Explain why the sound of a speeding car or emergency vehicle seems to lower in pitch as the vehicle passes by. Use the Doppler effect in your...


The Doppler effect is a phenomenon that occurs when a person listening to a sound source, such as an approaching ambulance, experiences a rise or fall in the pitch of the sound.  This occurs as the ambulance is approaching because the sound waves are pushed together, giving an apparent rise in pitch.  As the ambulance passes by and is now leaving, the sound waves are stretched apart, resulting in an apparent drop in pitch.  The effect is even more pronounced if the listener is in a vehicle and is traveling in the opposite direction of the ambulance, there is a noticeable drop in the pitch as the ambulance passes by the listeners vehicle and both vehicles speed off in different directions.  To answer your 2nd question, if both the listener and the ambulance were moving in the same direction at the same speed, there would be no noticeable change in pitch or sound.  For question 3, there would be the same effect described initially, where the sound waves are compressed, resulting in an upwards shift of the pitch.

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