What is Doppler Effect and it's applications?

The apparent change in frequency of sound due to relative motion between the source and observer is called Doppler effect. 

Applications of Doppler effect::

1. The speed and the direction of motion of submarines can be calculated.
2. Doppler effect is useful for the police to determine the speed of automobiles that are approaching and moving away.
3. Doppler effect is used to find the velocity of approaching and receding stars.
4. This is useful to measure the radical speed of satellites.
5. Double stars and Saturn's ring were discovered using doppler effect.