The phenomenon of resonance is observed in mechanical oscillatory systems that are periodically exposed to external forces. These forces transfer a certain energy to the oscillatory system, which turns into the energy of motion, i.e. the system oscillates and the amplitude of oscillations increases and becomes maximum when an external force acts on the oscillatory system with the same frequency as the oscillation frequency of the system itself - this is RESONANCE.

Suspension bridges have a number of undeniable advantages compared to other types of bridge designs. However, it has long been noted that suspension bridges are very unreliable in strong winds. One of the largest disasters in the history of bridge construction was the collapse of the bridge over the Tacoma River (USA) on November 7, 1940. The construction of this bridge was completed in the summer of 1940. The span, the third longest in the world, was 854m long. Much traffic was not expected and the bridge was built very narrow - 11.9 m wide. The roadway was designed for 2 rows of cars. The road surface was suspended on two steel ropes with a sag of 70.7 m.
Immediately after construction, the bridge was found to be highly sensitive to the action of wind; the amplitudes (ranges) of vibrations of the bridge reached 1.5 m. Several attempts were made to eliminate these large vibrations by introducing additional connections and installing hydraulic dampers (shock absorbers) on the pylons; This is the name given to the pillars that support the main (bearing) cables in suspension bridges. But this did not prevent the disaster.
Starting from 8 a.m. on November 7, not very strong vertical multinodal (in the form of several waves) bending vibrations with a frequency of 0.8 Hz were observed. It is noteworthy that the wind did not have a very high speed, about 17 m/s, whereas before this there were cases when the bridge withstood stronger winds. At about 10 a.m., the wind speed increased slightly (up to 18.7 m/s), and single-node (in the form of a single wave) flexural-torsional oscillations with a significantly lower frequency (0.2 Hz) and very large amplitudes were established. When the spin reached its maximum, the roadway tilted toward the horizon at an angle of 45°. The sharp change in the oscillation frequency occurred, apparently, as a result of the breakage of some important connections in the structure. The bridge withstood these vibrations for about an hour, after which a large section of the roadway broke off and fell into the water. The entire process was filmed, which provided valuable material for research into the causes of the collapse.
The disaster has attracted enormous research attention. Just two weeks after the fact, the famous mechanic T. von Karman gave an explanation of the causes of the disaster and even indicated the wind speed at which this could happen. The destruction occurred at a wind speed of the order of 18 - 19 m/s, and T. von Karman calculated 22.2 m/s. So even this can be called a mechanic's success.
What conclusions did the mechanics draw from this? Another bridge has now been built across the Tacoma River. Its width has been increased by more than 1.5 times and is 18 m, and the cross-section of the roadway has also been changed. In addition, solid beams are replaced with through trusses, which significantly reduces the force of wind pressure. Modern suspension bridges are lightweight structures suspended by steel cables called cable stays. They can withstand high winds and other loads and have been functioning normally for many years. It is known that such catastrophes as happened with the Tacoma Bridge cannot happen here. The mechanics were able to understand what could happen and how to prevent it.
Resonance can occur when a large mass, for example, a soldier in formation, must cross a bridge while marking a step; at the same time, the command sounds to stop marching, people cross the bridge like ordinary pedestrians... Machines with rotating parts are installed on massive foundations. so that when the machine swings (which cannot be avoided), resonance does not occur at the foundation and it does not collapse.
The phenomenon of resonance is the basis of radiotelephone communications and telecommunications.

