CONCEPTS AT A GLANCE The Doppler effect arises when the source and the observer of the sound wave have different velocities with respect to the medium through which the sound travels. At a racing event, the Doppler effect creates the characteristic sound that you hear when the cars pass by. It is similar to that heard when a train blowing its horn passes you at a high speed. ( Simon Bruty/Stone/Getty Imates)

Figure 16.28 CONCEPTS AT A GLANCE The Doppler effect arises when the source and the observer of the sound wave have different velocities with respect to the medium through which the sound travels. At a racing event, the Doppler effect creates the characteristic sound that you hear when the cars pass by. It is similar to that heard when a train blowing its horn passes you at a high speed. (© Simon Bruty/Stone/Getty Imates)