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OT: Mechanical puzzle

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  • #31
    Evan

    As far as more sophisticated configurations go.. without complicating things with Free body diagrams or three dimensional vector solutions... the tension is the same throughout the cable if the system is at rest. If not, there would be motion induced. That is a layman's short cut to the free body diagram of the middle 100 lb wieght supported by the two cables each exerting 50 lbs upward pull. The system is in equilibrium (at rest). For those who are wanting to go further, F=ma=0 at each center of rotation for each pulley and each mass. No acceleration - all forces sum to zero in three dimensions - the system is at rest.

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    • #32
      Nice job, even if their "bump keying" at least you will have them on film leaving with the crap merchandise...

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      • #33
        Cam,

        I know. Net forces must be zero. I posed this because it is generally counterintuitive. This is especially so when you keep adding weight in a new configuration but the tension doesn't change. It is also directly relevant to some designs.

        I asked this question today of an old friend of mine who was also a machinist before he retired and he at first assumed the wrong answer. It's funny how some of the simplest looking problems can be so easy to mistake.
        Free software for calculating bolt circles and similar: Click Here

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        • #34
          {{ machinist before he retired and he at first assumed the wrong answer.}} Actually, you have never met or talked to anyone in the REAL world. Have to feel sorry for you.

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          • #35
            We all live in a world of our own making. Perception is 9/10ths of reality. Some of those worlds are a bit stranger than others, apparently.
            Free software for calculating bolt circles and similar: Click Here

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            • #36
              {{stranger than others, apparently.}}. Yeah, then there's just people with no common sense.

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              • #37
                Sometimes the simplest solution is the best. The trick is to identify which part doesn't change between rig ups.

                Millman

                Common sense, like common courtesy, isn't as common as it used to be or should be....
                Last edited by cam m; 08-09-2006, 01:09 AM.

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                • #38
                  A definition of "common sense"

                  A form of evidence that is based on conventional wisdom, tradition, or someone’s personal philosophy or perspective. It is hard to judge the validity and reliability of common sense because little supporting evidence is involved. Most people judge the validity and reliability of common sense by the person citing common sense as the basis for a decision. However, common sense can be a very biased approach to decision making and means nothing more than “what is common to me makes sense.â€‌



                  Free software for calculating bolt circles and similar: Click Here

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                  • #39
                    Like I said...just repeating what someone else has already said or done.

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                    • #40
                      ike I said...just repeating what someone else has already said or done.
                      So then, how do you learn? Do just make it up as you go along? Or do you study the work that others have said and done? Have you ever opened a textbook?
                      Free software for calculating bolt circles and similar: Click Here

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                      • #41
                        I try to quote from personal experience, text books are only a starting experience for the uneducated. After a while, you do not need the text or pictures to qualify.

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                        • #42
                          The quality of a man's education depends the wisdom of his teachers. This is especially so for the self taught.
                          Free software for calculating bolt circles and similar: Click Here

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                          • #43
                            As usual, you are partially correct. A man's wisdom comes from experience...which there is no substitute. All the books in the world only makes you "well read", however that does not make you smart.

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                            • #44
                              Things must be slow if we get three pages of drawings blocks, strings and pullies instead of making the bloody thing..................

                              .
                              .

                              Sir John , Earl of Bligeport & Sudspumpwater. MBE [ Motor Bike Engineer ] Nottingham England.



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                              • #45
                                the force of tension in the wire is 100 lbs, picture it as a tug of war between the wire , 50 lbs in each direction, the pully in this case is just directing the motion. Another way to think of this is as if instead of 50/50, you then had 70/30 and then 90/10 etc.. until you came really close to 100/0, in that case it would be the simple case of a weight on a straight wire of 100 lbs.

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