The Doppler Effect is the apparent change in the frequency of the sound, light or radio waves caused by the relative motion between the source of the waves and their receiver. For example, the pitch of a police car siren as the care speeds by depends on the whether the car is moving towards or away from you. As the car approaches, the sound waves ahead of it are bunched up. These short waves have a high frequency so the siren sounds high. Behind the car, the waves are stretched out.
These longer waves have a lower frequency so the siren sounds lower as the care drives past. In actual fact, the frequency of the siren does not change at all. Christian Doppler, who was an Austrian scientist, was the first to record the effect and hence the name was given.
These longer waves have a lower frequency so the siren sounds lower as the care drives past. In actual fact, the frequency of the siren does not change at all. Christian Doppler, who was an Austrian scientist, was the first to record the effect and hence the name was given.