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The Nature of Sound
Section 2:
Properties of Sound
Essential Questions
How does the speed of sound differ in different media?
How are frequency and pitch related?
What is the Doppler Effect?
How are amplitude and loudness related?
How can frequency and amplitude be “seen” on an oscilloscope?
Vocabulary
Pitch – depends on frequency of the sound wave; measures how high or low a sound is perceived
Doppler Effect – change in frequency of a sound wave when the source or observer is moving
Loudness – extent to which a sound can be heard
Decibel – the most common unit to measure loudness: symbol is dB
The Speed of Sound
Speed of sound depends on its’ medium
• Sound travels fastest in solids, second fastest in liquids, and more slowly through air
Temperature also effects the speed of sound
• The cooler the medium, the slower the sound
Pitch and Frequency
Pitch – how high or low a sound seems
Frequency – the number of crests or troughs in a given time
• Expressed in hertz (Hz): 1 Hz = 1 wave/second
Pitch and frequency are related
Sounds that have a frequency too high for people to hear are called ultrasonic
The Doppler Effect
The Doppler effect is the apparent change in frequency of a sound caused by the motion of the listener or the source
Movement causes the compressions and rarefactions to be closer together or further apart; this is why the frequency and pitch change
Loudness and Amplitude Loudness is a measure of how well a
sound can be heard
• More energy = larger vibrations = louder sounds
Increasing energy increases amplitude
• Amplitude of a wave is the largest distance particles vibrate from the rest position
• Larger amplitude = louder sound
• Smaller amplitude = smaller sound
Measuring Sound
Unit used to express loudness is the decibel (dB)
Oscilloscope – graphic representations of sound waves