Everywhere and every day we are accompanied by oscillatory systems in our lives.
The first impression in life is a swing. In this by no means simplest example, one can observe the dependence of the period of oscillation on the weight of the person swinging, as well as the problem of the movement of the swing being in phase with the external swinging force. Next, there is an acquaintance with musical instruments, one way or another using various kinds of oscillatory systems to produce musical sounds. Well, and in the end, all the electronics that completely embrace us, the main and indispensable unit of which is a quartz resonator - a refined oscillatory system, so to speak.
And at the same time, do we understand so much about this...
The clearest definition of an oscillatory system was given by Lord Kelvin when he discovered the electric L-C oscillatory circuit in 1878. Having discovered that when an impact is applied to an oscillatory circuit, a sinusoidal (harmonic) damping process occurs, Kelvin stated that this is proof that a new, previously unknown oscillatory system is taking place.
Thus, we can formulate that an oscillatory system is a device that has a mechanism for converting impact into a harmonic damping process.
But what is interesting is that we cannot apply this definition to all known and used oscillatory systems. This happens because for these devices, which are definitely oscillatory systems (according to Kelvin’s definition), the mechanism itself for converting the shock into a sinusoid is not always known.
As for various types of pendulums, springs and oscillatory circuits, the mechanisms of their oscillation have been studied and discussed. However, there are oscillatory systems whose mechanism is unknown, despite their very wide application. Thus, until recently it remained unknown how, say, quartz resonators play the role of an oscillatory system.
The quartz resonator effect was discovered back in 1917, but for some reason they were embarrassed to admit its incomprehensibility. Due to this shyness, a model of a quartz resonator was proposed in the form of its equivalent to a certain combination of several virtual capacitors and inductors. For some reason this kind of modeling is called a scientific description of quartz resonators, it’s all called theory, and this kind of scientific and educational literature exists apparently and invisibly.
It is clear that there are no virtual or real capacitors in quartz resonators, and all this scientific waste paper has nothing to do with these resonators. The fact is that in practice the frequency of a quartz resonator f 0 is determined by the thickness of the quartz plate h, and in its manufacture the following empirical formula is used:

f 0 = k / h, where (1)

k - technological coefficient.
So, in all the existing literature on quartz resonators, we will not find any mention of this empirical relationship, or any information at all about the connection between the natural frequency of the resonator and the dimensions of the plate.
60 years after the discovery of the properties of quartz plates, in 1977, it was discovered that not only quartz plates, but also objects from the vast majority of solid media (metals and alloys, glass, ceramics, rocks) are resonators. It turned out that the number of natural frequencies of these resonators is equal to the number of their sizes. So, a solid ball, say, made of glass, has only one size - diameter d, and, accordingly, one natural frequency f 0 , the connection between which, as it turns out, is determined by relation (1). A plate having a thickness h and sizes a And b, has three natural frequencies, each of which is related to the corresponding size by relation (1).
The presence of resonant properties of the objects listed above is revealed very simply, and even in several ways. In mine conditions, in the case of layered rocks, the simplest method is to press an elastic vibration field sensor (seismic receiver) to the object under study (roof rocks) and apply a short blow to the roof surface. The shock response will appear as a decaying harmonic signal. This method is not suitable in laboratory conditions because it is very difficult to obtain the required impact parameters for small samples. In the laboratory, it turned out to be easier to use ultrasonic testing of the sample.
As it turned out, the resonant properties of a quartz resonator are not something unique and depend on the presence of the piezoelectric effect. The presence of the piezoelectric effect only simplifies the indication and use of this property. Thus, when studying the resonant properties of a piezoceramic disk, during the experiment it can be heated to a temperature exceeding the Curie point, at which the piezoelectric effect disappears, and its resonant properties will not change in any way.
However, if the scientists who studied quartz resonators managed to avoid searching for the physics of their resonant properties, then I had to take it seriously. The fact is that, despite the actually existing resonant manifestations, based on general considerations, a plate made of a homogeneous material should not exhibit resonant properties. Such a plate should not have a mechanism for converting the impact into a harmonic signal.
It cannot be said that this point of view is wrong, because there are materials from which objects are not resonators. Indeed, in materials such as plexiglass (plexiglass) and some others, this mechanism is absent. Plexiglas objects are not resonators. When impacted on a plexiglass plate, the reaction takes the form of a sequence of damped short pulses. That is, it fully complies with the provisions of generally accepted acoustics of solid media.
At the same time, as it turned out (in 1977), rock layers exhibit resonant properties, and using relation (1) it turned out to be possible without drilling (!) to determine the structure of the rock mass. Well, it is clear that it is very difficult to use a physical effect even though it is not difficult to prove the impossibility of its existence. In addition, the use of this effect in mines made it possible to create a method for predicting the collapse of roof rocks - a phenomenon that accounts for 50% of the injuries to miners throughout the world. But it was completely impossible to introduce into practice a technique based on such a dubious physical effect.
It took 4 years to find the difference between plexiglass and those materials from which objects are resonators. And somewhere in 1981, it was discovered that there is a difference, and it concerns the acoustic properties of the border zones of the vast majority of solid media.
It turned out that the acoustic properties of near-surface zones of media, objects from which exhibit the properties of resonators, are such that the speed of propagation of the front V fr during normal sounding it is not constant, and decreases as the front approaches the surface.
Figure 1 shows the case of normal sounding of a resonator plate 1 thick h. Addiction V fr (x), as well as minimum and maximum values V fr and zone sizes Δ h obtained from measurements made on many plates of the same material but having different thicknesses. Average speed Vfr.mid- this is the value that is obtained when determining the speed at the moment of the first entry.
In similar studies of plexiglass plates, the speed Vfr.mid when changing plate thickness h remains constant, from which we can conclude that in plexiglass (non-resonator plate) the zones Δh are missing.
When emitted by an emitter disk 1 harmonic signal, at the natural frequency of the sounded resonator plate f 0, that is, at resonance, emf. on the destination disk 3 disappears but appears on the destination disc 4 . This effect is called acoustic resonance absorption (ARA).

