chapter 3 class on 1.16

Sound and Waves

• Definition of Sound

  • Sound is produced by vibrating objects; vibrations create oscillations in air.

  • Only objects with inertia can vibrate and generate sound.

• Nature of Sound Propagation

  • Sound waves are a result of oscillations or back-and-forth motion of air molecules.

  • Example: A pendulum swings when a force is applied, illustrating the concepts of inertia and elasticity.

  • After being displaced, the pendulum returns to rest due to elasticity but continues swinging due to inertia, creating oscillations until energy is dissipated, often as heat.

Wave Types

• Longitudinal vs Transverse Waves

  • Longitudinal Waves: Sound is a longitudinal wave; particles move parallel to the direction of wave propagation.

  • Transverse Waves: Ripple effects in water are examples of transverse waves where particle motion is perpendicular to wave direction.

• Examples of Longitudinal Waves:

  • When speaking, air molecules are disturbed, creating a domino effect as displaced molecules push adjacent particles, resulting in sound propagation.

Frequency and Pitch

• Frequency: Number of cycles produced per second by vibrating objects (measured in Hertz).

• Pitch: Psychological perception associated with frequency.

  • Higher frequency correlates with higher perceived pitch; frequency is a physical measurement, while pitch is subjective.

• Inverse relationship between frequency and period:

  • Frequency = 1/Period; Higher frequency = shorter period and vice versa.

Wave Amplitude and Intensity

• Amplitude: Refers to the maximum extent of displacement from rest; links to sound intensity.

• Intensity: The sound power per unit area; decreases with distance from the sound source.

• Doubling distance reduces intensity by a factor of four.

Wave Properties

• Wave Length: Distance traveled by a wave in one cycle; inversely related to frequency (higher frequency = shorter wavelength).

• Velocity of Sound: Travels at different speeds through various media (faster in solids than in liquids and gases).

Harmonics and Complex Sounds

• Sine Waves: Fundamental building blocks of sound with single frequency.

• Complex Sounds: Combinations of multiple sine waves; can be analyzed through Fourier analysis to identify constituent frequencies.

• Fundamental Frequency: Lowest frequency in a complex sound, perceived as pitch; all harmonics relate to this frequency.

• Vocal Production:

  • Vocal folds generate sound, but articulation shapes the output.

  • Articulators (tongue, lips, etc.) modify the sound after generation, affecting speech quality.

Sound Propagation Mechanics

• Sound propagates through molecular motion; pressure changes create areas of high and low density (compressions and rarefactions).

• In a medium, air particles vibrate around their equilibrium positions, transferring energy to adjacent particles resulting in sound transmission.

• Sound undergoes reflection, diffraction, and interference, which impacts its quality and clarity in different environments.