sec1 sound waves handout

Sound Waves - SPHSC 261 Module 1

1. Sound Sources

2. Medium Requirement

  • A medium is necessary for sound propagation.

  • Common medium: Air

3. Atmospheric Pressure

  • Atmospheric pressure (P0) affects sound propagation.

4. Compression and Rarefaction

  • Compression: Atmospheric pressure (P > P0) indicates a phase where sound waves are concentrated.

  • Rarefaction: Atmospheric pressure (P < P0) indicates a phase where sound waves are less concentrated.

5. Sound Wave Characteristics

  • The oscillation of a sound source creates alternating patterns of compression and rarefaction that propagate away from the source.

  • The variations in pressure constitute a sound wave.

  • Individual air particles move locally back and forth, not traveling with the wave.

6. Nature of Sound Waves

  • Sound waves are pressure waves.

  • Sound source: Requires vibration to create waves.

  • Medium: Must be elastic; in air, sound waves appear as pressure waves.

  • Sound pressure: Refers to the deviation from atmospheric pressure.

    • Positive sound pressure indicates pressure greater than atmospheric pressure.

7. Longitudinal Wave

  • Sound waves are classified as longitudinal waves.

  • Air particles' movement is parallel to the direction of wave propagation.

8. Speed of Sound

  • Speed is dependent on the medium's properties.

  • Faster propagation in stiffer (harder) media.

  • Speed Measurement: Measured in meters per second (m/s).

  • Speed Values by Medium:

    • Air: 343 m/s

    • Water: 1433 m/s

    • Sea water: 1560 m/s

    • Concrete: 3200-3600 m/s

    • Steel: 6100 m/s

    • Diamond: 12000 m/s

9. Measuring Sound Waves

  • Waveform: Plots sound pressure versus time (in seconds).

    • Example waveform shows variations in pressure recorded over time.

10. Pressure Measurement

  • Pressure is expressed in Pascals (Pa).

    • Atmospheric pressure at sea level is approximately:

      • 101,300 Pa

      • 1.013 bar

      • 14.7 psi

11. Units of Measurement

  • US vs SI Units:

    • Distance: inches/feet/yards vs meters

    • Volume: various US units vs liters/m³

    • Mass: ounces/pounds vs kilograms

    • Pressure Reading: psi (US) and kPa (SI).

12. Physical Quantities and Their Units

  • Distance: mm, m, km

  • Mass: mg, g, kg

  • Time: ms, sec

  • Volume: L, m³

  • Velocity: m/s

  • Density: kg/m³

  • Pressure: mPa, Pascal, kPa

13. SI Unit System Abbreviations and Values

  • Abbreviations:

    • μ-: micro- (10^-6)

    • m-: milli- (10^-3)

    • c-: centi- (10^-2)

    • k-: kilo- (10^3)

  • Example Calculations:

    • 0.2 mPa = 0.0002 Pa

    • 2.45 kPa = 2450 Pa

14. Summary

  • To produce sound waves, a vibrating sound source and medium are required.

  • Sound waves are pressure waves consisting of patterns of compression and rarefaction.

  • Sound pressure characterizes deviations from atmospheric pressure.

  • Sound waves are longitudinal, with particles moving back and forth in the direction of the waves.

  • The speed of sound varies by medium density, with a faster speed in harder materials.

  • The sound pressure unit in the SI system is Pascal (Pa).