Why is it when cars that blast music pass my house the pitch/tone of the song and singer changes?
In: Physics
That’s the Doppler effect in action. Sound transmits to our ears as pressure waves in the air around us. A vehicle that is making noise while it is in motion is actually shortening the wavelength of the sounds it is sending your way by moving towards you while making sound, hence raising its pitch. As it moves away from you, it is artificially lengthening its sound waves thus lowering the pitch of the sound as perceived by you. The real pitch of the sound as experienced inside the vehicle (that is, from a FRAME OF REFERENCE with zero RELATIVE VELOCITY to the sound’s source) is actually somewhere between the two pitches you hear as it approaches then recedes.
It’s called the doppler effect.
Sound is waves or vibrations in the air; closer together waves make higher pitched sound, further apart waves make lower pitch. If the source of the sound is moving towards you the waves are squeezed even closer together and the pitch gets higher, if the source is moving away the waves spread out more and the pitch gets lower.
Aside from hearing this with cars blasting music, it’s also very noticeable when an emergency vehicle with a siren passes by.
It even works with light in space; if a star or other light emitting object is moving away from earth its light will get a bit redder (lower frequency), if it’s moving towards earth its light will get a bit bluer (higher frequency).
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