Physics - Sound + Waves

Wave Speed Formula

v = f λ

Wavelength Equation

λ = v/f

Frequency Equation

f = v/λ

Period Equation

T = 1/f

Open Tube Wavelength

λ = 2L/n

Closed Tube Wavelength

λ = 4L/n (only odd n = 1,3,5…)

Shorter Tube

Higher frequency/pitch

Transverse

Particles move perpendicular to wave direction. Example

Longitudinal

Particles move parallel to wave direction. Example

Mechanical Wave

Requires a medium to travel.

Wavelength (λ)

Distance between repeating points (crest→crest, compression→compression).

Frequency (f)

Number of waves per second (Hz). Determines pitch.

Amplitude (A)

Maximum displacement of a wave. Determines loudness.

Reflection (fixed end)

Wave inverts.

Reflection (free end)

Wave does not invert.

Transmitted Wave

Wave passes into new medium, does not invert, may change speed/wavelength.

Superposition

Two waves overlap → amplitudes combine.

Constructive Interference

Waves add → amplitude increases.

Destructive Interference

Waves subtract → amplitude decreases.

Memory Trick

"Fixed flips, free stays".

Speed of Sound

Solids > Liquids > Gases.

Pitch

Determined by frequency.

Loudness

Determined by amplitude.

Guitar/String Instruments

Shorter/tighter string → frequency increases → pitch increases; Thicker string → frequency decreases → pitch decreases.

Node

Point of no movement in standing wave.

Antinode

Point of maximum movement.

Standing Wave

Appears stationary due to interference of two opposite waves.

Resonance

Object vibrates at natural frequency → amplitude increases.

Doppler Effect

Change in frequency/pitch due to relative motion between source and observer.

Doppler Approaching

pitch increases.

Doppler Receding

pitch decreases.

Open Tube

Antinodes at both ends.

Closed Tube

Node at closed end, antinode at open end.

Outer Ear

Collects sound waves.

Middle Ear

Eardrum + ossicles → amplifies vibrations.

Inner Ear

Cochlea converts vibrations into electrical signals.

Auditory Nerve

Sends signals to brain for interpretation.

How Hearing Works

Sound travels outer ear → middle ear → inner ear → brain.

Transmitted Wave into Less Dense Medium

amplitude increases, speed increases, no inversion.

Reflected Wave at Lighter Medium

no inversion.

Sound Properties

Mechanical, longitudinal, can travel in any direction.