PHY 1020 – Chapter 7: Waves, UFOs, Earthquakes, and Music

A set of vocabulary flashcards summarizing essential terms and formulas from the lecture on waves, sound phenomena, seismic activity, and water waves.

Wave

A disturbance or oscillation that transfers energy through space and matter.

Amplitude (y)

The maximum displacement or density variation of a wave from its rest position.

Wavelength (λ)

The spatial length of one complete cycle of a wave, measured peak-to-peak or trough-to-trough.

Period (T)

Time required for one wavelength to pass a point; T = λ / v.

Frequency (f)

Number of wavelengths passing a point per second; f = v / λ.

Longitudinal Wave

A wave in which particle displacement is parallel to the direction of energy transfer (e.g., sound, P-waves).

Transverse Wave

A wave in which particle displacement is perpendicular to the direction of energy transfer (e.g., light, S-waves).

Superposition Principle

When two or more waves overlap, the resultant displacement equals the vector sum of individual displacements.

Constructive Interference

Superposition that increases amplitude because wave crests coincide with crests (or troughs with troughs).

Destructive Interference

Superposition that decreases amplitude because wave crests coincide with troughs.

Huygens Principle

Every point on a wavefront behaves as a source of secondary wavelets; spread S = (λ R) / D.

Pitch

Perceived highness or lowness of a sound that rises with increasing frequency.

Sound Wave

A longitudinal compression wave of molecules that vibrates the eardrum; travels faster in stiffer materials.

Beat Frequency (fB)

The absolute difference between two close frequencies: fB = |f2 – f1|.

Decibel (dB)

Logarithmic unit of sound intensity level: I[dB] = 10 log10(I / I0).

Threshold of Hearing (I0)

Reference intensity 1.0 × 10⁻¹² W/m² (0 dB).

Threshold of Pain

Sound intensity level around 140 dB where hearing becomes painful.

Doppler Effect

Shift in observed frequency due to relative motion between source and observer.

SOFAR Channel

Ocean depth layer where sound speed is minimal, guiding low-frequency waves over thousands of miles.

Primary (P) Wave

Longitudinal seismic wave that arrives first during an earthquake.

Secondary (S) Wave

Transverse seismic wave that arrives second during an earthquake.

Long (L) Wave

Surface seismic wave with both transverse and longitudinal motion; arrives last.

Earthquake Magnitude (M)

Logarithmic measure of amplitude relative to reference: M = log10(A / A0(d)).

Shallow-Water Wave

Water wave with wavelength much greater than depth (λ > 20 D); strongly affected by seafloor.

Deep-Water Wave

Water wave with wavelength much smaller than twice the depth (λ < 2 D); unaffected by seafloor.

Intermediate-Water Wave

Wave whose wavelength and depth are comparable; partially interacts with seafloor.

Tsunami

Long-wavelength ocean wave, often seismic-generated, that can travel 1000 mi and arrive at ~386 mph.

Wave Velocity (v)

Speed at which a wave crest travels; v = λ / T = f λ.

Compression Wave

Another term for longitudinal wave where particles compress and rarefy along travel direction.

Shear Wave

Another term for transverse wave where particles move perpendicular to travel direction.