Random Movements

Supposedly, research has revealed that random movements help explain how a tightrope walker stays aloft, for instance. If understood, robotics engineers could make their machines more stable by injecting a little noise into their systems. And persons having difficulty walking may be able to let some noisy vibrating shoe soles help them walk confidently again. What could be the physics here?

Answer

Wobbles in any system can be followed with fast cameras. For most human actions, from balancing a stick vertically on a finger to balancing on a tightrope, wobbles occur that last from seconds to tens of milliseconds. Usually the shorter the fluctuation, the more of them there are. But the typical human reaction time for such balancing acts is about 100 milliseconds, so most of the wobbles are faster than humans can react. Mathematical modeling of human balancing acts match the measured fluctuations only when the person or object is on the verge of falling. Then the random fluctuations cancel each other out and the object remains upright.

Related research has found that elderly people and others with balance problems showed signs of better balance when they stood on a pair of battery operated, randomly vibrating insoles. The idea is that these vibrations amplify balance-related signals from the feet to the brain and vice versa that may have become reduced by age or illness. When people walk, then turn or reach, they are most vulnerable to a fall. When a person leans or sways to one side, the pressure on the sole of that side increases, and the nervous system senses the change in pressure and sends a message to the brain so that the posture can be adjusted. In many people, those messages can be altered by age, stroke, or conditions such as diabetes. Further testing is under way to optimize these helpful insoles.

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