Downhill, the hands loose from the steering wheel … and there comes the fatal ‘speed wobble’

Take a light cord or just a string, tie a heavy object like a key or sturdy nut and wave the business above your head around. Do it first in mind. Ask yourself how and in which direction the key will fly away if you release the string. Then take the test at some distance from fragile household effects.

The key follows the turning line on the turning circle, because that is in accordance with the first law of Newton. After the string loosened, only two forces worked on the key: gravity and air resistance and they have little influence on the track within the short test duration. The key persists in the movement he had when the string loosened. In 1980, 83 percent of the psychologists interviewed by psychologists said they had also expected something like that, although 30 percent thought that the flying key would follow a crooked job. He doesn’t do that, he follows a straight tangent. It stood in Science.

Strangely enough, only 6 percent of psychology students thought that the key would fly away in the radial direction, so straight from the circle center. That was precisely what the AW editors initially seemed like plausible: the way that had always blocked the pulling force in the string. You have nothing to do with intuition.

Twenty -five years after the string test asked American psychologists To American psychology students which balls from a collection of equally large plastic balls would fall the fastest: the light or the heavy. 39 percent of students, including a lot of boy psychology students, replied that they were just as hard would fall. Heaven knows why, a normal person, just like Aristotle, would assume that the heaviest faster. The boys’ students perhaps suspected a dirt or had a vague memory of a statement by Galilei.

In reality, the heavy balls are the fastest, the air resistance has relatively slightly less influence on it. But the air resistance feel Of course not if you have the balls in your hand, the weight is. You also do not get the speed difference easy to see unless you let the balls roll from a weakly sloping surface. But then the effect of the air resistance is only reflected when the slope is sufficiently long. Inner rooms it will be nothing.

Medieval views

A person does not easily come through mere experience to correct and useful insights, that is the Take Home Message which we already announce here. It is also determined in the nice field that ‘naive physics« is mentioned. People who never received physics education in the explanation of the world in misunderstandings, wrong assumptions and medieval views and tries to find some system in that physics. It is a painful sight.

It is therefore with some embarrassment that the adult who did receive physics education today thinks back to that time he cycled a long slope with his children in mountainous areas, without kicking it, and was surprised by the observation that he came across the adolescents considerably faster. The astonishment went so far that there was even a bicycle to see if it might have been there – they were ordinary city bikes. But enough about this!

By making himself wide and to sit up as much as possible, where he had to let go of the steering wheel, the adult preserved was able to temper the pace of his descent. Until he had to grab the steering steering again because the front wheel of his bike started swabbing back and forth like a raging back and forth and there was a danger of derailment.

Shimmy is it hot, or speed wobbleand the average city cyclist may know the phenomenon exclusively from shopping carts with a hysterical front wheel. But YouTube has many examples of cyclists and motorcyclists who are hit by a shimmy. Especially for motorcyclists, the phenomenon is extremely dangerous, they call A Fatal Shimmy An tank weaker.

On the internet it is not about tips to get out of a dangerous shimmy. The fear of the Shimmy is that scientists often close their articles about the shimmy of the racing bike with highly personal advice: very cautiously brakes and, above all, reduce sailing by standing up and increasing the air resistance. Others recommend going out of the saddle and clamping the horizontal frame tube between the knees. (Closing mouth and eyes is not necessary.)

Interesting is that of a cycling platoon That a descent is often only one rider is hit by a shimmy. That is the main feature of the phenomenon: the randomness, a cyclist does not easily generate a shimmy on command. At least must be its speed above 45 km/h, and then it is still waiting for the correct disruption that front wheel and fork can ‘catch’. It can come from an indulgence or a relocation of the rider.

The frequency with which the front wheel will swab lies with almost all racing bikes around 7 Hertz (seven fluctuations per second), which is too fast to be able to control it. The driving speed has no influence on it, because shimmyen is a resonance phenomenon: the frequency is a characteristic of the combination frame and rider. The vibration is maintained by the kinetic energy of the bicycle.

It seems certain that there are frames can be designed that will not resonate under normal circumstances. The research on this, as comes into the picture with Google Scholar, is of a level that even many non-naive physicists will be too high.

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