在我们一般人看来,大地是挺安稳的。然而现代仪器的观测,证明从地球的表层到里层都在连续不断地运动着;由于这些运动所引起的振动,传播出来,就是地震波。振动现象是我们生活中经常可以遇到的。弹性体受到外力作用,它的质点就会从原来位置沿直线或圆弧作往复运动,这就是振动。弹性体具有一个很有趣的特性,就是在弹性体的任何一部分发生振动的时候,振动立刻就会向各个方面传播。如果有人在桌子一端拍击,你把 In our eyes, the earth is very stable. However, the observations of modern instruments have proved that they are continuously moving from the surface to the inner layers of the Earth. The vibrations caused by these movements are transmitted as seismic waves. The phenomenon of vibration is often encountered in our lives. The elastic body is subjected to an external force, and its mass point will reciprocate along a straight line or an arc from its original position. This is vibration. An interesting feature of elastomers is that when vibration occurs in any part of the elastomer, vibrations will be transmitted immediately to all parties. If someone slaps at the end of the table, you put