章节大纲

  • 常规

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  • 多普勒效果

    An airplane creates a vapor cone as it travels faster than sound, producing a sonic boom.

    At normal speeds, when an object generates sound, the sound travels away from the object and people hear the same sound that was generated by the object. In some unusual cases, like this airplane, the object can travel as fast or faster than the sounds it makes. The moves along with this airplane; as the airplane continues to generate more sound, this sound is added to the old sound. When this extra large sound wave front arrives, the sound is much louder than the sound that was originally generated. When this happens with airplanes, the sound is called a “sonic boom.”
    ::正常速度, 当一个物体产生声音时, 声音会远离该物体, 人们会听到与该物体产生的声音相同的声音。 在一些不寻常的情况下, 比如这架飞机, 该物体可以比它发出的声音快或快。 与这架飞机一起移动; 当飞机继续产生更多声音时, 这个声音会添加到老声音中。 当这个额外的大声波前方到达时, 声音会比最初产生的声音更响亮。 当这发生在飞机上时, 这个声音被称为“ 音响 ” 。

    Doppler Shift
    ::Doppler 移动

    If an emitted sound is moving at a significant fraction of the relative to the receiver, it is possible for the sound emitted by a source and the sound received by a receiver to be different. This is called a Doppler shift.
    ::如果发出的声音在相对于接收器的相当部分移动,则源发出的声音和接收器收到的声音有可能不同。这称为多普勒转换。

    Suppose the trumpet player in the sketch below is playing a constant note with a equal to 1.00 m/s. If you are sitting down the road a ways and the truck is stationary, then the wavelength of the sound that reaches you will be 1.00 m long and you will hear a note corresponding to that wavelength. Suppose now, that the speed of sound is 333 m/s and this truck is moving toward you at 166. m/s. When the trumpet player begins playing the tone, the first crest will move toward you at 333 m/s. In the first 0.003 seconds, that first crest will move exactly 1.00 m (which happens to be one wavelength for this sound). After the trumpet player generates the first crest, however, the truck also moves and in the first 0.003 seconds, the truck moves 0.50 m. After the first 0.003 seconds, the trumpet player creates a second crest and sends it on its way. When this second crest is generated, the first crest is only 0.50 m away. If the truck did not move, the crests would reach your ear with a wavelength of 1.00 m, but because the truck moves toward you at very high , the crests reach your ear at a of only 0.50 m apart. Therefore, the sound you hear will have shorter wavelengths than the sound that was emitted by the trumpet player. The frequency of the sound you hear would be double the frequency that was being emitted.
    ::假设下面草图中的小号手正在播放一个固定的音符,其音量等于1.00米/秒。 如果您坐在路边的道路上, 卡车是固定的, 那么到达您的声音的波长将是1. 00米长, 您将会听到一个与波长相应的音符。 假设现在, 声音的速度是333米/秒, 而这辆卡车正在以166米/ 秒的速度向您移动。 当小号手开始播放音调时, 第一个曲轴会以333米/秒的速度向您移动。 在最初的0.003秒中, 第一个曲轴会完全移动1米( 碰巧是这个音调的波长)。 在吹喇叭手生成第一个牛胸后, 卡车移动的音速是0. 50米。 在头0. 00秒后, 喇叭播放器会创造第二个曲轴, 并发送它。 当这个第二曲轴开始响时, 第一个曲轴只会在0. 50米外移动。 如果卡车不移动, 最曲轴会以1米的频程到达您的耳朵, 。 因此, 音轴会以1 m 0 m 。 音调的音 。

    A trumpet player on a moving truck demonstrates the Doppler shift concept in sound waves.

    If the truck was moving away from you, the opposite change of frequency would occur.  That is, the received wavelength would be longer than the one emitted and the received frequency would be lower than the frequency emitted. You may have noticed frequency changes in automobile sounds when you stand near a highway. Or that an emergency vehicle's siren is different when approaching you than when leaving. 
    ::如果卡车离你而去,频率就会发生相反的变化。 也就是说, 接收的波长会比发出的波长长, 接收的频率会比发出的频率要低。 当你站在高速公路附近时, 您可能注意到汽车声音的频率变化。 或者, 紧急车的警报器在接近你时会与离开时不同 。

    Tuning fork emitting sound waves, illustrating the Doppler Effect with frequency changes.

    You can also hear the Doppler shift in the classroom simply by striking a tuning fork and then moving the tuning sharply toward you or away from you.  Even though the tuning fork generates a constant tone, you will hear wavering tones as you move the tuning fork around.
    ::您也可以听到多普勒在课堂上的转变,只需敲响一个调速叉,然后把调速叉向上移动,或者从你身边移动。即使调速叉产生一个不变的音调,当调速叉向周围移动时,您也会听到摇晃的音调。

    Comparison of sound wave patterns from a stationary and moving train to illustrate Doppler Shift.

