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Thread: tug of war

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    tug of war

    2 teams are having a tug-of-war. There are 5 people on each team, 10 in total. Each person pulls exactly 100 pounds, so the tug-of-war is at a stalemate. (at least for now) How much force is being exerted on the rope? (note, this is NOT a trick question.) Think about it before going to the next post for the answer.

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    If you answered 1000 pounds you are incorrect. I know it seems to defy logic, but the correct answer is 500 pounds. One of the teams is indeed pulling 500 pounds, but the other team is pulling only to cancel the 500 pounds, not to add to it. To put it another way, if one end was tied to a tree, the force would be 500 pounds, right? so one of the teams is acting like the tree... its only anchoring the rope, just like the tree...bingo...500 pounds. (ok i'm bored... any other "amazing" facts or brain teasers out there?)

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    That Boy Ain't Right Blake's Avatar
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    Actually, I would have said Zero, since both teams are exerting equal force in opposite directions.

    If at some point one team finds the strength to pull an extra hundred pounds, they will win, but only by 100 pounds.
    Light travels faster than sound, which is why some people appear brighter before you hear them speak.

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    Zero? that would be some rope... it would withstand an infinite force, as long as the pull was equal in both directions. We could restring nylor with it..:D

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    6920. Figures = 1/8 horsepower per man. While a man can pull only his own weight vertically. Horizontally it depends on his own strength (average man 1/8 horsepower, and yes, I realize he average man is over 100 lb) his traction (if he digs in he can get more than his weight in traction) and determination which cannot be evaluated.

    Chip

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    That Boy Ain't Right Blake's Avatar
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    Quote Originally Posted by Dave Nelson
    Zero? that would be some rope... it would withstand an infinite force, as long as the pull was equal in both directions. We could restring nylor with it..:D
    Well that would be cool, but it was not my point. Any given rope will have a finite tensile strength, which would depend on its material, size and possibly other conditions. In the tug of war, we assume the force being exerted to be less than what would break the rope. Otherwise at the instant the rope breaks, each team is exerting 500 lbs on their end and the other end (each broken end) is exerting zero lbs. The result is that each team member falls into the mud!

    I'm interested to know where your 500 lb value came from. My initial answer came off the top of my head, but I verified it through an old physics test I have lying around (which actually uses a tug-of-war to demonstrate the concept of equilibrium). It's from the 1930's, so I suppose it's possible the laws of physics have changed since then.

    :cheers:
    Light travels faster than sound, which is why some people appear brighter before you hear them speak.

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    Bad address email on file Mikef's Avatar
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    Another strange fact is:


    The word gullible is not found in any English dictionary

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    Quote Originally Posted by Dave Nelson
    If you answered 1000 pounds you are incorrect. I know it seems to defy logic, but the correct answer is 500 pounds. One of the teams is indeed pulling 500 pounds, but the other team is pulling only to cancel the 500 pounds, not to add to it. To put it another way, if one end was tied to a tree, the force would be 500 pounds, right? so one of the teams is acting like the tree... its only anchoring the rope, just like the tree...bingo...500 pounds. (ok i'm bored... any other "amazing" facts or brain teasers out there?)
    Surely your example would be the same as 10 people pulling against a tree?
    As unlike the tree they are pulling with equal but opposite force.

    You're giving me a headache.

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    Master OptiBoarder OptiBoard Gold Supporter Judy Canty's Avatar
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    Quote Originally Posted by Mikef
    Another strange fact is:


    The word gullible is not found in any English dictionary
    http://www.m-w.com/dictionary/gullible



    Found it! :bbg:

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    I still believe a determined man in good condition can pull a lot more than his own weight. He may not be able to lift same with a pully but dug in on a straight line, I think his force could be several times his own weight.
    I know that one can move more (dragging it than ones own weight).
    And I also know that many of us carry more than our own weight on the job every day. This may ballance out for those that don't carry thier own load but some are more capable than others.

    Chip

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    Bad address email on file Mikef's Avatar
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    Quote Originally Posted by Judy Canty
    Judy

    I hope you understand the joke!

