自然界中有各种各样的声音。优美动听的音乐,可以使你心旷神怡,精神焕发;而拖拉机起动时的刺耳声音,却吵得你心烦意乱,不得安宁。我们把后一种声音称为噪声,显然这是人们生活中不需要的一种有害声音。噪声是怎样产生的呢?声音都起源于振动,固体、气体和液体都会因振动而发声,噪声也不例外。一台运转着的拖拉机,它的各个部分都在剧烈地抖动,不仅如此,从排气管排出的废气还会使空气振 There are all kinds of sounds in nature. Beautiful and pleasant music, can make you feel good, full of energy; and harsh sound when the tractor starts, but noisy you upset, no peace. We call the latter kind of noise, apparently a harmful voice that people do not need. How does the noise come about? The sounds all originate from the vibration, the solid, the gas and the liquid all make the sound because of the vibration, the noise is no exception. A working tractor, its parts are shaking vigorously, not only that, from the exhaust pipe exhaust will make air vibration