Doppler effect is a change in frequency and wavelength of a wave. It is caused by the change in distance between the thing creating the wave (causer) and whatever is measuring (watcher or observer), seeing or hearing the wave.
Another word for "causer" is "sender". Another word for "change in distance" is "speed" or "relative velocity". A common example is sitting in a car while another car goes by the watcher. The watcher will hear a change in pitch, while the sender will not.
For waves read all the waves that can send out or reflected by a object. And for reflection read change of direction of a wave.
Effects of changes in distance
If observer and creator of the wave get closer, the frequency is higher and the wavelength is shorter.
- For light, this causes a shift in colour towards the blue end of the spectrum called a blueshift.
- For sound, this causes the sound to become higher in pitch
If the distance between the observer and creator gets longer, the frequency is lower and the wavelength is longer.
- For light, this causes a shift towards the red end of the spectrum called a redshift, the faster something is moving away, the greater the redshift.
- For sound, this causes the sound to become lower in pitch.
Lightwaves can also be read, examples are:
An extreme example of the doppler effect is an airplane flying at a faster speed than the speed of sound and how the wall of sound is heard on the ground.
Images for kids
Colour flow ultrasonography (Doppler) of a carotid artery - scanner and screen
Doppler effect Facts for Kids. Kiddle Encyclopedia.