The world is filled with many interesting sounds. Some are unpleasant to our ears while others are very pleasant to hear. In a single day you probably hear hundreds of different sounds. All sounds are different. Some may be loud. Some are high; others are low. Some sounds are useful.
Without sound we cannot talk or listen to one another. The ringing of the alarm clock wakes people up. The hooting of a car warns people of danger.
Some sounds are harmful. When planes fly low over the land, the very loud sounds can damage the houses. Very loud sounds can even make people deaf.
We know sound travel about one kilometer in three seconds. In a thunder storm you see the lightning first then hear the thunder. This is because light travels much faster than sound.
Next time you see lightning; the number of seconds before you hear the thunder. Divide this number of seconds before you hear thunder. Divide this number by 3. This will tell you how many kilometers away the thunder storm is.
这个世界充满了许多有趣的声音。对于我们的耳朵而言，有些是不舒适的，有些则是悦耳动听的。在一天之内你可能听到数以百计的不同声音。所有的声音是不同的。有些可能是响亮的。有些高的，有些低的。有些声音是有用的。
没有声音，我们彼此不能听说。闹钟铃声唤醒人们。汽车的啼声警示处于危险状况的人们。
有些声音是有害的。当飞机在陆地上方低空飞行，巨大的声音可能会损坏房屋。巨大的声音，甚至可以使人耳聋。
我们知道， 3秒钟里声音传播约1公里。在雷雨天你先看到闪电，然后再听到雷声。这是因为光的速度比声音的速度传播得快的多。
下次看到闪电，在听到雷声之前，你计算闪电秒数。均分听到雷声之前的秒数，即除以3。这会告诉你多少公里外有雷雨风暴。
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