SLHS 2010 Exam 2 Study Guid
Study Guide
Key Concepts & Definitions:
Sound & Simple Harmonic Motion (SHM)
Sound: A vibration that travels through a medium (air, water, solids) in the form of pressure waves.
Simple Harmonic Motion (SHM): A repetitive movement back and forth through an equilibrium position, such as a pendulum or tuning fork.
Examples of SHM:
Pendulum: Swings back and forth due to gravity and inertia.
Mass on a Spring: Moves up and down due to elasticity and inertia.
Tuning Fork: Vibrates to create sound waves.
Vibration of an Air Mass: Produces sound through compressions and rarefactions.
Key Physics Concepts:
Inertia: The tendency of an object to resist changes in motion.
Potential Energy: Stored energy due to position.
Kinetic Energy: Energy of motion.
Velocity: Speed with direction.
Gravity: Force pulling objects toward Earth.
Elasticity: Ability of an object to return to its original shape.
Wave Properties
Compression & Rarefaction: Alternating high (compression) and low (rarefaction) pressure areas in a sound wave.
Transmission of Sound in Space: Sound requires a medium and cannot travel in a vacuum.
Types of Waves:
Transverse Wave: Particles move perpendicular to wave direction (e.g., water waves).
Longitudinal Wave: Particles move parallel to wave direction (e.g., sound waves).
Surface Wave: Combination of transverse and longitudinal motion.
Waveform: A graphical representation of a sound wave over time, showing amplitude variations.
Frequency & Period
Frequency: The number of cycles per second, measured in Hertz (Hz).
Human Hearing Range: 20 Hz to 20,000 Hz.
Octave: Doubling (up) or halving (down) a frequency.
Period: The time for one complete cycle (T = 1/Frequency).
Wavelength: Distance a wave travels in one cycle (Wavelength = Speed of Sound / Frequency).
Effect of Temperature: Higher temperatures increase the speed of sound due to faster-moving air molecules.
Amplitude & Decibels
Amplitude: The height of a sound wave, related to loudness.
Displacement: Change in position from equilibrium.
Instantaneous Amplitude: The amplitude at a specific time.
Peak Amplitude: The maximum displacement from equilibrium.
Peak-to-Peak Amplitude: The total height from the highest to the lowest point of the wave.
Force vs. Pressure:
Force: Push or pull on an object.
Pressure: Force per unit area, used to measure sound intensity.
Decibel (dB): A logarithmic unit to measure sound intensity.
Formula for dB SPL: dB SPL = 20 * log (Observed Pressure / Reference Pressure).
Wave Behavior & Resonance
Damping: Decrease in amplitude over time due to energy loss.
Phase: The position of a point in time on a waveform cycle, measured in degrees.
Interference:
Constructive Interference: Waves combine to increase amplitude.
Destructive Interference: Waves combine to cancel each other.
Complex Waves: Formed by combining multiple frequencies.
Harmonics & Fourier Series:
Fundamental Frequency: The lowest frequency of a complex wave.
Harmonics: Integer multiples of the fundamental frequency.
Fourier Series: Decomposition of a complex wave into sine waves.
Resonance: An object vibrating at its preferred frequency with increased amplitude.
Mechanical vs. Acoustic Resonance:
Mechanical Resonance: Physical objects vibrating at their natural frequency.
Acoustic Resonance: Sound waves resonating in a medium, like air in a tube.
Filters & Acoustic Resonance
Resonance in Tubes:
Open Tube: Resonates at wavelengths where the tube length is half the wavelength.
Closed Tube: Resonates at wavelengths where the tube length is a quarter of the wavelength.
Standing Waves: Waves that remain stationary due to interference.
Nodes & Antinodes:
Nodes: Points of no displacement.
Antinodes: Points of maximum displacement.
Filters: Devices that remove or emphasize certain frequencies.
Formulas to Know:
Period (T) = 1 / Frequency (F)
Wavelength (λ) = Speed of Sound (c) / Frequency (F)
dB SPL = 20 * log (Pressure / Reference Pressure)
Octave Calculations:
One octave above: Frequency * 2
One octave below: Frequency / 2