17.1 声波
Section outline
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Crack! Crash! Thud! That’s what you’d hear if you were in the forest when this old tree cracked and came crashing down to the ground. But what if there was nobody there to hear the tree fall? Would it still make these sounds? This is an old riddle. To answer the riddle correctly, you need to know the scientific definition of sound.
::如果这棵老树破碎而坠落到地上,你听到的就是这个。但是,如果没有人听到树倒塌的声音呢?它还会发出这些声音吗?这是一个老谜语。要正确解开谜语,你就必须知道声音的科学定义。Defining Sound
::界定声音In science , sound is defined as the transfer of from a vibrating object in waves that travel through matter. Most people commonly use the term sound to mean what they hear when sound waves enter their ears. The tree above generated sound waves when it fell to the ground, so it made sound according to the scientific definition. But the sound wasn’t detected by a person’s ears if there was nobody in the forest. So the answer to the riddle is both yes and no!
::在科学中,声音被定义为在物质穿梭的波浪中从振动物体中传来的声音。 大多数人通常使用这个词来表示当声波进入耳朵时听到的声音。 上面的树在落地时产生了声波,因此根据科学定义发出声音。 但是,如果森林里没有人的话,一个人的耳朵没有检测到声音。 因此谜语的答案是是肯定的,不是!How Sound Waves Begin
::声音波如何开始All sound waves begin with vibrating matter. Look at the first guitar string on the left in the Figure . Plucking the string makes it vibrate. The diagram below the figure shows the wave generated by the vibrating string. The moving string repeatedly pushes against the air particles next to it, which causes the air particles to vibrate. The vibrations spread through the air in all directions away from the guitar string as longitudinal waves. In longitudinal waves, particles of the medium vibrate back and forth parallel to the direction that the waves travel.
::所有声音波都以振动物质开始。 看看图中左侧的第一个吉他字符串。 拨动字符串使它振动。 图表下方的图表显示振动字符串产生的波。 移动字符串反复向旁边的空气颗粒推动, 导致空气颗粒振动。 振动从吉他字符串向外扩散到各个方向, 如长垂直波。 在纵向波中, 中等振动颗粒与波浪移动的方向平行。Q: If there were no air particles to carry the vibrations away from the guitar string, how would sound reach the ear?
::问:如果没有空气微粒能将振动从吉他弦上移开,A: It wouldn’t unless the vibrations were carried by another medium. Sound waves are mechanical waves, so they can travel only though matter and not through empty space.
::答:除非振动是由另一种媒介传播,否则它不会。 声波是机械波,因此它们只能通过物质而不是空地进行移动。What about the sound waves created by other instruments? Why does the same musical note on different instruments, such as a guitar and violin, sound different? Begin your exploration of sound by exploring the different types of sound waves produced by string instruments in the Violin SIM below:
::其它乐器所创造的声波呢?为什么在吉他和小提琴等不同乐器上的音乐音符会不同? 开始探索声音,探索以下Violin SIM的弦乐器产生的不同类型的声波:A pan flute is another example of a musical instrument that depends on the vibration of air particles. Use the simulation below to visualize how the movement of invisible air molecules inside the tubes produces musical notes:
::Pan 长笛是音乐乐器的另一个例子,它取决于空气微粒的振动。 使用下面的模拟来直观地想象在管内无形空气分子的移动如何产生音乐音符:A Ticking Clock
::选中时钟The fact that sound cannot travel through empty space was first demonstrated in the 1600s by a scientist named Robert Boyle. Boyle placed a ticking clock in a sealed glass jar. The clock could be heard ticking through the air and glass of the jar. Then Boyle pumped the air out of the jar. The clock was still ticking, but the ticking sound could no longer be heard. That’s because the sound couldn’t travel away from the clock without air particles to pass the sound energy along.
::1600年代,一个名叫Robert Boyle的科学家首次展示了声音不能穿越空地这一事实。 Boyle把一个时钟放在一个密封的玻璃罐里。 时钟可以从罐子的空气和玻璃中听到。 然后Boyle从罐子上抽出空气。 时钟仍然在滴答,但时钟无法再听到。 这是因为声音不能在没有空气粒子的情况下离开时钟,通过声音能量。Sound Waves and Matter
::音波和音波Most of the sounds we hear reach our ears through the air, but sounds can also travel through and solids. If you swim underwater—or even submerge your ears in bathwater—any sounds you hear have traveled to your ears through the water. Some solids, including glass and , are very good at transmitting sounds. Foam rubber and heavy fabrics, on the other hand, tend to muffle sounds. They absorb rather than pass on the sound energy.
::我们听到的声音大多是通过空气听到的,但声音也可以穿透水体和固体。如果你在水下游泳,或者甚至将耳朵浸入浴水中,你听到的声音都从水中传到耳朵里。有些固体,包括玻璃和玻璃,非常擅长传出声音。 另一方面,泡沫橡胶和重织物往往会发出杂音,它们吸收而不是传递声音能量。Q: How can you tell that sounds travel through solids?
::问:你怎么看出来这听起来像是在固体中穿梭的?A: One way is that you can hear loud outdoor sounds such as sirens through closed windows and doors. You can also hear sounds through the inside walls of a house. For example, if you put your ear against a wall, you may be able to eavesdrop on a conversation in the next room—not that you would, of course.
::A: 一种方式是,你可以听到户外响亮的声音,比如通过封闭的窗户和门发出警笛,也可以从房屋的墙壁里听到声音。例如,如果你把耳朵放在墙上,你也许可以窃听隔壁房间的谈话——当然你不会窃听。Summary
::摘要-
In science, sound is defined as the transfer of energy from a vibrating object in waves that travel through matter.
::在科学中,声音的定义是,在物质流动的波浪中,振动物体的能量转移。 -
All sound waves begin with vibrating matter. The vibrations generate longitudinal waves that travel through matter in all directions.
::所有声波都从振动物质开始。振动产生纵向波,从各个方向穿行。 -
Most sounds we hear travel through air, but sounds can also travel through liquids and solids.
::我们听到的声音大多来自空中,但声音也可以来自液体和固体。
Review
::回顾-
How is sound defined in science? How does this definition differ from the common meaning of the word?
::科学如何界定声音?这个定义与这个词的共同含义有何不同? -
Hitting a drum, as shown in the
Figure
, generates sound waves. Create a diagram to show how the sound waves begin and how they reach a person’s ears.
::如图所示,敲鼓会产生声波。 创建图表以显示声波是如何开始的以及声波是如何到达一个人耳朵的。
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How do you think earplugs work?
::你觉得耳塞怎么用?
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In science, sound is defined as the transfer of energy from a vibrating object in waves that travel through matter.
