Sound is a mechanical
wave that is
an oscillation of pressure
a solid, liquid, or gas,
of frequencies within the
range of hearing.
Propagation of sound
The behaviour of sound propagation is generally affected by
• A relationship between density and pressure. This
relationship, affected by temperature, determines the speed of
sound within the medium.
• The propagation is also affected by the motion of the medium
itself. For example, sound moving through wind. Independent
of the motion of sound through the medium, if the medium is
moving, the sound is further transported.
• The viscosity of the medium also affects the motion of sound
waves. It determines the rate at which sound is attenuated.
For many media, such as air or water, attenuation due to
viscosity is negligible.
Perception of sound
The perception of sound in any organism
is limited to a certain range of
frequencies. For humans, hearing is
normally limited to frequencies between
about 20 Hz and 20,000 Hz (20 kHz).
The scientific study of human sound
perception is known as psychoacoustics.
Types Of Sound Waves
Two types of waves:
Longitudinal sound waves are waves
of alternating pressure deviations from
the equilibrium pressure, causing local
regions of compression and rarefaction.
Sound is a longitudinal wave.
A transverse wave is a
moving wave that consists of
oscillations occurring perpendicular (or
right angled) to the direction of energy
transfer. Light is a transverse wave.
Properties of Sound
A sound is a vibration
The vibrating causes the air molecules
near the movement to be forced closer.
This is called compression
As the vibration moves on, the density
and air pressure becomes lower than
normal and is called rarefaction.
Pressure wave – longitudinal
v = 334 m/s in air at room temperature
Velocity is dependent upon the
• The Doppler effect is the change
in frequency of a wave (or other periodic
event) for an observer moving relative to its
• The received frequency is higher
(compared to the emitted frequency) during
the approach, it is identical at the instant of
passing by, and it is lower during the
Speed Of Sound
Sound travels faster in warm water
than in cold water.
By measuring the time it takes for
sound to travel a known distance
through the ocean the average
temperature of the water can be
• Also called LOUDNESS
• Amount of energy
• Depends on the amplitude of sound
L a r g e A mp . = L o u d s o u n d
S ma l l
A mp . = S o f t
s o u n d
•Sound waves reflecting from
•Ex.: Multiple echo resulting
from the direct sound and
the reflected sound
• Sonar (originally
an acronym for SOund Na
vigation And Ranging) is
a technique that
uses sound propagation
to navigate, communicate
with or detect objects on
or under the surface of
the water, such as other
• Used to locate
underwater objects and
Ultrasound can be used to create internal images of
the human body
Ex. Pregnant woman gets a “picture” of her unborn baby