根据多普勒效应,光被离子反射后,靠近激光器的光的频率会高于远离激光器的光的频率,(日常生活中,救护车警报器的音调随着车的远近也变化,就是这个道理)这才有可能测量先前对离子施加的力的大小。
(An everyday example of this effect is the change of pitch of an ambulance siren as it approaches and recedes.) It was thus possible to measure the force applied to the ions.
玛丽听到了救护车刺耳的警报声。
另一个例子是“警报器”这个词,是我们很熟悉的一个机械装置,当警车、救护车或消防车靠近时,警报器会发出警报。
Another example is the word siren, familiar to us as the mechanical device that makes such an alarming sound when police cars, ambulances, or fire engines approach.
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