Chapter 24 –SoundChapter 24 –Sound

24.1 –Properties of Sound24.1 –Properties of Sound

pp. 578 - 582pp. 578 - 582

SPEED OF SOUNDSPEED OF SOUND

•Depends on the Depends on the medium through which it is traveling. .

•Changes when the Changes when the medium changes..

•Sound travels faster in steel than in Sound travels faster in steel than in water.water.

•Speed of sound Speed of sound depends on temperature. The cooler the The cooler the temperature, the slower the speed temperature, the slower the speed of sound.of sound.

24.1 The speed of sound24.1 The speed of sound• The speed of sound The speed of sound

in normal air is 343 in normal air is 343 meters per second meters per second (660 miles per hour).(660 miles per hour).

• Sound travels Sound travels through most liquids through most liquids and solids and solids faster than through air..

• Sound travels about Sound travels about five times faster in five times faster in water, and about 18 water, and about 18 times faster in steel.times faster in steel.

24.1 The speed of sound24.1 The speed of sound

• Objects that move Objects that move faster than sound faster than sound are called are called supersonic..

• If you were on the If you were on the ground watching a ground watching a supersonic plane fly supersonic plane fly toward you, there toward you, there would be silence.would be silence.

The sound would be behind the plane, racing to catch up.

24.1 The speed of sound24.1 The speed of sound

• Passenger jets are Passenger jets are subsonic because because they travel at speeds from 400 to 500 they travel at speeds from 400 to 500 mi/hr.mi/hr.

PITCHPITCH

• The pitch of a The pitch of a sound is sound is determined by the frequency of the sound wave..

• High pitch = High pitch = high frequency

• Low pitch = Low pitch = low frequency

24.1 The frequency of 24.1 The frequency of soundsound• Almost all the sounds you hear contain Almost all the sounds you hear contain

many frequencies at the same time.

• Humans can generally hear frequencies Humans can generally hear frequencies between between 20 Hz and 20,000 Hz..

FREQUENCIES YOU CANNOT FREQUENCIES YOU CANNOT HEARHEAR

• Sounds with frequencies lower than 20 Sounds with frequencies lower than 20 Hz are called Hz are called infrasonic..

• ““Infra” means “Infra” means “below”.”.• Sounds with frequencies higher than Sounds with frequencies higher than

20,000 Hz are called 20,000 Hz are called ultrasonic..• ““Ultra” means “Ultra” means “beyond””• Ultrasonic waves are used to clean Ultrasonic waves are used to clean

jewelry and to remove ice from metal.jewelry and to remove ice from metal.

24.1 The frequency of 24.1 The frequency of soundsound• Sounds near 2,000 Hz Sounds near 2,000 Hz

seem seem louder than louder than sounds of other sounds of other frequencies, even at frequencies, even at the same decibel the same decibel level.level.

• According to this According to this curve, a 25 dB sound curve, a 25 dB sound at 1,000 Hz sounds at 1,000 Hz sounds just as loud as an 40 just as loud as an 40 dB sound at 100 Hz.dB sound at 100 Hz.

THE DOPPLER EFFECTTHE DOPPLER EFFECT• For sound waves, the Doppler effect is For sound waves, the Doppler effect is the

apparent change in frequency of a sound caused by the motion of either the listener or the source of the sound.

LOUDNESSLOUDNESS

• Loudness is related to Loudness is related to amplitude..

• The higher the amplitude of the The higher the amplitude of the wave, the wave, the louder the sound is..

• The lower the amplitude of the wave, The lower the amplitude of the wave, the the softer the sound is..

• Loudness is measured in Loudness is measured in decibels (dB).

SEEING SOUNDSSEEING SOUNDS

•An An oscilloscope is used to is used to graph graph representatiorepresentations of sound ns of sound waves.waves.

HOW IT WORKSHOW IT WORKS

• A microphone converts the sound A microphone converts the sound waves into an electric current.waves into an electric current.

• The oscilloscope converts the electric The oscilloscope converts the electric current into graphs. The highest current into graphs. The highest point (crests) represent point (crests) represent compressions of the sound wave; the of the sound wave; the lowest point (trough) represents lowest point (trough) represents rarefactions..