    In terms of the listener, the train sketched on the left above is not moving and therefore the wavelengths and frequency heard in all directions will be the same as the frequency being emitted. For the train on the right, however, since the train is moving toward the right, the wavelengths measured to the right will be shorter than those emitted and the wavelengths measured to the left will be longer than those emitted.
    ::就听众而言,上面左侧绘制的列车没有移动,因此,各个方向听到的波长和频率将与所发射的频率相同。 但是,对于右边的列车来说,由于火车向右移动,测到右边的波长将比所发射的短,测到左边的波长将比所发射的长。

    Christian Doppler (1803 – 1853) did experiments in 1842 with trumpeters playing a single note as they sat on a railroad flatcar and were pulled back and forth past a stationary observer. The Doppler effect also occurs when the source of the sound is stationary and the observer is moving (with a significant fraction of the speed of sound). The following formulas have been developed for calculating the observed frequency:
    ::1842年克里斯蒂安·多普勒(1803 - 1853年)在小号手坐在一辆铁路平板汽车上时弹了一个音符,然后被拖过固定的观察者。 多普勒效应也发生在声音的来源是静止的而且观察者正在移动时(音速是音速的相当一部分 ) 。 以下公式是用来计算所观察到的频率的:

    When the source is moving toward you, f o = f 1 − v R v .
    ::当源代码向您移动时, fo=f1-vRv 。

    when the source is moving away from you, f o = f 1 + v R v .
    ::当源代码正在从您移动时, fo=f1+vRv 。

    In the equations f o is the perceived frequency,  f is the emitted frequency,  v R is the relative and  v is the speed of sound.
    ::方程式Fo是感知频率, f是发射频率, vR是相对的, v是声音的速度。

    Example  
    ::示例示例示例示例

    The speed of sound is 340. m/s and a train whistle with a frequency of 512 Hz is emitted from a train coming toward you at 40.0 m/s. What frequency will you hear?
    ::声音的速度是340米/秒, 频率为512赫兹的火车哨声是从40米/秒的火车上射出的。 你会听到什么频率?

      f o = f 1 − v R v = 512   s − 1 1 − 40.0   m / s 340.   m / s = 580   H z
    ::=f1-vRv=512 s-11-40.0 m/s340.m/s=580 Hz

    Use the Doppler Ducks simulation below to adjust how quickly a duck and boat move through the water. Positive velocities are rightward and negative velocities are leftward. Try playing around with having the duck go faster or slower than the , or towards or away from the boat. Be sure to observe the doppler shape in the water waves when the duck is moving more slowly than the wave speed. What happens when the duck moves more quickly than the wave speed? Launch the simulation to find out:
    ::使用下面的 Doppler ducks 模拟来调整鸭子和船在水中移动的速度。 正速是右向的, 负速是左向的。 尝试让鸭子走得比船快或慢, 或者朝向或离船更慢。 当鸭子移动速度比波速慢时, 一定要观察水波中的多普勒形状 。 当鸭子移动速度比波速更快时会发生什么情况 ? 启动模拟以了解 :

    Summary
    ::摘要

    • The Doppler shift, or Doppler effect, occurs when a sound's emission and the sound's receiver travel relative to each other at a significant speed compared to the speed of sound.
      ::多普勒转换,即多普勒效应,发生于声音的发射和声音接收器彼此相对的移动时,与声音的速度相比,速度相当快。
    • If the sender and receiver are getting closer together, the perceived frequency will be higher than the emitted frequency, given by the equation   f o = f 1 − v R v .
      ::如果发件人和接收人越来越接近,根据方程式fo=f1-vRv的计算,感知频率将高于所发射的频率。
    • If the sender and receiver are getting farther apart, the perceived frequency will be lower than the emitted frequency, given by the equation  f o = f 1 + v R v .
      ::如果发件人和接收人越分越远,根据方程式 fo=f1+vRv 所显示的频率将低于所发射的频率。

    Review
    ::回顾

    1. What is the frequency heard by a person driving at 15 m/s toward a blowing factory whistle if the emitted frequency is 800. Hz and the speed of sound is 340. m/s?
      ::以15米/秒开往吹风厂口哨的人听到的频率是多少,如果所发射的频率是800。赫兹和声音的速度是340米/秒?
    2. While standing near a railroad crossing, a person hears a distant train horn.  According to the train’s engineer, the frequency emitted by the horn is 440 Hz and the train is traveling toward the railroad crossing at 20.0 m/s.  If the speed of sound is 340 m/s, what frequency will the observer hear?
      ::当一个人站在铁路过境点附近时,听到一个遥远的火车角。 据火车工程师说,喇叭的频率是440赫兹,火车正以20米/秒的速度驶向铁路过境点。 如果声音的速度是340米/秒,观察者会听到什么频率?
    3. After the train passed the person at the crossing, what frequency would he hear?
      ::火车经过过过境点的人后,他能听到多少次?

    Explore More
    ::探索更多

    Use this resource to answer the questions that follow.
    ::使用此资源回答下面的问题 。

    1. What is necessary for a wave source / receiver to observe a Doppler Effect?
      ::波源/接收器观测多普勒效应需要什么?
    2. What happens to the frequency as a wave source approaches an observer? moves away from an observer?
      ::当波源接近观察者时频率会怎样?远离观察者?
    3. Do all types of waves (sound, water, light) experience the Doppler Effect?
      ::所有类型的波(声音、水、光)是否都经历过多普勒效应?