what is sound and how is it produced
Sound
|
INTRODUCTION A world without
sound can be imagined only with mixed feelings of horror and fun. The
beautiful songs, the chirping of the birds and learned discourses would have
existed only in dreams. There would have been a lot of misunderstanding right
from individuals to the nations as no one could have been able to speak to
somebody else, what to talk of hearing each other. Two individuals engaged in
an effort to talk to each other, might have been misunderstood as jeering at
each other like monkeys, resulting possibly in a quarrel. In these strange
circumstances, the ear would have been absolutely useless and so would be the
tongue and lips to a large extent. We can extend this imagination to any
limit of fantasy, resulting in greater and greater consolation that nothing
really exists like this. The study of sound
is largely based on the classical contribution of Helmholtz and Lord
Reyleigh. The Acoustical Society of America was founded in 1928 and, today,
both universities and industrial research laboratories, such as Bell
Telephone Laboratories are engaged in important investigations in the field
of theoretical and applied sound. The significance of sound in human
communication has grown rapidly with developments in radio, television and
recorded speech and music. In this chapter, we
shall consider simple physical aspects of sound, its mode of production and
propagation, its nature and its role in our daily life. WHAT IS SOUND ? We must understand
at the outset that the word sound has two distinct meanings. 1. Subjective or
psychological meaning which refers to auditory (hearing) sensation which
ceases when the sound sensing organ (ear) is withdrawn from the scene. 2. Objective or
physical meaning which refers to the energy reaching the ear from outside.
The energy continues to propagate even if no ear is present to detect it. From our present
point of view, sound is mechanical energy which produces sensation of
hearing. The perception of
sound is largely physiological in nature. However, to a great extent, what we
'hear' NOTE is the result of the way our nervous system acts in response to
sound stimuli. Hence, the term psychology of sound'. Recently, the mental or
psychological aspect of sound production has been made a field of study known
as psychoacoustics. PRODUCTION OF SOUND In order to know
how sound is produced, let us perform the following two simple experiments. Experiment 1. Take a metallic wire AB and stretch it
tightly between two nails fixed on a table top. When we pluck the wire, a
sound is heard. If a V-shaped small paper rider (R) is placed near the centre
of the wire, it starts vibrating and in case, the rider is at the centre of
the wire, it flies off, This proves that the sound is produced due to
vibrations in the wire. Experiment 2. Strike a bell, B with a hammer, it produces sound. On touching it with
finger, we feel that the bell is in a state of vibration. A pith-ball, P
suspended near the bell moves from its equilibrium position P to P’. This
again demonstrates that the sound is produced due to vibrations in the bell. Thus, sound is produced by vibrating objects. PROPAGATION OF SOUND We have just learnt that sound is produced by vibrating
objects. In order to reach the listener, it passes through a medium which may
be a liquid, a solid or a gas. Let us now briefly discuss as to how sound
travels from the source to the listener. (i) The vibrating object sets the particles of the inedium
around it into vibration (i.e., to and fro motion). (ii) A particle (say 1), which is in contact with the
vibrating object moves towards the right (say). This particle exerts a force
on a neigh bouring particle (2) which is displaced from its equilibrium
position and also starts moving towards right. After displacing particle (2),
particle (1) comes back to its original position whereas particle (2) exerts
a force on particle (3) in a similar fashion. This process, in which each
particle strikes its (a) neighbour while vibrating without leaving its mean
position, continues till the particle near the listener's ear starts
vibrating. All particles of the medium between the source of sound and the
listener are set vibrating in the (b) similar fashion and the sound is
carried to the listener. It is important to note that the particles of the medium
only vibrate and do not actually move from the vibrating body to the
listener. Once the vibrations of the source stop, the particles no longer
vibrate and no sound reaches the listener. Thus, sound created by the source reaches the listener
through the particles of the medium without any net transport of the medium. In fact, whatever travels through the medium is a
disturbance carrying sound energy. This disturbance is called a sound wave
and the motion associated with this wave is called wave motion. Thus, Wave motion is a form of disturbance (a mode of energy
transfer) which is due to repeated vibrations of the particles of the medium
about their mean positions and the motion is handed over from one particle to
the other without any net transport of the medium. Since sound waves are produced by the vibrations of the
particles of the medium, these are called mechanical waves. In fact, whenever
sound waves travel, it is the energy that is transferred from the source to
the listener without the motion of the medium. On Your Tips 1.
All liquids and gases are called fluids. 2.
A fluid contained in a vessel exerts pressure at all points of the vessel and
in all directions and it increases with depth inside the liquid. 3.
Pascal's law states that the pressure applied at any place to an enclosed
mass of a fluid is transmitted equally in all directions and it acts
undiminished at every point of the fluid and on the walls of the container. 4.
When a solid body is fully or partially immersed in a fluid, the fluid exerts
an upward force on the body which is called upthrust, buoyant force or force
of buoyancy. 5.
The upthrust on a body arises on account of a difference of pressure between
the lower and upper
parts of the body. 6.
A body having density greater than that of a liquid sinks into it while a
body having density smaller than that of the liquid floats on it. 7.
When a body is immersed partially or wholly in a liquid at rest, it
experiences an upthrust which is equal to the weight of the liquid displaced.
This is known as Archimedes' Principle. 8.
Upthrust or buoyant force (FB) acting on a body immersed in a liquid 9.
Apparent weight of a body in a liquid = true weight of the body (W) - weight
of the liquid displaced by the body (W). |
0 Comments