Biomedical Engineering Reference
In-Depth Information
1 Elements of the Description
There is a wide range of physical phenomena behind birdsong. Physics al-
lows us to understand what mechanisms are used in order to generate the
song, what parameters must be controlled, and what part of the complex-
ity of the sound is the result of the physics involved in its generation. The
understanding of these processes will take us on a journey in which we
shall visit classical mechanics, the theory of fluids [Landau and Lifshitz 1991,
Feynman et al. 1970], and even some modern areas of physics such as non-
linear dynamics [Solari et al. 1996]. Ultimately, all these processes will be
related to the sounds of birdsong described in this text. For this reason, it
is appropriate to begin with a qualitative description of sound. Even if it is
likely that the reader is familiar with the concepts being discussed, this will
allow us to establish definitions of some elements that will be useful in our
description and analysis of birdsong.
1.1 Sound
1.1.1 A Metaphor
Let us imagine a group of people standing in line, with a small distance
between each other. Let us assume that the last person in the line tumbles
and, in order to avoid falling, extends his/her arms, pushing forward the
person in front. This person, in turn, reacts just like the person that pushed
him/her: in order to avoid falling, this person pushes the person in front,
and so on. None of the people in the line undergoes a net displacement, since
every person has reacted by pushing someone else, and returning immediately
to their original position. However, the “push” does propagate from the end
of the line to the beginning. In fact, the first person in line can also try to
avoid falling, by pushing some object in front of him/her. In other words,
he/she can do work if the object moves after the push. It is important to
realize that the propagation of this “push” along the line occurs thanks to
local
displacements of each of the persons in the line: each person moves just a
small distance around their original position although the “push” propagates
all along the line.
