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Have you noticed that if you take your mouse and hang it from the end it will start to twist until it becomes untwisted? My puzzle is this:

If you have a really long rope and not enough vertical space, how do you untwist it?

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    $\begingroup$ This sounds like a lifehacks question instead of a puzzling question. $\endgroup$ – Sumurai8 Jul 9 '17 at 12:32
  • $\begingroup$ I suspect the unwritten constraint is that the solution must allow the rope to untwist 'on its own' under gravity. Manually untwisting it doesn't seem to fit the intent of the question. Can you please confirm / deny / elaborate? $\endgroup$ – Lawrence Jul 10 '17 at 2:40
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You grab one end, and

a meter from that you roll up the remaining rope, then fixate it and let the knot hang.

Consider the first meter fully untwisted. Open the knot, grab the rope where the knot was, roll up the remaining rope another meter apart. Repeat till you untwisted it all, meter by meter.

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  • $\begingroup$ This is an inappropriately naughty answer.    :-)    ⁠ $\endgroup$ – Peregrine Rook Jul 10 '17 at 17:26
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If you don't have enough vertical space, then perhaps

Find somewhere with plenty horizontal space, and bring a friend. Then, you grab one end, and your friend grabs the other. Then you both pull until the rope is untwisted.

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  • $\begingroup$ That might just tie a knot though $\endgroup$ – Beastly Gerbil Jul 9 '17 at 14:29
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    $\begingroup$ @BeastlyGerbil I thought the rope was initially twisted, not tangled. If it was tangled, then hanging it vertically would also result in a knot. $\endgroup$ – MikeQ Jul 9 '17 at 15:04
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Building on @Mike Q's answer,

Before grabbing one end, attach a spring to the other end of the mouse , and then fix a spring to a rigid, immovable body such that the spring is stretched (and has enough force constant to be able to pull on the mouse and the rope).

This is because

the human's hands might not be a very reliable constant, uniform force in the same direction.

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