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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. Speed of Sound. The Speed of Sound depends on the density of the medium through which the sound waves travel. Reflection. - PowerPoint PPT Presentation
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Chapter 12.1-SOUND
4. SPEED OF SOUND• Much slower than
light• Thunder and Thunder and
LightningLightning– 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 In ft./s In m/sAir at 20° C 1116 340Distilled Water 25° C
4908 1496
Seawater 25° C 5023 1531Steel 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 Intensitymeasured 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 TableDemo - 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 Demo - Drop Different Sounding
ObjectsObjects
• 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