Rice. 1

Piezoceramic disk emitter 2 , sound plate 1 and piezoceramic receiver disks 3 And 4 are in liquid (water or oil).
Thus, at resonance there is a reorientation of the primary field emitted by the piezoelectric transducer 1 , in the orthogonal direction. The field rotation in the orthogonal direction occurs in the presence of near-surface zones Δ h.
Relationship between the presence of zones Δ h and rotating the field in the orthogonal direction is quite simple. The fact is that the speed of movement of any object or the speed of propagation of any process cannot change without external influence. Therefore, in fact, in the zone Δ h it is not the speed of front propagation that changes V fr, and her x -component, which is possible only if there is an occurrence y -component. In other words, the vector remains constant in magnitude, but in the zones Δ h the vector rotates V fr.
That is, it turns out that when a resonator layer is impacted, its surfaces become emitters of its own frequency f 0, and with a harmonic emitter, the resonator layer becomes sound opaque at resonance. But in both cases, under any influence, a field of elastic vibrations propagates along the resonator layer with a frequency f 0 .
Acoustic isolation of a resonator layer at its natural frequency from adjacent objects has been used for a very long time. Thus, it was noticed that if you put your ear to the ground, you can hear cavalry over enormous distances. In fact, it is not the cavalry that is heard, but the natural vibrations of the rock resonator layer, excited by the horse’s hooves. The very weak attenuation of the field propagating along the resonator layer is precisely a consequence of its acoustic isolation from the adjacent rocks.
When a rock mass is impacted during seismic exploration, the resulting field of elastic vibrations propagates along the rock bedding. This contradicts the fundamentals of seismic exploration, which states that the field generated by an impact spreads out in all directions.
This is a very serious moment for understanding the operating principle of seismic exploration. It turns out that the signals received on seismograms come not from below, not from the depths, but from the side, since they propagate exclusively ALONG the bedding.
In the spectral analysis of seismic signals, it turned out that relation (1) is satisfied when the coefficient is k in the numerator equal to 2500m/s. In this case, the error in determining the thickness of the rock layer does not exceed 10%.
It must be assumed that a process oriented in the direction y with directed radiation in the direction x , is transverse. And thus, it can be argued that the own oscillatory process is formed by transverse waves, and the coefficient k is nothing more than the speed of transverse waves Vsh.
The discovery of essentially new, previously unknown oscillatory systems requires a restructuring of thinking. When at one time it was discovered that the Earth is a sphere, the realization of this, as well as the transition from the geocentric to the heliocentric system, required a restructuring of the consciousness of the inhabitants of the Earth. However, this restructuring took several centuries, since this new information did not require any special changes in the algorithms of living conditions. Now the situation is somewhat different.
Due to the fact that our planet consists largely of rock layers, it turns out that in general it is a collection of oscillatory systems. This means that any impact on the Earth’s surface should cause a reaction in the form of a set of harmonic damped processes. If the impact is vibrational, then resonance phenomena become possible.
When considering resonant phenomena, there is a need to take into account a parameter characteristic of oscillatory systems - quality factor Q. The very definition of quality factor contains information about the colossal destructive potential of resonance. The quality factor Q shows how many times the vibration amplitude increases in the event of resonance.
Real values ​​of Q for oscillatory systems implemented by geological structures located in the earth's thickness can reach several hundred. And if in the zone of such a high-quality oscillatory system there is an object that exerts a vibration (dynamic) effect on the ground, then the amplitude of the vibration of this object will increase exactly that many times.
However, the increase in vibration magnitude has certain limitations. These limitations are determined by the fact that at a certain vibration amplitude, elastic deformations are exceeded and destruction occurs. The soil that is exposed to vibration can collapse, and this is manifested by instantaneous, explosive subsidence, with the formation of a crater. When reinforcing the soil with various kinds of reinforced concrete structures (for example, a reinforced concrete dam for a hydroelectric power station), the studs on which the generator is attached to the dam may fail and break.
At small values ​​of Q (say, up to 10), resonance manifests itself as increased vibration. This is unpleasant for the operating personnel; it leads to the formation of various kinds of backlash and imbalance in the operating mechanism, but such a low-Q resonance will not cause crushing, instant destruction.
If Q is significantly greater than the limiting value at which the vibration amplitude causes inevitable destruction, resonance can only exist for a short time. So, let’s say that with the standard vibration frequency of the dynamo 50 Hz, directly under this installation lies a geological structure that has a natural frequency of, say, 25 Hz with a quality factor Q = 200. Then, during the entire period of normal operation, vibration will be within normal limits. However, suppose that for some reason the machine needs to be stopped, and then, during the process of stopping, for some time, its rotation frequency will be close to the resonant one, 25 Hz. In the resonance zone, a smooth increase in the vibration amplitude will begin. And here the question is how quickly the rotor speed passes the resonance zone, and whether the vibration amplitude has time to increase to a destructive value.
