Monkey on a Rope

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  • gsmittle
    Veteran Member
    • Aug 2004
    • 2784
    • St. Louis, MO, USA.
    • BT 3100

    Monkey on a Rope

    Snagged this one from the Straight Dope website:

    A rope is suspended on a pulley. At one end is a monkey is holding on to the rope. At the other end is a bucket of sand with equal weight - equilibrium. If the monkey started to climb the rope - what would happen?

    g.
    Smit

    "Be excellent to each other."
    Bill & Ted
  • leehljp
    Just me
    • Dec 2002
    • 8429
    • Tunica, MS
    • BT3000/3100

    #2
    IMO, He would climb it, nothing would happen to the weight until the monkey jumped over to the rope with the weight on it, then he would ride the rope down.
    Hank Lee

    Experience is what you get when you don't get what you wanted!

    Comment

    • Denco
      Guest
      • Mar 2003
      • 426
      • Coming soon: California
      • BT3100

      #3
      It depends.....does the monkey have a permit?
      *****Measure twice, cut once.....rats, back to the lumber yard.*****

      Comment

      • TB Roye
        Veteran Member
        • Jan 2004
        • 2969
        • Sacramento, CA, USA.
        • BT3100

        #4
        As he climbed the rope the bucket of sand would rise to maintain the equilibrium. I think.

        Comment

        • woodturner
          Veteran Member
          • Jun 2008
          • 2047
          • Western Pennsylvania
          • General, Sears 21829, BT3100

          #5
          Originally posted by gsmittle
          A rope is suspended on a pulley. At one end is a monkey is holding on to the rope. At the other end is a bucket of sand with equal weight - equilibrium. If the monkey started to climb the rope - what would happen?
          Is this an "ideal" monkey or a real monkey? A real monkey climbing the rope would exert additional force on the rope, causing the sand to rise. An ideal monkey could traverse the rope without increasing the force and should be able to be stable at a higher position. Assuming earth gravity, it does vary with distance but the difference is so small for a few feet difference that it would have no impact on the stability. In other words, the force is essentially the same regardless of where the monkey is on the rope, so the sand should remain in the same position.

          That's always the problem with these kinds of thought experiments - they don't specify the conditions completely enough to allow only one "right" answer, and people reach different conclusions based on different assumptions.
          --------------------------------------------------
          Electrical Engineer by day, Woodworker by night

          Comment

          • cabinetman
            Gone but not Forgotten RIP
            • Jun 2006
            • 15218
            • So. Florida
            • Delta

            #6
            I know the answer, but I won't spoil the guesswork. You could use a formula.

            .

            Comment

            • LCHIEN
              Internet Fact Checker
              • Dec 2002
              • 20914
              • Katy, TX, USA.
              • BT3000 vintage 1999

              #7
              this is one of those problems where you ignore the friction of the pulley and the weight of the rope. Also as someone pointed out any height difference will change the relative gravity a bit but we should ignore that also.

              Some key physical laws are at work.
              1. Conservation of momentum
              2. Conservation of energy
              3. conservation of inertia (Newtons 1st law)
              4. F=ma (newton's second law)
              5. for every action there is a second and equal opposite reaction (newt's 3rd law)
              Loring in Katy, TX USA
              If your only tool is a hammer, you tend to treat all problems as if they were nails.
              BT3 FAQ - https://www.sawdustzone.org/forum/di...sked-questions

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              • cabinetman
                Gone but not Forgotten RIP
                • Jun 2006
                • 15218
                • So. Florida
                • Delta

                #8
                Originally posted by LCHIEN
                this is one of those problems where you ignore the friction of the pulley and the weight of the rope. Also as someone pointed out any height difference will change the relative gravity a bit but we should ignore that also.

                Some key physical laws are at work.
                1. Conservation of momentum
                2. Conservation of energy
                3. conservation of inertia (Newtons 1st law)
                4. F=ma (newton's second law)
                5. for every action there is a second and equal opposite reaction (newt's 3rd law)
                So, what say you?

                .

