I saw in the film (based on a true story) "The walk" a guy who tried (and succeeded) to go from one high building to another via a rope. He even succeeded in going from one the (then still existing) two Twin Towers to the other and the other way round. He carried with him this long stick. You´ll probably all know what I mean.

Why gives this more stability? Has the flexibility of the stick something to do with it? I can imagine that with a stiff rod it's much harder to do.


Flexibility plays no role, because the rod can be naturally bent.

If the walker has no rod and his CoM is not aligned to the rope he hasn't a big chance of adjusting it.

A rod contributes to the mass of the system (and the position of CoM) and distribute mass on a greater extension, and the man can shift it sideways or rotate it. Angular momentum mvr = L of the rod is a powerful tool to adjust his CoM: he can "lean" on it and pushing it one way makes his body rotate in the opposite direction.

A heavy rod also lowers the center of mass and makes the body on the rope more stable. The longer (r)/heavier (m) the rod, the greater is L, and the greater the push he can apply to his own body

enter image description here

If the rod were curved just a little below the rope (not in the above picture, of course) and had some ballast at both tips, then the walker could never fall down, if he lost his balance the ballast wpwould bring him up again.(, as long as he does not slip off the rope)


rob has misunderstood the picture and his comment has provoked the downvotes. No worries. The center of mass in the picture is much lower then the CoM of the walker, therefore the whole system is more stable. enter image description here

If he carried same rod wit same inertia, but in a higher position , he would be even less stable enter image description here

than he would be with no rod at all, and he would easily fall down

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    $\begingroup$ The walker in your image clearly has his entire mass, and therefore his center of mass, above the rope. $\endgroup$ – rob Jul 7 '16 at 17:47
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    $\begingroup$ @rob, so what? Of course he can fall $\endgroup$ – user104372 Jul 8 '16 at 5:53
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    $\begingroup$ I'm not denying that the configuration in your second picture would be more stable than in the first picture. But tightrope walkers don't walk like that. Making charitable guesses about mass of the balance bar, the walker in your first photo has moved his center of mass from his navel to his thigh. ... Next time you are trying to balance on a curb or playground balance beam or whatever, you'll notice that you're more stable with your arms stuck out than with them at your sides. But you lifting your arms raises your center of mass, contrary to the model you present here. $\endgroup$ – rob Jul 8 '16 at 12:22
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    $\begingroup$ You missed the point of the third picture (and of the whole answer), which is to disprove your point that larger inertia (and time) is the purpose, which is not true. The purpose of a rod is to lower CoM and, secondly, to spread the mass. The second picture is just an exaggeration of the first and shows that lowering CoM, pushed to the limits) can work wonders, which large inertia can't do. I hope you eventually got it ! $\endgroup$ – user104372 Jul 9 '16 at 7:56
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    $\begingroup$ @user104372: try balancing a pencil on end on your finger. Now, try balancing a broomstick on end on your hand. Which is easier? The broomstick is much easier because you need a much slower reaction time to do it. The importance of reaction time for the tightrope walker works exactly the same way. $\endgroup$ – Peter Shor Aug 1 '16 at 16:33

A long rod, especially with additional masses at both ends, has a large moment of inertia and therefore can change its angular velocity only slowly. This means that if the walker gets off-balance, there is more time available to correct before he falls.

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  • $\begingroup$ Comments are not for extended discussion; this conversation has been moved to chat. I also deleted a few moderately inappropriate comments. $\endgroup$ – David Z Jul 9 '16 at 12:28
  • $\begingroup$ Slow change of angular velocity is not the main advantage of a rod, actually it plays a marginal role. Wiki is in a way misleading, since it does not list them in a proper order: "...a wire-walker may use a pole .. or may stretch out his arms ...This technique provides several advantages. It distributes mass away from the pivot point, thereby increasing the moment of inertia. This reduces angular acceleration .... The result is less tipping. In addition the performer can also correct sway by rotating the pole." $\endgroup$ – user104372 Jul 10 '16 at 4:06

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