It is easy to notice that here, as an example, the situation that developed at the Sayano-Shushenskaya HPP was considered. There, the vibration of hydraulic units in normal operating mode increased to unacceptable values. And when the decision was made to stop, the speed began to decrease very slowly. As a result, when passing through the high-Q resonance zone, the vibration amplitude managed to increase so much that the studs securing the hydraulic unit could not stand it. And, by the way, the recorders of the hydraulic unit showed an increase in vibration by 600 times.
A characteristic sign and harbinger of resonant destruction is an increase in vibration.
The first reliable evidence of the presence of such a precursor occurred during the Chernobyl accident. There, after all, it all started with a change in the reactor mode and, accordingly, the rotation speed of the units. At the same time, a vibration began, the amplitude of which began to quickly increase, reaching such a level that people began to leave this area in panic. The vibration was interrupted by a seismic shock (explosive destruction of the soil), noted by seismologists. And only half a minute after this, the destruction of the reactor occurred.
Subsequently, information appeared that this harbinger occurs during the destruction of various types of pumping stations. In the same way, when the vibration frequency of the compressor changes, the vibration amplitude suddenly begins to increase, ending with the equipment sinking into the ground. The cause of such an event is usually cited as either a terrorist attack or poor-quality piles on which the station stands.
Railway accidents often occur when, for no apparent reason, a train breaks into two parts, when suddenly, suddenly, an embankment collapses explosively, forming a depression, and instantly destroyed sleepers and pieces of rails fall into this funnel. It is at this moment of track destruction that the train breaks. However, in the car, which turns out to be the last one to pass through this zone, there is a strong vibration, which ends with the instant destruction of the embankment.
On August 13, 2007, such an accident occurred in the Novgorod region with train N166 Moscow - St. Petersburg. Eyewitnesses later described what happened: “...at first the train began to shake, followed by a bang. The guides, who have been working on this route for many years, later admitted that they began to say goodbye to life, since this was the first time in their memory that this had happened.” The key point is that witnesses felt a strong vibration before the impact.
On March 3, 2009, a six-story archive building suddenly collapsed in Cologne. As reported by Reuters, there was a rumble and strong vibration before the collapse. “The table I was sitting at shook and I thought someone had accidentally kicked it,” said one visitor to the archive. - After everything started to shake like during an earthquake" The house turned into a pile of bricks in just seconds. A police spokesman told reporters that "it looked like an explosion" with bricks, boards and pieces of cement scattered across the pavement in a radius of up to 70 meters. A metro line runs under the archive building, the tunnel of which also collapsed. The source of the vibration, as it turned out, was in the subway tunnel. This source was a drilling rig operating there.
The physics of resonant damage is discussed in detail in the works. Here it seems necessary to pose the following question. It is well known that an increase in the amplitude of vibration, ending in an explosion-like destruction, is uniquely associated with resonant phenomena. So why do we never hear the word “resonance” when investigating disasters that had such a precursor? The reason turned out to be purely psychological. According to the established opinion, there are NO oscillatory systems in the earth's thickness. And if there are no oscillatory systems, then there can be no talk of resonance.
If we nevertheless assume the assumption of resonance, then the question of the oscillatory system is inevitable. Because without an oscillatory system there can be no resonance.
Further, if we assume that the earth's strata really represent a collection of oscillatory systems, then this undermines the foundations of seismic exploration. After all, consideration of seismic exploration is possible only within the framework of its generally accepted model, according to which the earth's strata is a collection of reflective boundaries.
It doesn't matter whether seismic exploration provides information or not, because it is a colossal, multi-billion dollar business that cannot be touched. A business built on falsifications, but so huge that seismic exploration no longer needs anyone to confirm it.
Now there are probably no functioning scientists who would not know that it is a proven fact that our planet is a collection of oscillatory systems. But now their main task is to pretend that they don’t know this. Any discovery to one degree or another negates the previous level of knowledge. Yes, indeed, if this point of view were mastered and accepted, the number of man-made disasters would decline. But alas, scientists don’t need this. For them, the main thing is to survive until the end of their lives at the level they have achieved, and so that no one crosses out the level of knowledge at which they reached their heights. And this certainly outweighs in importance for them all those catastrophes that could have been prevented.

