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SOUND

What is Sound?

Sound is a form of energy, produced by rapidly vibrating objects, that can be heard by the human ear.

Sound is a longitudinal wave.

Most young people respond to sound frequencies of between 20 Hz and 20 000 Hz.

Infrasonic- any sound with a frequency lower than 20Hz

Ultrasonic- any sound with a frequency above 20 000 Hz

How is Sound Produced?

▪ Sound is produced by a vibrating object.

(vocal chords, guitar strings, lips blowing into a trumpet)

▪ Sound needs a material medium for its transmission.

▪ Sound cannot travel through a vacuum.

When a tuning fork is struck, it vibrates. As the tines move back and forth, rarefactions and compressions follow one another as the sound waves travel through the air away from the tuning fork.

GRAPHING SOUND WAVES

Sound waves are graphed as transverse waves (using the sine function from math).

Sound waves are waves of high pressure and low pressure.

Compression: area of high air pressure

Rarefaction: area of low air pressure

pitch loudness

Pitch is related to the frequency of Loudness is related to the amplitude of

sound waves. sound waves.

THE SPEED OF SOUND

The speed of sound depends on temperature and the properties of the material.

In general, the stiffer the material, the faster the speed of sound.

The speed of sound air can be calculated using

[pic]

where v is the speed of sound in metres per second (m/s)

t is temperature in degrees Celcius (oC)

example 1

Calculate speed of sound at

a) 0.00oC

b) -15.0oC

c) 20.0oC

estimating lightning distance

|REFLECTION | |

| |angle of reflection = angle of |

|[pic] |incidence |

| | |

|DIFFRACTION | |

|[pic] |The bending effect on a wave’s direction as it passes through an |

| |opening or by an obstacle. |

| |Sound waves have the ability to move around an obstacle or to spread|

| |out after going through a small opening. |

| | |

|REFRACTION | |

|[pic] |The bending effect on a wave’s direction that occurs when the wave |

| |enters a different medium at an angle. |

| |Sound waves travel faster in warm air than in cold air. |

| |

example 2 A student stands 86 m from the foot of a cliff, claps her hands, and hears the echo 0.50 s later. Calculate the speed of sound in air.

example 3 A sonar device is used in a lake, and the interval between the production of a sound and the reception of the echo is found to be 0.40 s. The speed of sound in water is 1500 m/s. What is the water depth?

SOUND INTENSITY

The amount of sound energy being transferred per unit area. (units: W/m2)

decibel (dB): the unit of sound level used to describe sound intensity level

[pic]

LOUDNESS , DISTANCE AND SOUND SAFETY

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HOMEFUN

-8.5 Properties of Sound Waves read pg 392-397

-finish examples in lesson handout

-pg397 #4-6,8b

HOMEFUN

8.5 Properties of Sound Waves read pg 392-397

finish examples in lesson handout & pg397 #4-6,8b

Read 10.1 Human Ear

Read 10.3 Acoustics

Read 10.7 Nature & Sound

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