When a siren approaches you the wavelength of the sound decreases, corresponding to an increase in frequency which we perceive as increase in the pitch of the sound. This is known as the Doppler Effect or Dopper Shift. You've probably noticed that as a siren, train whistle or loud engine passes you it gets higher in pitch as it approaches and decreases in pitch as it moves away. Since the source of the sound waves is moving with the waves, the wave fronts bunch closer together in front of the moving source and stretch further apart behind the moving source. When the wave fronts are closer together the wavelength is shorter and the frequency of the waves is higher.
The linked video shows how this happens. It also explains Red Shift, which is the change in wavelength of light that is emitted by moving objects.
No comments:
Post a Comment