LITERATURE

1. Glikman A.G. The effect of acoustic resonance absorption (ARA) as the basis of a new paradigm for the field theory of elastic oscillations.
2. Certificate from Northern Express conductors www.newsru.com/russia/14aug2007/train.html
3. Evidence of the destruction of the archive in Cologne www.gazeta.ru/social/2009/03/04/2952320.shtml
4. Glikman A.G. Vibration and resonance phenomena in our lives (what happened at the Sayano-Shushenskaya hydroelectric station)
5. Glikman A.G. Planet Earth as a set of oscillatory systems and man-made and natural earthquakes as consequences of this

Before you begin to get acquainted with the phenomena of resonance, you should study the physical terms associated with it. There are not many of them, so it will not be difficult to remember and understand their meaning. So, first things first.

What is the amplitude and frequency of movement?

Imagine an ordinary yard where a child sits on a swing and waves his legs to swing. At the moment when he manages to swing the swing and it reaches from one side to the other, the amplitude and frequency of the movement can be calculated.

Amplitude is the greatest length of deviation from the point where the body was in the equilibrium position. If we take our example of a swing, then the amplitude can be considered the highest point to which the child swings.

And frequency is the number of oscillations or oscillatory movements per unit time. Frequency is measured in Hertz (1 Hz = 1 cycle per second). Let's return to our swing: if a child passes only half the entire length of the swing in 1 second, then its frequency will be equal to 0.5 Hz.

How is frequency related to the phenomenon of resonance?

We have already found out that frequency characterizes the number of vibrations of an object in one second. Imagine now that an adult helps a weakly swinging child to swing, pushing the swing over and over again. Moreover, these shocks also have their own frequency, which will increase or decrease the swing amplitude of the “swing-child” system.

Let's say an adult pushes a swing while it is moving towards him, in this case the frequency will not increase the amplitude of the movement. That is, an external force (in this case, pushes) will not increase the oscillation of the system.

If the frequency with which an adult swings a child is numerically equal to the swing frequency itself, resonance may occur. In other words, an example of resonance is the coincidence of the frequency of the system itself with the frequency of forced oscillations. It is logical to imagine that frequency and resonance are interrelated.

Where can you see an example of resonance?

It is important to understand that examples of resonance are found in almost all areas of physics, from sound waves to electricity. The meaning of resonance is that when the frequency of the driving force is equal to the natural frequency of the system, then at that moment it reaches its highest value.

The following example of resonance will give insight. Let's say you are walking on a thin board thrown across a river. When the frequency of your steps coincides with the frequency or period of the entire system (board-person), the board begins to oscillate strongly (bend up and down). If you continue to move in the same steps, the resonance will cause a strong vibration amplitude of the board, which goes beyond the permissible value of the system and this will ultimately lead to inevitable failure of the bridge.

