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  • z rig 3;1 and 5;1

    why they call it 3;1, 5;1 mechanical advantage? is because the hardware or is because pull 3 feet and move the load 1 feet. i really want to find out why...thank you
    Last edited by ffgdog; 08-08-2010, 02:29 PM.

  • #2
    The ratio given in a mechanical advantage relates to the amout of force applied then muliplied thru your system and applied to your load. A 3:1 MA indicates that the amount of force applied will generate 3 times the force on the load. So it would take 9 guys pulling on a 1:1 to generate the same result of 3 guys pulling on a 3:1. Of course this is all theoretical because some of the force is lost in the hardware (pulleys). So a 3:1 will not give you a true 3X force mulitplier, but close.

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    • #3
      thank you......

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      • #4
        Wow Hook, how did you understand what the question was?
        Career Firefighter
        Volunteer Captain

        -Professional in Either Role-

        Originally posted by Rescue101
        I don't mind fire rolling over my head. I just don't like it rolling UNDER my a**.

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        • #5
          Originally posted by ffgdog View Post
          why they call it 3;1, 5;1 mechanical advantage? is because the hardware or is because pull 3 feet and move the load 1 feet. i really want to find out why...thank you
          You are correct in that a 3:1 system you will pull 3' of rope to move the object 1'. The greater the mechanical advantage the more rope you are going to need.

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          • #6
            Originally posted by BKDRAFT View Post
            You are correct in that a 3:1 system you will pull 3' of rope to move the object 1'. The greater the mechanical advantage the more rope you are going to need.
            Actually, that is incorrect. Rope distance or length has no bearing on mechanical advantage. It is the number of pulleys in the system and how they are attached that gives you the mechanical advantage.

            FM1
            I'm the one Fire and Rescue calls, when they need to be Rescued.

            Originally posted by EastKyFF
            "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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            • #7
              Whenever you pull a rope that is attatched to an anchor thru a pulley you have a 2:1 mechanical advantage over anything attatched to that pulley.
              Last edited by Blulakr; 08-08-2010, 11:02 PM.
              My wise and profound comments and opinions are mine alone and are in no way associated with any other individual or group.

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              • #8
                Originally posted by Blulakr View Post
                Whenever you pull a rope that is attatched to an anchor thru a pulley you have a 2:1 mechanical advantage over anything attatched to that pulley.
                Huh?

                A rope through a single pulley offers no mechanical advantage. its merely a change of direction.

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                • #9
                  Originally posted by Blulakr
                  Whenever you pull a rope that is attatched to an anchor thru a pulley you have a 2:1 mechanical advantage over anything attatched to that pulley.
                  BEEP.... That is incorrect!!!

                  Have a look here to see how MA actually works. And so you know, friction adds a loss of MA when you add more pulleys.

                  http://en.wikipedia.org/wiki/File:Four_pulleys.svg

                  And so you know, I have an engineers license on lifting and hoisting.

                  FM1
                  I'm the one Fire and Rescue calls, when they need to be Rescued.

                  Originally posted by EastKyFF
                  "Firemens gets antsies. Theys wants to goes to fires. Sometimeses they haves to waits."

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                  • #10
                    In the cited drawing, the single pulley rig shows that Fz=Fl - exactly the same force is required to lift the load as the load weighs. Maybe I'm missing something, but to me, mechanical advantage implies that some lesser force will be required to move a given weight (Fz< Fl).

                    Examples 2, 3, and 4 show mechanical advantage.
                    Opinions my own. Standard disclaimers apply.

                    Everyone goes home. Safety begins with you.

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                    • #11
                      Lets make it easy. Lines to LOAD. Anything else is merely a change of direction. If you have 4 lines to the load,you're 4 to 1.If you have 5,5 to 1. Whatever your load is,divide by the load lines and yo have your input. Of course fleet angle and bloack loss figures in but only if you're a purist will you take the time to break it down that far. T.C.

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                      • #12
                        Originally posted by Rescue101 View Post
                        Lets make it easy. Lines to LOAD. Anything else is merely a change of direction. If you have 4 lines to the load,you're 4 to 1.If you have 5,5 to 1. Whatever your load is,divide by the load lines and yo have your input. Of course fleet angle and bloack loss figures in but only if you're a purist will you take the time to break it down that far. T.C.
                        or... you can get a Metz!
                        ‎"The education of a firefighter and the continued education of a firefighter is what makes "real" firefighters. Continuous skill development is the core of progressive firefighting. We learn by doing and doing it again and again, both on the training ground and the fireground."
                        Lt. Ray McCormack, FDNY

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                        • #13
                          Gotta Love It..............

                          Originally posted by Blulakr View Post
                          Whenever you pull a rope that is attatched to an anchor thru a pulley you have a 2:1 mechanical advantage over anything attatched to that pulley.

                          When you pull a Rope that is attached to an Anchor, You're not accomplishing anything except annoying the Anchor.........



                          Actually, after reading your Post the Third time, I see your point. However, the single line gives no advantage. You can connect a Rope to an Anchor, run it thru a Pulley (Block, when using Rope) attached to the Load, THEN RUN IT BACK THRU A SECOND PULLEY ATTACHED TO THE ANCHOR to gain a 2 to 1 Advantage......... End Result is I'm Calling Tim for a Crane to handle it......
                          Last edited by hwoods; 08-09-2010, 11:25 AM.
                          Never use Force! Get a Bigger Hammer.
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                          Chief Earle W. Woods, 1912 - 1997
                          Asst. Chief John R. Woods Sr. 1937 - 2006

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                          • #14
                            Originally posted by hwoods View Post
                            When you pull a Rope that is attached to an Anchor, You're not accomplishing anything except annoying the Anchor.........



                            Actually, after reading your Post the Third time, I see your point. However, the single line gives no advantage. You can connect a Rope to an Anchor, run it thru a Pulley (Block, when using Rope) attached to the Load, THEN RUN IT BACK THRU A SECOND PULLEY ATTACHED TO THE ANCHOR to gain a 2 to 1 Advantage......... End Result is I'm Calling Tim for a Crane to handle it......


                            Harve, how many pullies do you have on your boat to raise or lower the anchor??

                            Plus some anchors I've seen shouldn't be on the TV!!

                            Stay Safe and Well Out There....

                            Always remembering 9-11-2001 and 343+ Brothers

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                            • #15
                              Originally posted by FIREMECH1 View Post
                              Actually, that is incorrect. Rope distance or length has no bearing on mechanical advantage. It is the number of pulleys in the system and how they are attached that gives you the mechanical advantage.
                              Not to be argumentative, but it may be the number of pulleys (and how they are arranged, naturally) that provide the mechanical advantage, but a result of running line through all those pulleys is that you have to pull proportionately more line at the running end to move the standing end. That difference corresponds directly with the mechnacal advantage of the system. i.e. in a 4:1 rig, you need to pull 4 feet on the running end to move the load at the standing end 1 foot.
                              "Nemo Plus Voluptatis Quam Nos Habant"
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                              The Code is more what you'd call "guidelines" than actual rules.

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