Acoustics and Wave Mechanics

Vocabulary flashcards covering wave fundamentals, wave measurements, phase relationships, wave types, acoustic behaviors, interference, and resonance from the lecture notes.

Waveform

A graphic representation of the shape of a wave that indicates its characteristics, such as frequency and amplitude.

Periodic Motion

Motion that is repetitive and repeats itself on regular time intervals.

Cycle

The completion of one full repetition of the periodic motion in a waveform.

Frequency ($f$)

The number of cycles per second, measured in Hertz ($\text{Hz}$), which equals $\text{cycles/second}$. It is inversely related to period by $f = \frac{1}{T}$.

Period ($T$)

The amount of time required to complete one cycle ($\text{seconds/cycle}$), typically measured in seconds or milliseconds. It is inversely related to frequency by $T = \frac{1}{f}$.

Pitch

The perceptual correlate (result) of frequency; as frequency increases, pitch increases.

Wavelength ($\lambda$)

The distance in space between two adjacent identical points on a wave. It has an inverse relationship with frequency and a direct relationship with period.

Amplitude ($A$)

The maximum magnitude of a waveform.

Volume

The perceptual correlate of amplitude; as amplitude increases, volume increases.

Phase

The specific position of a wave within its cycle, analogous to counterclockwise locations around a circle spanning from $0^\circ$ to $360^\circ$.

Phase Relationship

The description of the difference between the phases of two periodic waveforms as they cycle through time.

In-Phase Waves

Two waveforms that have the exact same frequency and the same starting phase (e.g., both starting at $0^\circ$).

Out-of-Phase Waves

Two waveforms that share the same frequency but have different starting phases (such as one wave starting at $0^\circ$ and the other at $90^\circ$).

Mechanical Wave

A type of wave that transfers mechanical energy from one molecule to another through a physical medium.

Medium

The matter that occupies a space and enables mechanical waves to travel; can be a solid, liquid, or gas.

Transverse Wave

A mechanical wave in which the particles of the medium oscillate perpendicular to the direction the wave is propagating.

Longitudinal Wave

A mechanical wave, such as a sound wave, in which the particles in the medium oscillate parallel to the direction the wave travels.

Condensation (Compression)

Regions in a longitudinal sound wave where particles bunch closely together, resulting in increased density and increased pressure.

Rarefaction

Regions in a longitudinal sound wave where particles are spread apart, resulting in decreased density and decreased pressure.

Sound Diffraction

The ability of sound waves to bend around obstacles and barriers; longer wavelengths pass over or bend around objects more easily.

Doppler Effect

A shift in the perceived frequency of a sound wave resulting from the movement of the sound source relative to a stationary observer.

Reflection

The phenomenon in which sound waves bounce off hard, slick surfaces like tile, concrete, or hardwood rather than being absorbed.

Reverberation

The persistence of sound caused by sound waves bouncing around within an enclosed space.

Absorption

The dissipation of sound energy as it travels, caused by friction between air molecules or by environmental materials.

Constructive Interference

The superposition that occurs when two in-phase waves combine, causing their magnitudes to add together and increase.

Destructive Interference

The superposition that occurs when out-of-phase waves combine, causing opposite magnitudes to subtract from or cancel each other out.

Beats

Slow periodic amplitude fluctuations produced when two waves with very close frequencies interfere; calculated as $f_{\text{beats}} = f_2 - f_1$.

Helmholtz Resonator

An acoustic resonator developed by Hermann von Helmholtz (1862) containing an acoustic mass ($M_a$) in its neck and acoustic elasticity ($C_a$) in its volume ($V$), functioning analogously to a mechanical mass-and-spring system.