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Sound

All sounds are caused by something that
vibrates
 Sound waves – a longitudinal wave that is
caused by vibrations and that travels through a
material medium
– formed when a vibrating object collides with air
molecules, transferring energy to them,
Two regions of Compressional waves:
– Compressions
– Rarefactions
 They push air molecules together and then
spread them apart

3 Types of Mechanical Waves:
– Transverse
– Longitudinal
– Surface

Particles in a medium can vibrate either up and
down or back and forth.
 Waves are often classified by the direction that the
particles in the medium move as a wave passes by.

Mechanical waves require a medium to travel
 Transverse – causes the medium to vibrate in a
direction perpendicular to the direction the wave
travels
– Light waves
Longitudinal - particles of the medium vibrate
parallel to the direction of wave motion.
• Sound waves
•
Surface - particles move in circles.
• Surface waves occur at the boundary between two
different mediums, such as between water and air.
• The particles move both perpendicularly and parallel to
the direction that the wave travels
Light does not require a medium.
• Light waves consist of changing electric and
magnetic fields in space.
• Are electromagnetic waves
Electromagnetic wave - oscillating electric
and magnetic fields, which radiate outward at
the speed of light.
Amplitude measures the amount of particle
vibration.
• Crest - highest point of a transverse wave.
• Trough - lowest point of a transverse wave.
• Amplitude - maximum distance that the particles of a
wave’s medium vibrate from their rest position.

Wavelength measures the distance between two
equivalent parts of a wave.
• wavelength  - distance from any point on a wave to an
identical point on the next wave.
• Not all waves have a single wavelength that is easy to
measure.
The Electromagnetic Spectrum
Visible light
Wave Speed

Wave speed equals frequency times
wavelength.
distance
speed =
time
d
=
t
wavelength
speed =
period

=
T
speed = frequency  wavelength
 = f 

Medium – the type of matter, liquid, solid,
or gas; that sound waves travel through
– A sound wave’s speed depends on the
substance of the medium and whether the
medium is solid, liquid, or gas
– Sound travels more quickly through
solids and liquids b/c the individual
molecules are closer together than the
molecules in gas
– As a medium’s temperature increases, its
molecules move faster and it conducts
sound waves faster
Speed of Sound

The amount of energy a wave carries
corresponds to its amplitude, which is
related to the density of the particles in the
compressions and rarefactions
 Intensity – the amount of energy that flows
through a certain area in a specific amount
of time
 Loudness – human perception of sound
intensity
 Decibel – scale of measurement for sound
intensity
Pitch – how low or high a sound seems to
be
 Frequency - # of compressions or
rarefactions of a sound wave that pass per
second; human eats can hear frequencies
from about 20-20,000 Hz
 Ultrasonic waves - are sound frequencies
over 20,000 Hz, have medical and scientific
uses
 Subsonic waves – frequencies below 20
Hz, usually can’t be heard by may feel like
a rumble

Doppler effect – change in pitch or wave
frequency due to a moving wave source –
either the source of the wave or the observer
can be moving
 Music – sounds that are deliberately used in
a regular pattern
 Natural frequency – frequency at which
the material vibrates
 Resonance – the ability of a medium to
vibrate by absorbing energy at its own
natural frequency


Sound Quality – the differences among
sounds of the same pitch and loudness
Fundamental frequency – the main tone
played and heard
 Overtone – vibration with a frequency that
is a multiple of the fundamental frequency


Musical instruments – devices used to make
musical sounds

Types of musical instruments:
– Strings – instruments in which sound is
produced by plucking, striking, or drawing
a bow across tightly stretched strings
– Brass or woodwinds – air vibration in a
resonator, with the pitch determined by the
length of the vibrating tube of air
– Percussion – produce sound by being
struck, shaken, rubbed, or brushed
 resonator - hollow chamber that amplifies
sound
 Beats – a pulsing vibration in loudness

Uses of sound:
– Entertainment
– Warning signals
– Information
Acoustics –study of sound, which can prevent
excessive reverberation and create good
listening environments
Echolocation – process of locating objects by
sending out sounds and interpreting the
waves reflected back

Sonar – a system that uses the reflection of
underwater sound waves to locate objects

Ultrasound waves – are used in medicine
to diagnose, monitor, and treat many
conditions
– Can produce images of internal structures
for detection of medical problems
– Can treat certain medical problems such
as kidney stones or gallstones

Humans hear sound waves in a limited frequency
range.
• Any sound with a frequency below the range of
human hearing is known as an infrasound.

An infrasound is slow vibrations of
frequencies lower than 20 Hz.
• Any sound with a frequency above human hearing
range is known as an ultrasound.

An ultrasound is any sound wave with
frequencies higher than 20 000 Hz.
Speed of Light

4 stages of Human hearing:
– Eardrum – (tympanic membrane) sound
waves pass through membrane
– Middle ear – after the vibrations pass
through the eardrum they enter the
middle ear (incus, malleus, stapes)
– Cochlea – spiral shaped structure that
contains hair cells
– Auditory nerve – the hair cells vibrate
sending impulses along the nerve to the
brain