The Doppler effect describes the change in the observed of a wave when there is relative motion between the wave source and the observer. *
4 points
Amplitude
Interference
Wavelength
Frequency

The Doppler effect describes the change in the observed Frequency of a wave when there is relative motion between the wave source and the observer.

Explanation:

• Doppler described, How the color of the Starlight changed  with the Movement of the star.

•  Waves comes in variety of forms.

There are two common factors that used to describe all types of waves,

1. Wavelength, 2. Frequency.

•  For waves that carries light, the frequency of it determines the color of the light it carries.

In relate the the first and last point of the above contexts,

We conclude that the Doppler effect describes the change in the observed frequency of a wave when there is relative motion between the wave source and the observer

friction

explanation:

they us to move forward and backwards