When an ambulance passes with its siren blaring, you hear the pitch of the siren change: as it approaches, the siren’s pitch sounds higher than when it is moving away from you. This change is a common ...

We have all noticed how the horn of a speeding car changes as it approaches: each wave-peak is emitted from a closer point, so the wave is “squeezed” and the pitch increases. As the car recedes, the ...

Can't see the video? Download an mp4 [10.4 MB] version of this video. Smart phones are expensive so please take care not to swing yours too close to a wall or a person or inside a sock that's almost ...