Sound is produced
in a material medium when the source vibrates in time. The vibrating
source compresses the part of medium next to it when it moves forward and then
increases pressure in that region (compression area).
When the vibrating source
moves backwards, a low pressure region (rarefaction) is
created. This pattern of pressure changes
continues cyclically. Sound is thus this disturbance (of compressions and
rarefactions) travelling at a fixed speed in the medium. The sound
waves are also called longitudinal waves. Sound travels in terms of mechanical waves
created by vibration of particles in the direction of propagation. Sound cannot travel with out a medium or in vacuum.
velocity of sound = √ ( Bulk modulus / density of medium)
Velocity of sound in air at
normal pressure and temperature is about 340 m/sec. Sound travels faster
in a denser medium, due to high bulk modulus. Sound is
produced due to conversion of energy from other forms. Sound waves have a frequency f of
vibration and a wavelength λ. The wavelength is the distance between two
successive rarefactions or two successive compressions.
velocity v = f * λ
When two sound waves meet each
other, then there is an interference between them. The waves may destruct
each other or add to each other , depending on their phase
difference. There are various characteristics of sound wave.
Pitch is the measure of
shrillness in a voice. Female voice has a higher pitch and a buffalo's
voice has a low pitch. Higher frequency gives a higher pitch. Loudness of sound is related to the
sound level, which is measured as logarithm of intensity of energy (or power)
in the wave. It is measured in decibels. We can hear sound waves of
frequency from 0 hertz to 20 kHz in general.
A combination of frequencies produced by a musical
instrument is different from the combination of frequencies produced by
another. The quality of sound depends on the combination. A musical instrument produces
waves with a frequency (fundamental frequency) as well as its integral
multiples (called harmonic notes).
When a moving car or train
approaches a siren, then the (apparent) frequency heard by the person inside
the train or car is different from the actual frequency of the siren
source. This is called Doppler's effect. The Doppler effect is used by
RADAR's to estimate the speed of approaching airplanes.
Intensity and Energy in a sound wave are proportional to square
Interiors of various community halls or theaters are designed for proper
acoustics, taking into account the reflections of sound waves from the ceiling
and side walls.
Energy is defined as capability to do work.
Work is useful way of consumption of energy. When a force moves an object over a distance, Work done = Force *
Displacement * Cos θ, where θ is the angle between force vector and displacement.
When an object falls
through a height h, the work done by the gravitational field of Earth is equal
to force * displacement = m g h. When work is done by
(on) the system, its total energy reduces (increases) by the amount equal to the work
Work energy theorem says that the work done is equal to the
change in kinetic energy of the system.Work done when a gas expands from volume V1 to V2 at
a constant pressure P is equal to P (V2 - V1). Work done when a mass m moves in a
gravitational field due to a mass M at a distance d is G M m / d. Work done when an electric charge q moves across a
voltage V is equal to qV. Work done when a rope is twisted by an angle θ is equal to
1/2 K θ^2.
Energy is the ability to perform useful work. Work is done
when a change occurs in positions or speeds of objects or friction
is overcome etc.Energy is inherently
present in all matter as E = m c^2, given by A. Einstein. There are
different forms of energy.
Energy is divided into two
types. Potential and kinetic. Kinetic energy is associated with the
movement of objects. Potential energy is dependent on the position of the
object in a field.Forms of energy are Mechanical, Sound energy
(kinetic), Gravitational potential energy, Electrical potential energy,
Magnetic potential energy, chemical energy (in terms of attractions of atoms,
molecules), nuclear energy (due to sub atomic particles), heat energy,
electromagnetic radiation energy.
Heat energy is the form of energy that flows from one
system to another depending on gradient in temperature. Chemical energy
is the energy released (absorbed) when bonds between atoms and molecules are
broken and formed in chemical compounds.Kinetic energy of a body of mass m with a
velocity v is equal to 1/2 m v^2. Energy stored in a spring (of spring constant k) when it
is compressed by an amount x is equal to 1/2 k x^2.