The Doppler Effect Explained

What is the Doppler Effect?

If any object moves through the air, there will naturally be disturbances in that air. The disturbances are referred to as sound waves. If an object were to stand still in the same position while making these disturbances, the sound waves would move at the same pace with the same frequency in all directions around the object. This would mean that an observer 20 meters to the right (Observer A) would observe the sound waves approaching at the same frequency as an observer 20 meters to the left (Observer B) would.

Now imagine that the object is moving to the right, while creating sound waves at the same frequency as before. Since the object is moving to the right, every consecutive disturbance would be closer to observer A, and farther away from observer B. Therefore, each consecutive disturbance also has a shorter distance to travel to reach observer A, thus taking a shorter amount of time to do exactly that. Because of this, observer A observes that the frequency of arrival of the disturbances is higher than the frequency at which disturbances are actually produced. At the same time, each consecutive disturbance has to travel an even longer distance in order to reach observer B. For this reason, observer A observes a frequency of arrival that is less than the frequency at which the disturbances are produced. The net effect of the object's production of disturbances is that the observer the object is moving towards observes a higher frequency than the pace of which the disturbances are produced, while the observer on the opposite side observes a lower frequency that the pace of which the disturbances are produced. This effect is called the Doppler Effect.