This effect can be observed when a person shouts in a valley. The sound waves travel to the nearby mountains and get reflected. The person thus hears back his own voice. The time taken by the sound waves to return back depends upon the distance between the persons and the mountains. The similar concept is applied in RADAR. Here radio waves are emitted by the RADAR which travel in all directions. If an object comes in the way of these waves they get reflected back with the speed of light and detected by the RADAR. By knowing the time elapsed between sending and receiving back the waves, the position of the object can be determined by calculating the distance the wave has travelled.
Now in order to calculate the speed of an object the concept of Doppler shift plays its role. When a wave is reflected by a moving object its nature depends upon the movement of that object. If the object is moving towards the source of the wave, then the pitch of the wave will be higher than if it is moving away from it. This can be observed in case of a car blowing its horn. When a moving car approaches a person the horn seems to be louder and when it moves away it become s somewhat fainter. Knowing the pitch of the sound wave the speed of the car can be detected. This principle is applied in case of RADAR where a radio wave is used instead of a sound wave. ...Show more