Those who have studied cooling fans may find a very regular phenomenon-whether the number of cooling fan blades is 3, 5 or 11, it is often an odd number.

This is because if the number of blades of the fan is an even number, and a symmetrical arrangement is formed, the balance of the fan itself will be difficult to adjust.

In fact, the biggest reason is to reduce resonance. The absolute balance of the fan blade does not exist. When the cooling fan is running at high speed, more resonance will be generated. Long-term operation will cause the fan blade to be unable to withstand the fatigue caused by the resonance, and eventually the fan blade may break.

Some people think that the fan blade fracture is a bit too exaggerated. In fact, you underestimate the destructive nature of the resonance phenomenon.

Bridge collapsed

In the middle of the 18th century, a group of soldiers passed by on a 102-meter-long bridge in Angers, France. When they crossed the bridge in neat steps under the command of the commander, the bridge suddenly broke, killing 226 soldiers and pedestrians.

At the beginning of the 19th century, under the command of the commander, a group of Napoleonic soldiers passed a bridge in Angers, France, with mighty, majestic and uniform steps. When I walked quickly to the middle of the bridge, the bridge suddenly vibrated strongly and eventually broke and collapsed, causing many soldiers and citizens to fall into the water and lose their lives. After investigation, the culprit responsible for this tragedy was resonance!

Because when the brigade soldiers walked in unison, a frequency produced was exactly the same as the natural frequency of the bridge, which strengthened the bridge's vibration. When its amplitude reached its maximum limit until it exceeded the pressure resistance of the bridge, the bridge broke. Similar incidents also occurred in Russia and the United States.

Scientific experiment

American inventor Tesla: With a single resonator, the earth can be split into two! He came to Wall Street, climbed up an unfinished steel structure building, took a small object from his coat pocket, clamped it to one of the steel beams, and then pressed a small button on it. After a few minutes, you can feel the steel beam trembling. Slowly, the intensity of the tremor began to increase. Extend to the entire building. Finally, the entire steel structure began to creak and shook. The panicked steel frame workers thought that there was a problem with the building, or even an earthquake, so they hurriedly fled from the elevated to the ground. Seeing the trouble getting worse, he felt that the prank should end, so he took the small item back, and then slipped away through an underground passage quietly, leaving behind the shocked and inexplicable workers on the construction site.

A "small item" is a resonator. It is foreseeable that if he left this small item on for another ten minutes, the building would crash to the ground. The power of this resonator is mainly that it can emit waves of various frequencies. When these waves of different frequencies act on different objects, they can generate a resonance wave. When this resonance wave reaches a certain level, it can be Cause the object to be destroyed.

natural disaster

Also due to the power of resonance, huge glaciers can be cracked by the "gentle" ocean waves. Even the huge waves up to hundreds of meters that often appear in Liduja Bay, Alaska, are due to resonance playing a great role in "fueling the flames." Because resonance is so powerful that it "dominates" in this bay, many sailors "respect" and stay away from this bay.

Earthquakes that have caused heavy casualties and property damage to humans also include resonant "demons of buildings": when a certain plate in the crust fractures, the wave frequency generated is transmitted to the ground and strongly resonates with the building. , So, it caused the tragedy of house destruction and death.

There is also a constant sound of a certain frequency that will break the glass.

Sound or vibration of a certain frequency can cause the resonance of the snow on the top of the mountain, causing a big avalanche in an instant.

The destructive nature of resonance is terrible. Today, humans have more diverse and advanced methods to deal with the harm of resonance.

For example, in places with high requirements for sound insulation, it is often used to install some sponges, plastic foams or curtains, so that when the sound frequency hits these soft objects, it cannot resonate with them, but is absorbed by them. .

To deal with noise, people invented a muffler, which is composed of an orifice plate with many small holes and a cavity. When the frequency of the transmitted noise is the same as the natural frequency of the muffler, it will be generated by the air column in the small hole. Violent resonance. In this way, a considerable part of the noise can be "swallowed" at resonance, and it can also be converted into heat for use.

In order to reduce the harm of resonance to buildings and bridges, a device that can quickly attenuate the generated vibration when subjected to an impact, and increase damping, is also born, that is, a damper.

Resonance is a very common natural phenomenon. It can be observed in almost all branches of physics and many interdisciplinary subjects, as well as in various fields of engineering technology. It has applications (radio stations, construction industry, microwave technology, music fields, Medical and scientific research fields).