                Comment

                • Stytooner
                  Roll Tide RIP Lee
                  • Dec 2002
                  • 4301
                  • Robertsdale, AL, USA.
                  • BT3100

                  #9
                  He would lift the sand. He has the advantage on the pulley.
                  Last edited by Stytooner; 07-24-2013, 10:02 AM. Reason: speeellin
                  Lee

                  Comment

                  • TB Roye
                    Veteran Member
                    • Jan 2004
                    • 2969
                    • Sacramento, CA, USA.
                    • BT3100

                    #10
                    On second though, I will have to consult my Attorney.

                    Comment

                    • pelligrini
                      Veteran Member
                      • Apr 2007
                      • 4217
                      • Fort Worth, TX
                      • Craftsman 21829

                      #11
                      Without making any other assumptions (frictionless pulleys, weightless ropes, etc) my gut impression tells me that the bucket will get pulled up slightly as the monkey starts to climb. The monkey will be exerting a force on the rope in order to pull itself up. Even though the bucket and the monkey and rope are at equilibrium at rest I don't think the buckets mass will totally resist the force of the monkey pulling itself up the rope. I don't think that the monkey would remain in the same place when it starts to climb, height wise.

                      If that is correct, then the bucket will get pulled up the rope quicker and quicker due to the weight of the rope now being on the other side of the pulley.
                      Erik

                      Comment

                      • capncarl
                        Veteran Member
                        • Jan 2007
                        • 3564
                        • Leesburg Georgia USA
                        • SawStop CTS

                        #12
                        Having observed lots of monkeys climbing ropes, I'd say that the monkey would climb the rope until he felt it coming down, then he would grab the other rope and climb them both until he reached the pulley. Then the monkey trainer would have to get a ladder and go get the monkey out of the rafters.
                        capncarl

                        Comment

                        • leehljp
                          Just me
                          • Dec 2002
                          • 8429
                          • Tunica, MS
                          • BT3000/3100

                          #13
                          Originally posted by LCHIEN
                          this is one of those problems where you ignore the friction of the pulley and the weight of the rope. Also as someone pointed out any height difference will change the relative gravity a bit but we should ignore that also.

                          Some key physical laws are at work.
                          1. Conservation of momentum
                          2. Conservation of energy
                          3. conservation of inertia (Newtons 1st law)
                          4. F=ma (newton's second law)
                          5. for every action there is a second and equal opposite reaction (newt's 3rd law)
                          This is what went through my mind, but I considered it basically negligible. Swinging momentum will still balance out; same weight on both sides still balances out since you can't shorten the rope . . .

                          IF IF as he climbed, the bucket would basically go up with him because the momentum would pull up the bucket minisculely, and as he did, the rope would be shorter on the bucket side than the monkey side. Would not the rope on the monkey side be the difference in pulling the bucket up?

                          I just read what Erik said; same thing for me, IMO.
                          Hank Lee

                          Experience is what you get when you don't get what you wanted!

                          Comment

                          • dkerfoot
                            Veteran Member
                            • Mar 2004
                            • 1094
                            • Holland, Michigan
                            • Craftsman 21829

                            #14
                            Before or after the monkey pooped in his hand and threw it at you?

                            .
                            Doug Kerfoot
                            "Sacrificial fence? Aren't they all?"

                            Smaller, Smarter Hardware Keyloggers
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                            KeyLlama.com

                            Comment

                            • annunaki
                              Senior Member
                              • Jan 2008
                              • 610
                              • White Springs, Florida
                              • 21829, BT3100, 2-BT3000(15amp)

                              #15
                              All Primates perspire, and as such as he exerted himself and perspired, it would evaporate, thus decreasing his body weight, and the pail lowering. Since no mention is made of the length of the rope, an infinite length allows for an infinite amount of exertion and perspiring which will eventually result in the monkeys hands becoming drawn into the pulley and mangled (unless he gets spooked and flees), thus trapping him there until such time as he expires.
                              http://en.wikipedia.org/wiki/Fileodecahedron.gif

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