It is a large destructive earthquake geological disasters. Eastern Han Dynasty in our country, there is a scholar named Zhang Heng invented a called "seismograph" instrument - The instrument is said to be able to determine the orientation of the earthquake (no phone because the ancient and remote sensing satellites, so it looks like this instrument for timely relief is still very useful), then the Zhang Heng seismograph is it really effective?
We can analyze this thing up from the mechanical point of view.
We know that the instrument Zhang Heng era of mechanical equipment, electronic equipment was not yet what sensors, analog circuits and digital circuits are not only some were bronze. So Zhang Heng in 134 AD years ago to do the core components of the seismograph is a cylindrical rollers bronze - for the record "Han" is vague, we can roughly judge the possibility of three different sub-cylinder can exist, namely :
a: free upper and lower ends fixed
b: free lower end, the upper end of the fixed
c: upper and lower ends are free, not fixed
Before the earthquake, which is the root of cylindrical rollers will move towards a certain direction dump, hit the dragon spit in the direction of the beads, was under the frog catch.
Therefore, from the mechanics point of view, this cylindrical rollers at the time of an earthquake dumping, which is the use of so-called "resonance" of physics.
Resonance mean: the natural frequency of the copper pillars (any solid has a natural frequency, all bridge also has the inherent frequency, the army on the bridge marching frequency if the bridge natural frequency of the same, it will resonate) launch and before an earthquake infrasound (below 20 Hz a frequency sound waves) frequency is very, very close, so copper pillar infrasound waves from the seismic energy is absorbed, leading to the occurrence of resonance amplitude increasing copper pillar, it will soon collapse.
So, the question is, which direction should the copper pillars collapsed?
According to the China Earthquake Networks collapse direction Feng Rui, who tests the copper pillar is random, not necessarily in that direction will collapse the earthquake.
Thus, it can be said Zhang Heng "seismograph" is the use of "resonance" principle to work, it is worthy of recognition (because before times the speed of sound before the earthquake quickly, in a longitudinal wave and shear wave seismic pass over, infrasonic step Arrive early site of the incident, so this has a certain role seismograph earthquake prediction), but this "seismograph" is unable to determine the orientation of the earthquake.
Living with resonance to explain the phenomenon, from the Han Dynasty to the Jin Dynasty, it has become one of the mainstream academic thought at the time. Jin Dynasty scholar Zhang once in his book "Natural History" in the explanation of a phenomenon: some people at home at the time of copper Lianpan morning evening will somehow shook himself, buzzing sound, Zhang explained that this because the natural frequency of the palace in the morning and evening Lianpan copper bell twice the frequency of the sound is consistent, resonance occurs.
Therefore, Zhang Heng seismograph, can also be explained Zhang theory.
Because Zhang Heng seismograph already lost, seismograph model we can now see are descendants according to historical records recovery. Which is now the most common of the old model, the 1951, Wang Duo model has been demonstrated in recent years from the appearance that the principles are wrong. Another model by the China Seismological Bureau Feng Rui (2005) proposed that "all columns" is hanging pendulum swing underneath a small ball, the ball in the "m" shaped chute Interchange (ie, "Han Zhang Heng Chuan "and he said" off "), when the earthquake," column are "struck the ball, the ball Longkou firing control organs, so Longkou open. In addition, Feng Rui model also toad by the bottle for bottle body back to the body and serve as the instrument feet. The model tested by simulation, cylindrical rollers above-mentioned second case of high sensitivity, at the time of the earthquake can make a good response, but can not perceive the orientation of the earthquake, the test results and historical records (Zhang Heng seismograph forecast Longxi earthquake this thing) pieces fit.
Therefore, to predict earthquakes orientation, but also need more advanced equipment, which is the era of the Eastern Han Zhang Heng, it is an impossible task.
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