There are also areas of physics where it is possible to use such a phenomenon as useful resonance. The examples may surprise you, because we usually use it intuitively, without even realizing the scientific side of the issue. So, for example, we use resonance when we try to pull a car out of a hole. Remember, it is easiest to achieve results only when you push the car as it moves forward. This example of resonance increases the range of motion, thereby helping to pull the car.

Examples of harmful resonance

It is difficult to say which resonance is more common in our lives: good or harmful to us. History knows a considerable number of terrifying consequences of the resonance phenomenon. Here are the most famous events where an example of resonance can be observed.

1. In France, in the city of Angers, in 1750, a detachment of soldiers walked in step across a chain bridge. When the frequency of their steps coincided with the frequency of the bridge, the range of vibrations (amplitude) increased sharply. There was a resonance, and the chains broke, and the bridge collapsed into the river.
2. There have been cases when in villages a house was destroyed due to a truck driving along the main road.

As you can see, resonance can have very dangerous consequences, which is why engineers should carefully study the properties of construction objects and correctly calculate their vibration frequencies.

Beneficial Resonance

The resonance is not limited to dire consequences. By carefully studying the world around us, one can observe many good and beneficial results of resonance for humans. Here is one striking example of resonance that allows people to receive aesthetic pleasure.

The design of many musical instruments operates on the principle of resonance. Let's take a violin: the body and the string form a single oscillatory system, inside of which there is a pin. It is through it that vibration frequencies are transmitted from the upper deck to the lower one. When the luthier moves the bow along the string, the latter, like an arrow, overcomes the friction of the rosin surface and flies in the opposite direction (begins to move in the opposite area). A resonance occurs, which is transmitted to the housing. And inside it there are special holes - f-holes, through which the resonance is brought out. This is how it is controlled in many stringed instruments (guitar, harp, cello, etc.).

The Tacoma Narrows Bridge (Tacoma Bridge) belongs to the category of hanging bridge structures. Located in Washington State, United States of America. It is laid through the Tacoma Narrows, which, in turn, is part of Puget South Sound.

History of creation

Initially it was built according to the design of Leon-Solomon Moiseev, a native of Russia. He is known as a design engineer, bridge builder, and an active participant in public life. The Tacoma Bridge opened to traffic in July 1940. Already during its construction, the builders noticed vibrations and swaying of the bridge road surface when the wind increased. This was due to the insufficiently high stiffening beam. In everyday life, the bridge began to be called “Galloping Gertie”.

Bridge characteristics

At the time the Tacoma Bridge was built, it was a remarkable structure. It was a hanging (cable-stayed) three-span structure. Its total length was 1810 meters. And the length of the central suspended span is 854 meters. The bridge was about 12 meters wide. The main supporting cables had a diameter of 438 millimeters. The stiffening beam reached a height of 2.44 meters, which was later recognized as a miscalculation. The bridge structure was supported by steel pylons standing on concrete supports (bulls).

Crash

On November 7, 1940, when the operation period was only four months, the destruction of the Tacoma Bridge occurred. On this day, the wind speed reached 65 km/h. Given that there was minimal traffic on the bridge that day, this made it possible to avoid casualties.

The very fact of destruction in dynamics was captured on film. This made it possible to subsequently carefully study and investigate this process. The newsreels and photos of the Tacoma Narrows Bridge in the process of its destruction are indeed very impressive.

The film was used to create the internationally acclaimed documentary The Tacoma Narrows Bridge Collapse.

Causes of destruction

Based on the results of research and the study of documentary materials, it was established that the main factor leading to the accident was extreme dynamic torsional vibrations caused by strong winds. It was found that the Tacoma Bridge project was calculated and designed taking into account only statistical and wind loads. However, the possible impact of aerodynamic factors on its design has not been studied.

The vibration of the bridge deck arose due to It began to intensify due to the vertical vibration of the cables. The weakening of the cable on one side of the bridge and the tension on the other gave rise to torsional phenomena, led to the tilt of the pylons and, as a consequence, to the breakage of the suspensions of the central span. The bridge turned out to be structurally too flexible, with little resistance to absorbing dynamic forces.

Filming recorded that the bridge began to sway when the wind speed was about 19 meters per second. Although in the project its resistance to winds was calculated based on 50 meters per second.

conclusions

The destruction of the Tacoma Bridge forced bridge designers (and others) to begin research in the field of aerodynamics, aerodynamic stability of structures and structures. This has led to a change in thinking about the design of long span bridges.

