Physics: Oscillatory Motion and Sound

Production of Sound

• Sound is produced as a result of vibrations.
• Vibration is rapid to-and-fro or up and down movement about a mean position.
• Air molecules around vibrating bodies transmit vibrations through various media to ears.
• Vibrations can be heard, seen, or felt.
• Wind creates sound only when it strikes something in its path.
• Vibrations can be produced by:
  • plucking stretched strings like in guitar, sitar and violin.
  • striking stretched skin like in drum, tabla and dholak.
  • vibrating air column like in flute.

Characteristics of Sound

• Sounds can be identified and differentiated by their respective sources and characteristics.
• Pitch and loudness are two main characteristics that help distinguish different types of sound.
• Amplitude, time period, and frequency are characteristics of vibrations.

Oscillatory Motion of a Simple Pendulum

• The to-and-fro or back-and-forth movement, called oscillatory motion, is similar to vibrating tuning fork prongs or guitar strings.
• A simple pendulum consists of a small bob attached to a string.
• If the bob is pulled to one side and released, it exhibits oscillatory motion.
• The mean position of the bob is at A, where it remains at rest.
• One oscillation is completed when the bob moves from A to B, then B to A, and from C back to A.

Amplitude

• The maximum displacement of the bob from the mean position on either side (AB or AC) is the amplitude of the pendulum, measured in meters (m).

Time Period

• The time taken to complete one oscillation is the time period, measured in seconds (s).
• If the movement is very rapid, the time period for 10 oscillations is measured and divided by 10 to find the time period of one oscillation.

Frequency

• Frequency is the number of oscillations completed in one second, measured in hertz (Hz).
• If a pendulum makes 10 oscillations per second, its frequency is 10 Hz.
• The frequency of tuning forks is written on them, typically 512 Hz, which means it produces 512 vibrations in one second.

Relation Between Frequency and Time Period

• If the frequency of a vibrating body is represented by f and the time period is represented by T, then T = 1/f.

Pitch

• Pitch is the measure of the shrillness of a sound.
• A sound with a high frequency has a high pitch and is called shrill.
• A sound with a low frequency has a low pitch and is called gruff.
• Females usually have shrill voices, while males have gruff or deep voices.

Sounds produced by musical instruments - pitch influenced by:

• the length of the string
• the thickness of the strings
• how tight/loose the strings are

Loudness

• Loudness depends on the amplitude of the sound wave.
• A larger amplitude produces a louder sound, while a smaller amplitude produces a soft sound.

Quality or Timbre

• When two people have the same pitch and loudness but have voices that sound different.
• Timbre depends on the source of sound.

Propagation of Sound

• Sound requires a medium for propagation, such as solids, liquids, and gases.
• When an object vibrates in air, it disturbs the air particles, causing them to vibrate and transfer the sound.
• Sound cannot propagate through a vacuum because it lacks particles to pass on vibrations.

How Humans Hear Sound

• Sounds are vibrations produced in the air around us, which is enabled by our ears.
• The ear consists of the outer ear, middle ear, and inner ear.

Outer Ear

• The outer ear includes the pinna and ear canal, leading to the eardrum.
• The ear canal leads to the eardrum
• Sound waves lead into the eardrum which vibrates.

Middle Ear

• The eardrum vibrations from the outer ear make their way to the middle ear
• The middle ear contains 3 small bones, hammer, anvil, and stirrup.
• The middle ear bones finally transmit the vibrations to the inner ear

Inner Ear

• The inner ear contains the cochlea which contains fluid.
• Sound vibrations get passed from the fluid to the auditory nerve
• The brain interprets these signals as sounds

Speed of Sound

• The speed of sound is measured in meters per second (m/s).
• The speed of sound varies in different mediums; it is highest in solids and lowest in gases.
• Sound travels fastest in solids and slowest in gases.
• As temperature increases, the speed of sound also increases.
• Speed of sound for different medium:
  • Air: 330 m/s (at 0°C), 343 m/s (at 25°C)
  • Water: 1484 m/s
  • Aluminum: 5100 m/s
  • Steel: 6100 m/s

Explore oscillatory motion and sound with our physics guide. Learn about tuning forks, pendulum motion, frequency measurement, and sound pitch. Understand key concepts like mean position and maximum displacement.