1. 1 Chapter 15 Objectives: 1) Explain a sound wave in terms of wave type and classification. 2) Describe a medium’s characteristics that affect the speed of sound waves traveling through it. What is the average speed of sound in air? 3) Define pitch. Which wave characteristic is related to pitch and how? 4)Know the frequencies of the human hearing range. 5) Explain loudness in regard to a sound wave.

2. 2 6) Define Doppler Effect. Be able to explain the changes in the Doppler Effect as a source of sound waves changes velocity. 7) Define Resonance and explain how it relates to natural frequency. 8) Know how resonance is achieved in wind instruments and stringed instruments and the harmonics possible for each. 9) Apply the equations for harmonics and instrument lengths to solve for wavelength, frequency, and velocity.

3. 3 Properties of Sound Sound is in the classification of a _______________ wave. – a disturbance that travels through a medium – Bell jar under vacuum. Bell jar under vacuum. Sound is a type of________________ wave – the motion of the individual particles of the medium is in a direction which is parallel to the direction of energy transfer.

4. 4 What Affects Sound Velocity? Sound waves move through the air because a vibrating source produces regular air pressure variations. Sound can travel through solids, liquids, and gases. The speed of sound depends on the medium’s particle _____________, ____________, and ___________. Helium balloon example: The change in the media (air to helium) caused the particles to move ______________. Table 15-1 pg. 405

5. 5 What Affects Sound Velocity? Sound travels ________________ in solids and liquids than in gases. Find the wavelength in water at 25°C of a 30-Hz sound wave from a whale.

6. 6 Behavior of Sound Waves Sound waves have velocity, frequency, and wavelength like all other waves. Sound waves _______________ and _________________ off boundaries like all other waves. Bats use this reflection (Echolocation) to hunt down insects. -Bats send out a high frequency sound (it is too dark to see an insect) -From the echo they can determine the insect’s ______________, ____________, and which direction it is traveling. Bat using EcholocationBat using Ears

7. 7 ______________ depends on the frequency we hear. – Pitch is the highness or lowness of a sound wave (A,B,C,D,E,F,G) – 20Hz – 16,000Hz is the human ear range. – As frequency ____________, pitch _____________. (Think tuning forks) The human ear is a detector that receives _____________ and converts them into electrical impulses. The Human Ear The ear detects sound waves over a wide range of frequencies.

8. 8 Perceiving Sound If the human ear can perceive frequencies between 20Hz and 16,000Hz, in 20°C air, what wavelengths correspond to these frequencies?

9. 9 Perceiving Sound ______________: Sound intensity as sensed by the ear and interpreted by the brain. Depends mainly on the wave’s amplitude. Loudness is known as ____________________. Units for Loudness are _________. Figure 15-4, Pg. 406

10. 10 The source emits the same _____________________. Because the distance between the source of sound and the observer is changing, the same number of waves have to fit in a larger space. Thus, the frequency is perceived to change. Doppler Effect __________________: The change in frequency of sound caused by movement of either the source, the detector, or both. (Doppler Effect Example)Doppler Effect Example Bats use this to detect if an insect is moving toward or away from it.

11. 11 Doppler Effect v source < v sound v source = v sound v source > v sound Sonic Boom

12. 12 Sources of Sound Sound is produced by a vibrating object. Vibrating object – Particle motion - Pressure oscillations in the air Examples Cymbals- smashing cymbals together, vibrates the metal Human Voice - air rush through lungs, vibrates vocal chords Trumpet- lips of the performer vibrates Clarinet- blow air across reed, vibrates the reed Flute- blow air across the opening, air moving past the opening sets the column of air in the instrument into vibration Guitar- plucking a string, vibrates the string

13. 13 Resonance ___________________: small forces are applied at regular intervals to a vibrating or oscillating object and the amplitude of the vibrations increases. The ______________ of the air column determine the frequencies of the vibrating air that will be set into resonance. – In an instrument like a trombone, changing the length of the column of vibrating air, varies the pitch of the instrument. In other words, the mouthpiece makes various frequencies, but the resonating air column chooses which frequencies will be amplified. Tacoma Bridge _______________________: Fundamental frequency; the frequency at which an object would normally oscillate at (vibrations) when disturbed.

14. 14 Wave hits the water surface and is reflected back up to the tuning fork at the same moment the fork produces another high-pressure wave. This reinforcement of waves produces a standing wave, and _____________ is achieved. Closed Pipe Resonator Tuning fork vibrates producing a sound wave. This wave of alternate high- and low- pressure variations moves down the air column.

15. 15 Closed Pipe Resonator l = length of the pipe l = 1/4 λ l = 3/4 λ l = 5/4 λ A closed pipe resonator only vibrates at odd ___________. Harmonics: Multiples of the first resonance frequency. *n is the harmonic value

16. 16 Open Pipe Resonator l = __ λ 1 st resonance condition or 1 st harmonic l = __ λ *n is the harmonic value

17. 17 Open Pipe Resonator What length of open ended pipe will produce the 1 st harmonic of a 512Hz tuning fork with the speed of sound being 340 m/s?

18. 18 Resonance on Strings *n is the harmonic value

19. 19 A guitar string is 65cm in length and is tuned to produce a 1 st harmonic frequency of 196Hz. a) What is the speed of the wave on the string? b) What are the frequencies of the next 2 harmonics? Resonance on Strings