• Sound is a form of energy produced by the
vibration of matter.
• Sound is a compressional or longitudinal wave
• Sound is transmitted through solids, liquids,
• Sound is transmitted better through
solids and liquids. Why?
• Gases transmits sound a lot farther
than a solid and liquid. Why?
–Less dense; not as many
particles to interfere.
• So what causes sounds to travel better
through some substances and not
–The greater the elasticity, the
greater the speed.
–The greater the density, the slower
–The best conductors of sound are
• Sound can not be transmitted
through a vacuum.
–Sound needs a medium in order
for it to be transmitted.
• Radio waves can travel through a
vacuum; no medium is needed.
–This is why astronauts can use
radio signals to talk in space.
Speed of Sound
• 344 m/s in air at 20°C
• Depends on:
– Type of medium
• travels better through liquids and solids
• can’t travel through a vacuum
– Temperature of medium
• travels faster at higher temps
The denser the medium, the
faster sound will travel.
The higher the temperature, the
faster the particles of the
medium will move and the faster
the particles will carry the sound.
Sound travels through different media.
We hear sound which usually travels through air. Sound
travels through other media as well, such as water and
Sound travels different speeds in different media. Sound
typically travels faster in a solid that a liquid and faster in
a liquid than a gas.
Parts of the ear
• Outer ear: pinna
• Ear canal
• Ear drum: tympanum
–Vibrates the ear drum
• Middle ear: three small bones
• Inner ear
–Cochlea: filled with fluid
•Hair-like nerve endings
• Damage done to the hairs
causes permanent hearing
loss. The hairs never grow
B. Human Hearing
vibrates ear drum
nerve impulses in
– highness or
lowness of a
– depends on
– human range: 20
- 20,000 Hz
FREQUENCIES YOU CANNOT HEAR
•Ultrasonic: higher than 20,000 Hz
Uses: clean jewelry, medical
•Infrasonic: lower than 20 Hz
Found: in the atmosphere and
in the crust when plates move; also
an indication motion sickness
– volume of sound
– depends on energy (amplitude) of sound wave
– measured in decibels (dB)
Above 120 dB can cause hearing loss
• Doppler Effect
– change in wave frequency
caused by a moving wave source
moving toward you -
pitch sounds higher
moving away from you
- pitch sounds lower
What is the Doppler Effect?
The Doppler Effect is the apparent change in frequency
detected when the sound is moving relative to the
Reflection of Sound Waves
• Echolocation: process using reflected sound
waves to find objects
Seeing with Sound
• Ultrasonic waves - above 20,000 Hz
Medical Imaging SONAR
“Sound Navigation and Ranging”
What is sonar?
Sonar is a system that uses the reflection of underwater
sound waves to detect objects. This has been used to
find sunken ships and schools of fish.
• Bends of waves around or through a barrier
2.Someone in the hallway
on the other side and we
can hear them.
Constructive - louder
– the ability of 2 or more waves to combine to form a
Destructive - softer
– variations in sound
intensity produced by 2
– both constructive
–The effects caused by 2 or
•Ex. Several instruments
produce interference in
Cool Interference Examples:
• The Sound Barrier: the point at which the
source of a sound accelerates to the speed of
• Sonic Booms: the explosive sound heard when
a shock wave reaches your ears
time sound barrier broken: Oct. 14, 1947 by
Chuck Yeager (speed of sound is called Mach
1); so Mach 6 is going 6 times the speed of
• Forced Vibration
– when one vibrating object forces
another object to vibrate at the
– results in a louder sound because a
greater surface area is vibrating
– used in guitars, pianos, etc.
– special case of forced
– object is induced to vibrate
at its natural frequency
– the lowest natural frequency of an object
– multiples of the fundamental frequency