Sound Waves Notes

Physical Science Overview

  • Physical Science encompasses Chemistry, Physics, and Integrated Physics and Chemistry (IPC).

Chapter 12: Sound

  • Section 1 focuses on Sound Waves.

  • Key components of a sound wave include:

    • Source

    • Peak

    • Wavelength

    • Trough

    • Waveform

    • RMS locations

    • Wavelength

Introduction to Waves

  • A wave is a disturbance in a medium that carries energy without the movement of particles.

  • A medium is a physical environment through which a disturbance can travel.

    • Example: Water is the medium for ripple waves in a pond.

Types of Waves

  • Mechanical Waves

    • Require a medium to transfer energy.

    • Cannot transmit energy through a vacuum.

    • Examples: Sound and water waves.

  • Non-Mechanical Waves

    • Do not require a medium to transfer energy.

    • Can transmit energy through a vacuum.

    • Examples: Light, radio, ultraviolet, x-rays.

Mechanical Waves: Longitudinal vs. Transverse

  • Longitudinal Waves

  • Transverse Waves

    • Crest

    • Wavelength

    • Trough

    • Cycle

    • Amplitude

    • Direction of travel

Properties of Transverse and Longitudinal Waves

  • Transverse Waves

    • Particles vibrate perpendicularly to the direction of wave propagation.

    • Form crests and troughs.

    • Occur on the surface of solids and liquids.

    • Energy transfer is perpendicular to oscillations.

  • Longitudinal Waves

    • Particles vibrate parallel to the direction of wave propagation.

    • Form compressions and rarefactions.

    • Occur in solids, liquids, and gases.

Wave Definitions

  • Transverse Wave: Particles vibrate perpendicularly to the direction of wave motion.

    • Crest: Highest point, high density & high pressure above equilibrium.

    • Trough: Lowest point, low density & low pressure below equilibrium.

  • Longitudinal Wave: Particles vibrate parallel to the direction of wave motion.

    • Crests correspond to compression (high density and pressure).

    • Troughs correspond to rarefaction (low density and pressure).

Wavelength

  • Wavelength (λ\lambda) is the distance between two adjacent crests or troughs.

  • Amplitude is the maximum displacement (height) of a crest or trough.

  • Frequency is the number of cycles or waves per unit of time.

Sound Waves as Longitudinal Waves

  • Sound waves are longitudinal waves.

  • The simplest longitudinal wave produced by a vibrating object can be represented by a sine curve.

Sound Wave Production

  • A series of compressions and rarefactions forms and spreads away from a vibrating object (e.g., tuning fork prongs).

  • These compressions and rarefactions spread in all directions, like ripple waves on a pond.

  • When a tuning fork vibrates with simple harmonic motion, the air molecules also vibrate back and forth with simple harmonic motion.

  • Every sound wave begins with a vibrating object.

Frequency of Sound Waves

  • Frequency of sound waves (or pitch) is measured in hertz (Hz).

  • Humans have a normal hearing range between 20-20,000 Hz.

  • Infrasound: < 20 Hz (e.g., produced by elephants, moles)

  • Ultrasound: > 20,000 Hz (e.g., produced by bats, dolphins)

Frequency and Pitch

  • The frequency of an audible sound wave determines the pitch.

  • As frequency increases, the pitch rises.

  • Frequency is an objective quantity, while pitch is subjective.

  • Greater frequency is perceived as a higher pitch.

  • Frequency is the rate of particle vibration, while pitch depends on the listener.

Speed of Sound in Various Media

  • The speed of sound depends on the medium.

  • Waves consist of particle vibrations, and speed depends on how quickly one particle transfers motion to another.

  • Sound generally travels faster through solids than gases because molecules are closer together in solids.

  • The speed of sound also depends on the temperature of the medium, especially in gases.

Doppler Effect

  • The Doppler Effect is an observed change in frequency when there is relative motion between the source of waves and an observer.

Review Questions

  • When a part of a sound wave travels from air into water, frequency remains unchanged.

  • If a sound seems to be getting louder, intensity is probably increasing.

  • The Doppler effect does NOT occur when a listener and source of sound remain at rest.

  • A dog can hear a dog whistle because dogs detect sounds of higher frequency than humans.

  • Sound waves are transmitted in air by compressions and rarefactions.

Quick Wits Questions

  1. A wave that can travel only through medium is mechanical wave.

  2. The empty space is called vacuum.

  3. A material in which a mechanical wave travels is called medium.

  4. Mechanical waves can not move through vacuum.

  5. Sound waves and water waves are mechanical waves.

  6. An electromagnetic wave is a wave that can travel through vacuum and medium.

  7. Light and ultraviolet waves are non-mechanical waves.## Additional Resources

  • Textbook pages: 407-413

  • Videos:

    • Sound: https://www.youtube.com/watch?v=I5U6pMZfxhI

    • How the Doppler effect works: https://www.youtube.com/watch?v=ffg4TOpXZyg

    • Doppler Effect | Science for Kids: https://www.youtube.com/watch?v=QCtwUXpzZoc

    • What is the Doppler Effect? - Science for Kids: https://www.youtube.com/watch?v=ofsHRQnJ8as

    • How do dolphins use echolocation to navigate the deep seas?: https://www.youtube.com/watch?v=CE5tZKFVlto