Sound Waves: Properties and Velocity

Sound Propagation

• Sound waves are mechanical longitudinal waves, as they require a medium.
• The medium particles vibrate in the same direction as wave propagation, forming compressions and rarefactions.
• We hear sound from all directions due to its propagation as spheres of compressions and rarefactions.

Sound

• Sound is an external factor that affects the ear, and causes hearing.
• Sound travels through air at approximately 340 m/sec.

Sound Velocity

• Sound velocity (V) in meters/second = Frequency (F) in Hertz × Wavelength (λ).

Audible Sounds

• Audible sounds are classified into musical tones and noises.
  • Musical tones have uniform frequency and are comfortable.
  • Noises have non-uniform frequency and are uncomfortable.

Properties of Sound Waves

• The human ear distinguishes sounds through three properties: sound pitch, sound intensity, and sound quality.

Sound Pitch

• Sound pitch is the property that differentiates between harsh and sharp voices.
• A sound is either high pitched or low pitched:
  • High pitched sounds are sharp (soft).
  • Low pitched sounds are harsh (rough).
• For example, a woman's voice is high pitched, while a man's voice is low.
• The sound pitch depends on the frequency of the sound source.
• When sound pitch increases, frequency increases, and vice versa.
• Sharp tones have high frequencies, while harsh tones have low frequencies.
• The sound pitch depends on the length of the vibrating air column in cases of vibrating air columns.
  • As the length of the vibrating air column increases, the sound frequency decreases, so the harshness of sound heightens.
  • As the length of the vibrating air column decreases, the sound frequency increases, leading to sharpness of sound.

Sound Intensity

• Sound intensity is the property that differentiates between strong and weak sounds.
• Sound intensity is measured in "watt/m²".
• Noise intensity is measured in "Decibel".

Factors Affecting Sound Intensity

• Distance between the ear and the sound source.
  • Sound intensity is inversely proportional to the square of the distance.
• Amplitude of vibration of the sound source.
  • Sound intensity is directly proportional to the square of the amplitude.
    • The amplitude of the vibrating surface.
    • Sound intensity increases by increasing the vibrating surface area when the sound touches a resonance body (box).
• Medium density:
  • Sound intensity decreases by decreasing the density of the medium.
    • Sound intensity is directly proportional to the density of the medium.
• Wind direction:
  • The intensity of sound increases when the direction of sound waves is in the same direction of the wind.
  • The intensity of sound decreases when the direction of sound waves propagation is in the direct opposite of the wind.

Sound Quality (Type)

• Sound quality distinguishes different sounds based on the nature of the source even if they share the same intensity and the same pitch.
• Tones produced from a vibrating tuning fork is a pure simple tone that is also recognized as a fundamental (basic) tone.
• Tones produced from instruments such as violin or piano, consist of a fundamental tone associated with harmonic tones.
• Harmonic tones are higher in pitch and lower in intensity and vary depending on the source of the sound.

Sound Waves

• Infrasonic waves.
  • They are sound waves of frequencies lower than 20 Hz.
• Sonic waves.
  • They are sound waves of frequencies ranging from 20 Hz to 20 KHz.
• Ultrasonic waves.
  • They are sound waves of frequencies higher than 20 KHz (20000 Hz).
    • Some animals can hear ultrasonic waves and sonic waves.

Applications of Ultrasonic Waves

• Ultrasonic waves are used in:
  • Medical field: breaking down kidney and ureter stones, diagnosis of male prostate gland tumors, and discovering malignant tumors.
  • Industrial field: sterilization of food, water, and milk.
  • Military field: the discovery of landmines.

Explore the nature of sound waves as mechanical longitudinal waves. Understand how sound propagates through compressions and rarefactions. Learn about sound velocity and the properties that allow us to distinguish different sounds, including pitch, intensity, and quality.