What Causes the ‘Doppler Effect’ in Sound?

Imagine you're on a playground, and a friend is riding a bike while ringing a bell. When they come toward you, the sound of the bell seems to get higher, like it's shouting at you. But when they ride away, the sound gets lower, almost like it’s whispering. This change in pitch happens because of the Doppler Effect. It’s all about how waves move and how we hear them.

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Examples

  1. A fire truck siren sounds higher as it approaches and lower as it drives away.
  2. A friend on a bike with a bell seems to shout when coming toward you, then whisper as they pass by.
  3. When a train whistles while moving closer, the sound is sharper, like a high note, but softens as it moves away.

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