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