spool outward travel 滑阀向外行程
outward travel 向外行程
travel outward
向外旅行
以上为机器翻译结果，长、整句建议使用 人工翻译 。
Sound waves travel outward like balloons expanding around their source. The sound's power is distributed on the surface of the wave which increases with the square of the distance from its source.
声波的扩散就好比气球的膨胀，声波从声源向四周扩散，声音的能量也随着声波四散开来。
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