Short Notes:

The Doppler effect is the well-known change in sound that occurs when the source of a sound is moving in relation to a listener. To the stationary listener, the sound appears to rise gradually in pitch as the source of the sound approaches, and then to fall as it continues past the listener. This so-called Doppler shift is caused by sound wave fronts that arrive in ever-greater frequency as the moving object nears the listener. The increase in frequency is accompanied by a shrinking of wavelength. The higher the frequency of a sound, the higher its pitch. When the object moves away from the listener, the reverse takes place. Frequency drops, wavelength increases, and the apparent tone of the sound that the listener hears becomes lower and lower.

The Doppler effect can be commonly heard in passing train whistles, ambulance or police sirens, and jet plane engines.

Click here for a Flash presentation on Doppler effect (vehicle).

Click here for a Flash presentation on Doppler effect (bell).