Notes

Outline

Dmitri Shostakovich (1906-1975)   Symphony No. 5  Last Movement (1937).

Introduction Examples of waves

Waves   A wave is an array of neighboring objects oscillating in a regular, progressive manner relative to one another.

Displacement vs. Position

Displacement vs. Time

Terminology  Frequency Number of oscillations per second  Wavelength Distance between adjacent crests  Amplitude Maximum displacement

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Types of Waves  Transverse Wave Particles oscillate perpendicular to the direction in which the wave moves  Longitudinal Wave Particles oscillate parallel to the direction in which the wave moves

Waves (Alternate Definition) A wave is a disturbance traveling outward from a vibrating source.

Sound Waves Produced by oscillating air molecules Longitudinal waves Periodic pressure variations are set up

Sound Waves The actual motion is molecular (microscopic).  Difficult to measure and visualize. The pressure changes are macroscopic.  Easy to measure and visualize.

Sound Waves  (1) When the pulse reaches a particular point, the pressure increases from normal atmospheric pressure to some maximum value.

Sound Waves  (2) As the pulse continues to move through the point, the pressure begins to return to normal atmospheric pressure.

Sound Waves  (3) As the trailing edge of the pulse approaches, the pressure falls below normal atmospheric pressure.

Sound Waves (4) When the pulse has passed, the pressure returns to normal atmospheric pressure.

Sound Waves (Pressure Variations)

Pressure vs. Position (at a fixed time)

Pressure vs. Time (at a fixed point)

Sound Waves A sound wave is a longitudinal wave with a frequency between 20 Hz and 20,000 Hz.

Sound Waves The frequency of a sound wave is always the same as the frequency of the vibrating source that produces it.

Sound Waves  frequencies < 20 Hz       INFRASOUND  frequencies > 20,000 Hz      ULTRASOUND

Velocity of Sound Waves

Velocity of Sound Waves

Velocity of Sound Waves   The velocity of any wave is directly proportional to the square root of the stiffness factor and inversely proportional to the square root of the inertia factor.

Speed of Sound in Air The speed of sound in air is:  344 meters per second  1030 feet per second  770 miles per hour

Effect of Temperature on Speed of Sound   The speed of sound changes by 0.6 m/s for every 1 degree change in the Celsius temperature.

Effect of Temperature on Speed of Sound If the temperature increases, the speed of sound increases. If the temperature decreases, the speed of sound decreases.

Energy In Sound Waves  Kinetic and Potential Energy  Larger Amplitude means more energy = louder

Relation Among Velocity, Frequency, and Wavelength v = f l

Physical/Perceived Musical Characteristics         Physical              Perceived    Characteristic       Characteristic       Frequency                Pitch       Amplitude             Loudness       Waveform               Timbre