![]() This is important since it means that the mechanical energy will be following a longer distance (and slower) than the straight road. For the poor atom the movement will thusbe following the direction of the waveform, forth and back. The atoms are pushed in a direction away from the point of origin this creates excess pressure ahead of it (the atoms there resist being pushed), and the atoms are forced back. This in turn creates pressure against the individual atoms. I will get back to longitudinal wave and its estranged cousin the transverse wave.Īs the sound source vibrates it creates vibration in the adjoining media (often the air or water). Mechanical waves within air and water almost to a flaw move as longitudinal waves. There is a difference between waves moving in gases such as air and fluids like water, as in comparison to a solid. But, now I am getting ahead of myself again.īack to the thing with wave propagation and media For recording we use the equipment of a studio or a seismograph. And it is also good to remember that the sound we hear is interpreted by our brains and may not always be as accurate as we tend to believe, and to complicate things even more, our ears are not that great. For sound, may it be a violin or an earthquake rumble, it can be our ear, sensitive but imperfect. To detect a wave we often need specialised equipment. Think Mexican wave: the wave moves, the people remain, sitting still again. The wave passes but the water stays behind. A bird floating on the water will still be in the same place. At sea, after a wave has passed, the surface goes back to how it was before the wave. The net effect of a wave will always be a zero displacement. Once the wave has passed, the vibration stops. They all have in common that they leave nothing behind. Image by Thierry Dugnolle, Wikimedia CommonsĪccording to physics, sound is a vibration that propagates as a mechanical wave, while moving through a medium such as a gas (air), a fluid (water) or a solid (rock). This could be a drum, a stone dropped in a lake, or a small earthquake. Representation of a spherical pressure wave from a point source. ![]() But, as with everything else we need to start at the beginning. ![]() And I really mean everything.īut let us not venture out into quantum physics or plucky string theory instead let us keep to our mutual shared interest of earthquakes and volcanoes. I think this is a pity, because out of the humble little sound wave you can derive everything in the universe. One thing I have noticed is that even though sound waves are all around us all the time, and even though they rule our daily life in the most fundamental ways, very few really know about them and they are rarely if ever studied in schools. A field I have spent 20 years studying and researching. In a way it is not about earthquakes or volcanoes at all, and not even really about sound, instead it is about the strange and wonderful world of waves. This post is about waves, how they happen, how those waves travelling, and how they are seen. This post is based on one we ran in 2014, in the heady days of the months before Holuhraun. Hunga Tonga gave us a reason to delve into the archives, and find what we had written about waves, to learn from ourselves. The whole world rings after a major shake. Like the sounds of Hunga Tonga, their waves traverse the Earth and are detected everywhere. We are more used to associate waves with earthquakes. This volcano made waves – and it was very very good at it. There is a common denominator in these three effects. And all this from a volcano we had never heard about. The ocean wave caused a tsunami across the Pacific, with devastation on nearby islands and damage in Japan and South America. The air pressure wave traveled around the world – and again. The sound wave of Hunga Tonga was heard across the Pacific ocean in Alaska. In January, the world experienced the loudest bang of the century – and that of the previous century as well.
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