Crazy Knot – Science Spectrum

Unlike the nut on a threaded rod, here we are dealing not with sliding but with a real rolling action. This means, as with the wheels of a car, that the point at which the cylinder sits on the ground covers a distance with each revolution corresponding to the length of the circumference. An ordinary wheel is always located only in one place on the board. On the other hand, the twisted knot touches the stick in three different places. In other words, three lanes roll at the same time.

© H. Joachim Schlichting (Detail)

Snapshot on tape | The knot is spinning down a wooden stick.

The rolling motion of the knot inevitably means that it cannot be a rigid structure. It retains its external shape and appears to be at rest as a whole during rotation. However, in reality, the knot bar is meandered by its own shape, so to speak. If you mark a point on the winding knot, you can see how it periodically rotates around it.

Amazing physics hides behind many everyday objects. I felt for many years Hans Joachim Schlichting He discusses these phenomena and explains them in his column for readers of the “Scientific Spectrum”. Schlichting is Professor of Educational Physics and worked at the University of Münster until his retirement.

The drive of all is the weight of the node. With a straight stick, pull ends down at the floor. Continuous movement can be achieved by using a large ring of appropriate thickness as a guide instead. Then the hoop is rotated in the opposite direction to the rotating knot as quickly as the latter loses its height.

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Animated valet knot (GIF)

© H. Joachim Schlichting

The direction of the axle changes with the height of the node on the bent ring. In turn, only a large or less element of attractiveness plays the role. The node only benefits from its full effect when the axis of rotation is aligned vertically, that is, it rotates in a horizontal position. Here it reaches the maximum rotational speed.

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