Transcript Sound waves with frequencies less than 20 Hz. They are produced

Chapter 12.1-SOUND
4. SPEED OF SOUND
• Much slower than
light
• Thunder and
Lightning
– Five second delay per
mile
• Depends on wind,
temperature, humidity
The Speed of Sound depends on the density of the medium
through which the sound waves travel.
Medium
Air at 20° C
Distilled Water 25°
C
Seawater 25° C
Steel
In ft./s In m/s
1116 340
4908 1496
5023 1531
17100 5200
Reflection
Loudness is related to the
energy (amplitude) in
the sound wave.
The pitch of a sound
refers to whether it is
high, like a flute,
or low like string bass.
The lower the frequency
of sound, the lower the pitch.
ENERGY IN SOUND WAVES
• Energy in sound is weak when
compared to the energy in light.
• The human ear is a remarkable
detector.
10 million people speaking at the same
time produce approximately enough
energy to light one flashlight.
Loudness Intensity
measured in decibels
Pitch
• Relative highness or
lowness of a note.
• adding PITCH to
rhythm and
amplitude creates
melody
• A sound that
vibrates back and
forth 1,000 times
per second like a
tuning fork has a
frequency of a
1,000 Hz
• The frequency of
the human auditory
system has a range
from 20 Hz to
20,000 Hz
• Frequencies for
musical notes
Octave
• a pitch an octave higher than another has
[ii:20] double its frequency
– Example: 440 Hertz * 2 = 880 Hertz
• a pitch an octave lower has [ii:21] half the
frequency
– Example: 440 Hertz * .5 = 220 Hertz
A3
A4
A5
Standing waves in instruments
• Guitar & all stringed
instruments have
sounding boards or boxes
to amplify sound!
• (hyperlink on picture)
•
• Anything above
frequencies, anything
above 20,000 Hz
• Used for communication
and navigation by bats
and dolphins
 Ultrasonic waves are
short
 Widespread medical
applications
 Used to produce images
inside the human body
 hyperlinks on each image
• Sound waves with
frequencies less than 20 Hz.
• They are produced by such
things as heavy machinery
and thunder.
• They are really low pitched
sounds.
• Elephants can communicate
from kilometers away using
infrasonic waves.
Elephants “hear” through their feet.
• Flexible, soft skin of the
foot acts like a drum
head, which sense
vibrations which travel
from the toe nails to the
ear by bone conduction.
Foot stomping and low
frequency rumbling
generated by one group
of elephants are picked
up by another group far
away.
FORCED VIBRATIONS
• Demo - Tuning Fork Touching a Table
• Sound is intensified because of the larger
surface area that can vibrate the air.
• The surface is forced to vibrate at the
frequency of the tuning fork. (It is not a
resonance phenomenon.)
• Examples: Musical sounding boards
NATURAL FREQUENCY
• Demo - Drop Different Sounding
Objects
• Objects have natural frequencies at which
they vibrate.
• The natural frequency depends on elasticity
and shape.
RESONANCE
• Resonance occurs
when we force a
vibration at the
• same frequency in
• another object.
Middle Ear Schematic