First of all my respectful greetings to all the Hive.blog community, we continue with our wonderful journey through the understanding of the phenomenon of sound, and thus, with those phenomena intrinsic to its propagation, as is the case of the Doppler effect.

Introduction

Every human being with his normal hearing capacity is a reliable witness of any kind of audible sound that develops in our environment, and in addition, of those phenomena involved during its propagation, in this way we have related to phenomena such as reflection, absorption, diffraction, refraction, as well as sounds below our hearing capacity as the infra and ultra sound.

This time we will continue to relate to the recognized phenomenon of the Doppler effect and for the analysis of this phenomenon it is very important to take into account vital elements such as the sound emitting source and the receiver of the sound, since the understanding of the phenomenon of the Doppler effect will depend on their position, and we will begin to verify this from this article.

The Doppler effect and sound waves

It is always important to highlight that the phenomenon of the Doppler effect in relation to sound waves were first perceived by the excellent physicist, mathematician and astronomer Christian Andrés Doppler, that is why it bears his name, therefore, my dear friends before relating to this wonderful Doppler effect, I would like to show the following example in order to have a better understanding of this phenomenon, so I invite you to observe the following action of Figure 1.

_{Figure 1. Relationship between ball throws at the same frequency to a receiver at rest}

As you could see in Figure 1 above, we are involved with the velocity of a mobile (in this case a train), as well as with the velocity of firing of tennis balls, and with the frequency of firing of tennis balls, and also with a receiver in a stationary or immobile state.

We must express that the train travels at a constant or uniform speed, in addition, the speed with which the balls are thrown is also constant, as well as the throwing frequency, the latter can be set at one ball every 3 seconds, and as we can see in the previous figure, these tennis balls are sent to a receiver at rest.

Therefore, my dear readers, we can observe that the closer the train is to the receiver, the faster the balls will arrive, where it indicates that at a distance of 8 meters the ball takes 3 seconds to arrive at its destination, and each time we get closer this time decreases.

The previous action makes the receiver think that at a shorter distance both the speed and the frequency of launch are greater in relation to a longer distance, when both the speed and frequency of launch remain the same, and as we get closer and closer this action becomes faster making our receiver believe that the rate of the launch frequency and its speed have increased when really it is all in the distance between the source emitting the launches and the receiver.

Therefore, when relating it to sound waves we can express that when a source of sound emission approaches a certain receiver either at rest or in motion, these waves will arrive with a higher frequency, and thus, the sound will be sharper, but, when the source moves away from the receiver, the sound will be deeper as we can see in the following figure 2.

_{Figure 2. Sound emitter and receiver at rest (a), also with the sound source moving (b)}

With the previous figure we began to relate to the Doppler effect linked to sound, in this case both the emitter of sound and receiver at rest, as well as the emitter of sound waves in motion, in the following installments we will continue relating to other examples, where the position of the essential elements are involved as the source emitting the sound as the receiver.

Conclusion

Really wonderful phenomena occur around us that are an intrinsic part of our existence as is the case of the Doppler effect phenomenon, and thanks to science-technology we have achieved its understanding, and also, with the help of the field of education has been able to spread to the rest of the people.

In this opportunity we managed to relate the sound emitting source with a receiver and whose position of these elements were either at rest or in motion, and from this aspect depends on how the receiver manages to perceive the sound, as you could see in the previous images.

Until another installment, my dear Hive.blog readers.

Note: The images are my own and were created using Power Point and the animated gif was created with the PhotoScape application.

Recommended Bibliographic References

[1]Physics of sound

[2]Specular and diffuse sound reflection. Author: @rbalzan79.

[3]Sound absorption. Author: @rbalzan79.

[4]Sound transmission. Author: @rbalzan79.

[5]Sound diffraction. Author: @rbalzan79.

[6]Sound refraction. Author: @rbalzan79.

[7]Acoustic or sound spectrum. Author: @rbalzan79.

[8]The human ear and sound. Author: @rbalzan79.

[9]Infrasound.Author:@rbalzan79.

[10]Educating ourselves with infrasound, Some sources of generation. Author:@rbalzan79.

[11]Educating ourselves with ultrasound. Author:@rbalzan79.

[12]Educating ourselves with ultrasound / Application in navigation. Author:@rbalzan79.

[13]Ultrasound technology applied in medicine. Author:@rbalzan79.

[14]Natural frequency of oscillation and resonance. Author:@rbalzan79.

[15]The Doppler effect and its relationship between sound frequency and wavelength _Part I. Author:@rbalzan79.