Mechanical waves

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  • Publicado : 22 de mayo de 2011
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During our lives, it is almost 100% probable that we will have to be facing a natural disaster due to natural phenomena like seismic waves are. These particular waves are waves of force or energy, and they are formed when rock breaks down in the earth or this breaking down can also take place during an explosion. This is the reason why earthquakes and volcanoes occur in closeplaces. These seismic waves are energy which travels along the air. Frequently, we can see at the news or newspapers stories about tragic accidents due to natural disasters, in this particular case earthquakes created by seismic waves, but in the other hand we can see many successful studies which scientists have carried out with the use of seismic waves. The following text will be addressed to thisissue surrounding us and that leads us to the question: How do mechanical waves affect us?
Earthquakes, caused by seismic waves are studied by seismologists. Seismology is a type of study of the transmission of elastic waves through the earth. These elastic waves are a type of mechanical wave, and the material which they are made of is elastic, and this feature is the one which provides therestoring force of a wave. Seismic waves are measured by a seismograph, and this is an apparatus used to record the different motions of the ground. During an earthquake different types of waves are created at different velocities, and the velocity of a wave depends on the elasticity and the density of the medium on which the wave is travelling through. There are two main types of seismic waves: bodywaves and surface waves. Body waves are the waves which can travel through the earth’s inner layer, they travel through the interior. The effects which this waves cause is that they vary the density and the modulus1 and by varying this two the temperature, the composition and phase varies. Surface waves, are waves which can only move along the surface of the earth, like for example when youproduce circular waves on a ripple tank, a similar action takes place with surface waves.
These waves have two types: primary waves (which is the same as a longitudinal wave), and secondary waves (which is the same as a transverse wave). Primary waves are the fastest type of wave which means that they will be the first to arrive. They also have the ability to move through solids and liquids and themovement which they apply on the earth is pushing and pulling the rocks. At this type of wave, particles move along the wave, they move in the same direction as the wave. These primary waves are the reason why dogs might bark before an earthquake takes place, because animals can hear these waves while humans can only sense them. Secondary waves are the second waves you are able to feel in anearthquake. In difference to the primary waves, they are only able to move through solid rock. This theory helped scientists prove that the earth´s outer core is liquid, since these waves are unable to travel through it. In response to this wave, earth´s particles move up and down or side to side in a perpendicular direction to the direction the wave is travelling.

Example of a primary wave on aspring Example of secondary wave on a spring

Other types of seismic waves which aren’t as general as the two previous are Rayleigh waves and Love waves. Rayleigh waves are waves which travel trough the surface f the earth, like water waves on a ripple tank, but this type of waves have been reconsidered because it is possible that it is an eyeeffect caused by the tremor. The other type of waves are Love waves which are also surface waves which produce a horizontal movement of the ground, this effect is a motion like when you are waving a blanket at the wind for it to dry, you can see a wave motion which is passed from one side of the blanket to the other.
Scientist have made all types of research in order to address this problem,...
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