来自《耶鲁大学开放课程：生物医学工程探索 第21集 第21集》
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that's coming towards you and the horn is honking.这辆车在不断地鸣着警笛 -
As the car is approaching you,随着这辆离你越来越近 -
you hear a certain frequency of sound你所听到声音的频率 -
that changes as the car passes. The frequency of the sound会随着汽车的接近而改变 -
that you hear depends both on the frequency of the sound你所听到声音的频率 -
that's being emitted by the siren and the speed既取决警笛这个声源的发声频率 -
that the ambulance is moving relative to you.还取决于救护车相对于你的速度 -
When the ambulance is moving towards you,当救护车向你驶来时 -
you hear a frequency that's你所听到的声音的频率 -
offset from the real frequency of the siren.不同于警笛发出声音的频率 -
When it's moving away from you its offset even more当它离你而去时 差别就更大了 -
and you can hear that.你们能够听出这种差别