Key Terms WavelengthCompressions WavelengthCompressions FrequencyRarefactions FrequencyRarefactions PitchNodes PitchNodes HarmonicAntinodes HarmonicAntinodes ResonanceLoops ResonanceLoops Standing wave Standing wave Timbre Timbre

Sound Waves are Longitudinal Waves

Also known as Compressional Waves Particles vibrate parallel to the direction in which the wave is propagated. Particles vibrate parallel to the direction in which the wave is propagated.

Compressions and Rarefactions Compressions: areas of high density Compressions: areas of high density Rarefactions: areas of low density Rarefactions: areas of low density

Frequency and Pitch Pitch Pitch –The way in which humans perceive frequency. –Frequency is related to pitch. Frequency Frequency –Vibrations per second –Higher frequency waves are perceived has higher pitches. –Lower frequencies are perceived as lower pitches.

Wavelength Frequency and Pitch Wavelength Wavelength –The length of one full cycle Higher frequencies produce shorter wavelengths. Higher frequencies produce shorter wavelengths. Shorter wavelengths produce higher pitches. Shorter wavelengths produce higher pitches.

Can you make a statement that relates frequency, wavelength and pitch? Can you make a statement that relates frequency, wavelength and pitch?

How Does a Vibrating Sting Produce Sound?

How? As the string moves back and forth areas of high and lower pressure are created. As the string moves back and forth areas of high and lower pressure are created. The vibrating air molecules create a pulse that moves away from the string. The vibrating air molecules create a pulse that moves away from the string. Narrower strings produce _________ pitches because they vibrate ________. Narrower strings produce _________ pitches because they vibrate ________. –Higher –Faster

Resonance Resonance occurs when natural vibrations overlap and reinforce each other. Resonance occurs when natural vibrations overlap and reinforce each other. –Pushing a child on a swing to create the Maximum amplitude. –Tacoma Narrows bridge –The hollow box of an acoustic instrument

Music Versus Noise Sounds that are pleasing to the ear have a whole number mathematical relationship. Sounds that are pleasing to the ear have a whole number mathematical relationship. –The tuba tends to vibrate at a set of frequencies that are whole number ratios.  Flute - 200Hz Tuba – 200, 400, 600, 800, 1000 Hz –Noise is created when the object vibrate with frequencies that have no apparent mathematical relationship.  Dropped pencil – 197,211,217,219,287,311,329,299,407 Hz

Exit Ticket Questions 1. What happens to the wavelength of a wave when the frequency increases? 1. What happens to the wavelength of a wave when the frequency increases? 2. How does resonance increase the volume of a sound? 2. How does resonance increase the volume of a sound? 3. Why does an F sharp have a different tone when it is played on a piano than it does on a flute? 3. Why does an F sharp have a different tone when it is played on a piano than it does on a flute? 5. Why are some sounds pleasing and others considered noise? 5. Why are some sounds pleasing and others considered noise?

Why does middle C sound different on a piano versus a flute? Timbre Timbre –The quality of a sound. –Combination of natural frequencies  The Flute tends to vibrate at a single frequency while the tuba vibrates with a set of overlapping and complex frequencies. Factors affect wavelength or the speed of the wave. Factors affect wavelength or the speed of the wave. –Properties of the medium  Composition of the material  Density  Tension  Length of the vibrating string or column of air.  Temperature –Since speed and wavelength affect frequency, these factors affect the sound that we hear.

Resonance and Standing Waves All objects have a set of frequencies with which they naturally vibrate. All objects have a set of frequencies with which they naturally vibrate. These natural frequencies are associated with what are called standing wave patterns. These natural frequencies are associated with what are called standing wave patterns. –Standing wave patterns are created when waves reflect back on themselves within a medium. –They are called standing wave patterns because when the reflect back on themselves they appear to be standing still. –These standing wave patterns occur at specific frequencies are known has harmonic frequencies.

Nodes and Antinodes Anitnodes and nodes are created when a wave reflects back on itself. Anitnodes and nodes are created when a wave reflects back on itself. Nodes Nodes –Areas of zero displacement. Antinodes –Areas of maximum displacement. Antinodes and nodes are a result of total destructive interference Antinodes and nodes are a result of total destructive interference

Answers to Exit Ticket Questions

First Harmonic or Fundamental Frequency

Second Harmonic

Third Harmonic

Check your understanding Suppose that a string is 1.2 meters long and vibrates in the first, second and third harmonic standing wave patterns. Determine the wavelength of the waves for each of the three patterns. 1 st harmonic 2.4 m2 nd harmonic 1.2 m3 rd harmonic 0.8 m 2. The string at the right is 1.5 meters long and is vibrating as the first harmonic. The string vibrates up and down with 33 complete vibrational cycles in 10 seconds. Determine the frequency, period, wavelength and speed for this wave. Frequency 3.3 Hz Period seconds Wavelength 3 meters Velocity 9.9 m/s

3. The string at the right is 6.0 meters long and is vibrating as the third harmonic. The string vibrates up and down with 45 complete vibrational cycles in 10 seconds. Determine the frequency, period, wavelength and speed for this wave. Frequency 4.5 Hz Period 0.22 seconds Wavelength 4 meters Velocity 18 m/s