This demonstration works only on Internet Explorer
If your computer is equipped with sound you will hear a demonstration of the doppler effect.
The car is moving at about 30 miles/hour. You can hear that it is sounding its horn. You only observe the doppler effect as the car passes you and starts moving away. At that time you hear a sudden drop in the frequency (pitch) of the horn. As the car was approaching the frequency you heard was actually higher than the frequency being emitted by the horn. As the car moved away the frequency you heard is LOWER than that being emitted. The sudden shift from higher to lower frequency is quite dramatic.