In theory, the cause began to be designated as the phenomenon of forced mechanical resonance. However, in practice it is believed that the so-called led to it. aeroelastic flutter (torsional vibrations) due to insufficient calculations of wind loads at the design stage.

New bridge

The dismantling of the collapsed structure began immediately after the accident. The pylons and side spans were dismantled. This process lasted until 1943, when construction of a new bridge began. The bases of the pylons, anchor abutments, and some other parts from the old structure were used. The recreated bridge was put into operation in October 1950. At that time it became the third suspension bridge in the world (based on its length of 1822 meters).

In order to impart and reduce loads of an aerodynamic nature, open-type trusses were introduced into its elements. Installed additional stiffeners. It is equipped with expansion joints and vibration damping systems. The bridge could carry up to 60 thousand cars per day.

In 2007, another bridge was built parallel to the existing one. The purpose of the construction is to increase the highway's capacity. Its length is 1645.9 m, and its width is 853.4 m. The height of the pylons is 155.4 meters.

We often hear the word resonance: “public resonance”, “event that caused resonance”, “resonant frequency”. Quite familiar and ordinary phrases. But can you say exactly what resonance is?

If the answer jumped out of your mouth, we are truly proud of you! Well, if the topic “resonance in physics” raises questions, then we advise you to read our article, where we will talk in detail, clearly and briefly about such a phenomenon as resonance.

Before talking about resonance, you need to understand what oscillations are and their frequency.

Oscillations and Frequency

Oscillations are a process of changing the states of a system, repeated over time and occurring around an equilibrium point.

The simplest example of oscillation is riding on a swing. We present it for a reason; this example will be useful to us in understanding the essence of the phenomenon of resonance in the future.

Resonance can only occur where there is vibration. And it doesn’t matter what kind of vibrations they are - electrical voltage fluctuations, sound vibrations, or simply mechanical vibrations.

In the figure below we describe what fluctuations can be.

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Oscillations are characterized by amplitude and frequency. For the swings already mentioned above, the oscillation amplitude is the maximum height to which the swing flies. We can also swing the swing slowly or quickly. Depending on this, the oscillation frequency will change.

Oscillation frequency (measured in Hertz) is the number of oscillations per unit time. 1 Hertz is one oscillation per second.

When we swing a swing, periodically rocking the system with a certain force (in this case, the swing is an oscillatory system), it performs forced oscillations. An increase in the amplitude of oscillations can be achieved if this system is influenced in a certain way.

By pushing the swing at a certain moment and with a certain periodicity, you can swing it quite strongly, using very little effort. This will be a resonance: the frequency of our influences coincides with the frequency of oscillations of the swing and the amplitude of the oscillations increases.

The essence of the phenomenon of resonance

Resonance in physics is a frequency-selective response of an oscillatory system to a periodic external influence, which manifests itself in a sharp increase in the amplitude of stationary oscillations when the frequency of the external influence coincides with certain values ​​characteristic of a given system.

The essence of the phenomenon of resonance in physics is that the amplitude of vibrations increases sharply when the frequency of influence on the system coincides with the natural frequency of the system.

Examples of resonance

The phenomenon of resonance is observed in a variety of physical processes. For example, sound resonance. Let's take a guitar. The sound of the guitar strings itself will be quiet and almost inaudible. However, there is a reason that the strings are installed above the body - the resonator. Once inside the body, the sound from the vibrations of the string intensifies, and the one who holds the guitar can feel how it begins to slightly “shake” and vibrate from the blows on the strings. In other words, resonate.

Another example of observing resonance that we encounter is circles on water. If you throw two stones into the water, the passing waves from them will meet and increase.

The action of a microwave oven is also based on resonance. In this case, resonance occurs in water molecules that absorb microwave radiation (2.450 GHz). As a result, the molecules resonate, vibrate more strongly, and the temperature of the food rises.

Resonance can be both beneficial and harmful. And reading the article, as well as the help of our student service in difficult educational situations, will only bring you benefit. If, while completing your coursework, you need to understand the physics of magnetic resonance, you can safely contact our company for quick and qualified help.

Finally, we suggest watching a video on the topic “resonance” and making sure that science can be exciting and interesting. Our service will help with any work: from an essay on “The Internet and Cybercrime” to a coursework on the physics of oscillations or an essay on literature.