Chapter 5 Sound and Waves

ISCI 2002 Integrated Science

• Instructor: Dr. Shameer Abdeen

• Chapter 5: Wave Motions and Sound

5.1 Forces and Elastic Materials

• All oscillations involve force and energy.

• Vibration: A back-and-forth motion that repeats itself.

• Spring example:

  • Applied force is proportional to distance (compression/stretching).

  • Internal restoring force returns to original shape, proportional to displacement.

• Simple Harmonic Motion:

  • Defined by restoring force opposite to and proportional to displacement.

Important Concepts

• Amplitude: Extent of displacement from equilibrium position.

• Equilibrium Position: Total force acting on a mechanical system is zero.

• Cycle: Complete vibration.

• Frequency (f): Number of cycles per second (Hertz).

• Period (T): Time required for one complete cycle.

5.2 Waves

• Mechanical waves require a medium for propagation; they move through the medium while the medium remains in place.

• Types of Waves:

  • Mechanical Waves: Can be transverse or longitudinal.

  • Electromagnetic Waves: Do not require a medium.

  • Matter Waves: Quantum mechanical phenomena.

Transverse and Longitudinal Waves

• Transverse Waves:

  • Particles oscillate perpendicular to wave direction.

  • Example: Waves on a string.

• Longitudinal Waves:

  • Particles oscillate parallel to wave direction.

  • Example: Sound waves in air.

5.3 Describing Waves

• Waves properties: frequency, wavelength, amplitude, and velocity.

• Wavelength: Distance between points of identical phase.

• Amplitude: Maximum displacement from equilibrium, determines intensity.

• Wave Equation: Highlights relationship between wavelength, frequency, and velocity.

5.4 Sound Waves

• Sound waves are mechanical longitudinal waves.

• Result from vibration/oscillation creating pressure fluctuations in a medium.

• Properties of Sound Waves:

  • Wavelength: Distance between compressions.

  • Amplitude: Difference between compressions and rarefactions (volume).

  • Frequency: Number of waves passing per second (pitch).

• Velocity of Sound: Speed varies with medium; typically ~340 m/s in air.

• Refraction: Change of direction due to speed/density change in mediums.

• Reflection: Sound wave bounces back when encountering a surface.

• Interference: Waves combine, leading to constructive and destructive interference.

Special Effects of Waves

• Beats: Rhythmic volume changes from interference of two sound waves of different frequencies.

• Sonic Boom: Effect created when a source exceeds the speed of sound.

5.5 Energy and Sound

• Intensity: Measure of energy carried by a wave (watts/m²), measured in decibels.

• Loudness: Subjective perception related to various factors including distance and environmental conditions.

• Resonance: Occurs when an object vibrates at its natural frequency due to an external force.

5.6 Sources of Sound

• All sounds originate from vibrating objects.

• Vibrating Strings: Concepts of waves in strings, reflected waves, constructive and destructive interference.

• Doppler Effect: Change in frequency due to the motion of the source or observer.

• Standing Waves: Occur at resonant frequencies, characterized by nodes and antinodes.