Unit: Waves Topic(s): Sound and Music Learning Goals: Describe Sound in terms of energy transfer Explain how amplitude of a sound wave relates to the energy of the wave (via real world examples) D emonstrate the Doppler effect qualitatively or quantitatively (via wave front diagram) Predict property of standing waves that are confined to a region Calculate wavelength and frequencies associated with possible harmonics for musical instruments

Sound Facts Mechanical Wave Longitudinal Wave Propagate from source in 3-D Consists of alternating regions of compression (high pressure) and rarefaction (low pressure) Speed of sound varies by medium (p329)

Sound Facts Part 2 Frequency and volume (relative intensity dB) are the deciding factors if you can hear something. Audible frequency range 20Hz-20kHz Age effects ability to hear frequency Frequency determines pitch (notes) Frequency Generator Demo

Energy of Sound Sound energy is the result of energy transformation. (ex: Speaker converts electrical energy to sound energy). The power (or loudness) is related to how quickly the energy is converted (P=energy/time) Since sound waves are pressure waves, their amplitude is related to their pressure and energy. These pressure waves can cause other substances to vibrate, and if the materials cannot handle the level of vibration there may be damage.

Physics of Music Non-conventional instrument categories Tension and physical characteristics of strings matter “Air” instruments use valves and slides to change L. Embouchure can change things too. Music scales use harmonics (aka overtones)

Standing waves “in or on” an instrument correspond to the harmonic series for that instrument (or object) Forced vibration (resonance) v=f  – Certain wavelengths are allowed based on length of vibrating medium – v is the speed of the wave in the medium (doesn’t have to be speed of sound) – f would be the pitch of the sound (note)

String Instruments Standing waves have nodes on both ends (as the ends are fixed) Tension and string composition impact the speed of the wave on the string which, in turn impacts the pitch. All the harmonics are possible

Open at both end (air instruments) Example: Flute Woodwinds and many brass instruments do not fit in this category, because once the musician places their mouth over the end of the instrument, the end becomes closed (fixed). Standing wave has an antinodes at each end All the harmonics are possible

Closed at one end (air instruments) Majority of woodwind and brass instruments Closed at mouthpiece (node) Open at end (antinode). Only odd harmonics stm/physics/waves/standingWav es/standingWaves.html

Frequency of wave on string or in air n is the harmonic (n=1 is first harmonic or fundamental frequency) v is the velocity of the wave in the medium L is length of the medium

Doppler Effect Apparent change in frequency (pitch)of sound due to a moving source or detector You can hear this in a passing ambulance. Radar makes use of Doppler Effect Astronomers use Doppler Effect with light to determine if objects are moving towards/away from us.