---THERE IS NO FREE LUNCH.           Yes the effort or the muscle needed to lift the load is cut in half, but that means now Coleman has to pull in twice as much line to do the job. If he wants to lift the bucket 1 foot off the ground, he'll have to turn the windlass enough times for 2 FEETof line to be  reeled in and wound around the barrel of the windlass.---  NOTHING'S FREE