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    I have some 'splainin to do. OK lets say a team of guys are pulling a rope down the street. For arguments sake we'll just say everybody can pull 100 lbs. A guy sees this group taking a rope down the street, so he grabs the other end of the rope, and applys his 100lbs. The original 5 guys find it now a bit more difficult to pull the rope along, but still no problem: they only have to apply 100 lbs (or slightly more) to keep moving the rope, dragging the poor guy along. When his friends see him being dragged along, 2 of them join him. now 5 guys are dragging 3. It takes the 5 guys 300 lbs (or slightly more) to keep dragging the three along, which means there is 300 lbs on the rope. Soon 2 more guys join the three, and are now able to apply enough force to stop the first 5 from dragging the rope any further: There is now 500 lbs on the rope, not 1000. This was taught to me by an engineer who specialised in rope rescue systems for mountain rescue during a mountain rescue course I took some years back.

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    Pomposity! Spexvet's Avatar
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    Would this also be correct, then?

    There's a 1,000 pound weight on the ground. Attached to it is a rope. Standing on a platform, above the weight, are 5 men, each of whom can pull 200 lbs. The men grab the rope and lift the weight. There's 1,000 lbs on the rope. Two more men join the first 5. There's still only 1,000 lbs on the rope, right?
    ...Just ask me...

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    One 250 lb. can pull a 1000 lb. wt., then cannot 2 or more pulling in opposite directions put 2000 lb. on the rope? Pulling "dead wt." and pulling force are not exactly related.With some of the earlier deffintions, breaking a 1000 lb. rope with less than 1000 pounds of force could not be broken. Force on the rope can also be altered by the velocity of the force (ft/lbs).

    Chip

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    Maybe we'll have to ask one of those engineers we have so much fun joking about.:D Spexvet you are correct. Chip, if 1 guy is pulling 1000 lbs on a rope that is tied to a tree, the force on the rope is 1000 lbs. If another guy then begins pulling on the rope to relieve the stress on the tree, He will need to "match" the 1000 lbs to relieve the stress on the tree. When he relieves all the stress on the tree, he will now be pulling 1000 lbs to counter the first guy. The first guy, however, is NOT pulling any harder than he was in the first place-thus the stress on the rope remains the same:1000lbs. Now to say the force on the rope has doubled requires the first guy to have increased his pulling force on the rope... you can't say the force has increased without saying the first guy has to pull harder.. but he doesnt, he may not even be aware the tree has been replaced by another guy. Bingo, force on rope remains the same. Now if these 2 guys wanted to put 2000 lbs pull on the rope, they would both pull the same direction, and let the tree hold the other end. Now I'M going to make like a tree and LEAVE.:hammer:

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    Dave:
    I guess what I'm trying to say is that two one hundred pound men dug in andpulling on a rope in oppositon to each other can exert a lot more than one hundred pounds (or even more than 200 lb.) of pull (assuming they are in good condition, determined and trying).


    Chip

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    I neglected to mention that all the people in this exercise are engineers: they are only capable of 100 lbs pressure.;)

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    Oh! That's a lot different than Salesmen or Soldiers.

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    Quote Originally Posted by Spexvet
    Would this also be correct, then?

    There's a 1,000 pound weight on the ground. Attached to it is a rope. Standing on a platform, above the weight, are 5 men, each of whom can pull 200 lbs. The men grab the rope and lift the weight. There's 1,000 lbs on the rope. Two more men join the first 5. There's still only 1,000 lbs on the rope, right?
    Well, if five men (or women) capable of lifting 200 lbs each are pulling on a rope attached to a 1000 lb weight, all they will do is take the slack out of the line. But when their friends arrive and lift with all their might, the weight will be lifted, due to the extra 400 lbs of upward force (about 350 Canadian :D ). However, the downward force on the rope will still be 1000 lbs, courtesy of its mass and gravity.

    If the rope is tied to a tree and you pull on it with 100 lbs of force, the tree will provide 100 lbs of resistance. If it provided no opposing force, you would pull away both the rope and the tree!
    Light travels faster than sound, which is why some people appear brighter before you hear them speak.

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