Speed of Sound

1. Speed of Sound • The speed of sound is 346 m/s at room temperature. • The speed of sound depends on elasticity, density, and temperature of the medium.

2. Properties of Sound • Intensity of a sound wave is the amount of energy that a wave carries per second through a unit area. • Loudness describes what you actually hear. • A sound wave of greater intensity generally sound louder.

3. Sound Loudness • The loudness of sound is measured in decibels. • Threshold of hearing is at 0 decibels. • Sound louder than 120 decibels can cause pain and permanent damage.

4. Frequency & Pitch • Frequency is the number of sound waves that pass a given point in a given amount of time. • Human hearing is between 20 Hz and 20,000 Hz. • Ultrasound is sound waves above the normal human hearing range.

5. Frequency & Pitch • Infrasound are sound waves that are below the normal range of human hearing. • Pitch of a sound is a description of how high or low the sound seems to a person. • Pitch of a sound that you hear depends on the frequency of the sound wave.

6. :10 As the frequency of a sound wave increases . . . . • Pitch increases. • Pitch decreases. • Pitch stays the same. • HELP! I don’t get it!

7. Resonance • Resonance occurs when the frequency of the sound waves and the natural frequency of the objects are the same. • If resonance occurs in an object that is not flexible, the object will break (shattering of a glass).

8. The Doppler Effect • The apparent change in frequency as a wave source moves in relation to the listener is called the Doppler Effect. • As sound source moves toward the listener, the waves reach the listener with a higher frequency. • The pitch appears to increase because of the Doppler effect.

9. :10 According to the Doppler Effect, as a sound is approaching you, . . . . • Wavelength increases and frequency decreases. • Wavelength decreases and frequency increases. • Wavelength increases and frequency increases. • Wavelength decreases and frequency decreases.

10. Combining Sound Waves • Timbre describes the quality of the sound you hear. • The blending of the fundamental tone and the overtones makes up the characteristic sound quality, or timbre, of a particular sound.

11. Music • Music is a set of tones combined in ways that are pleasing to the ear. • Types of instruments: • Strings • Brass • Woodwinds • Percussion

12. Noise • Noise has no pleasing timbre and no identifiable pitch.

13. Interference of Sound Waves • Interference occurs when two or more sound waves interact. • Acoustics describe how well sound can be heard in a particular room or hall. • Repeated change in loudness are called beats.

14. :10 What do we call sound that is pleasing to the ear? • music • noise • timbre • acoustic

15. Hearing Sound • The outer ear funnels sound waves, the middle ear transmits the waves inward, and the inner ear converts the sound waves into a form that your brain can understand.

16. Outer Ear • The outer ear funnels the sound waves to the ear canal. • The sound travels down the ear canal and vibrates the eardrum.

17. Middle Ear • The middle ear contains three small bones: hammer, anvil and stirrup. • The vibrations travel from the eardrum to the hammer, then the anvil and finally the stirrup.

18. Inner Ear • The stirrup vibrates the cochlea. • The cochlea contains fluid and tiny hairs that are stimulated by the vibrations. • The stimulations of the tiny hairs send messages to the brain.

19. :10 Which of the following bones are found in the ear? • anvil • hammer • stirrup • All three

20. Hearing Loss • Hearing loss is caused by: • Injury • Infection • Aging (like me?)

21. Facts: • More than 40 million Americans have hearing loss. • Approximately 40% of the hearing-impaired are under age 65. • About 2 million children under age 18 are hearing-impaired in the U.S. • Minor decreases in hearing, especially of higher frequencies, are normal after age 20. • Some form of hearing loss affects 1 out of 5 people by age 55.

22. Facts: • One-third of Americans between the ages of 65 and 74 - and one-half of those age 85 and older - have some form of hearing loss. • Hearing loss is the third leading chronic disability, following arthritis and high blood pressure. • Between 7 and 10 million people in American industry have noise-induced hearing loss, virtually all of which was preventable. • About 15% of college graduates have a level of hearing loss equal to or greater than their parents; a significant cause is listening to loud music.

23. Facts: • In the U.S., 12 million people have hearing aids. • Of the 12 million with hearing aids, only 6 million actually wear them eight hours a day, seven days a week.

24. Application of Sound • An echo is a reflected sound wave. • Some surfaces absorb sound waves. • Other surfaces reflect sound waves

25. Sonar • Sonar is a system of detecting reflected sound waves. • Sonar stands for sound navigation and ranging. • A sonar device measures the time it takes to detect the reflected sound waves.

26. Ultrasound • Ultrasonic frequency is sound waves above 20,000 Hz. • Echolocation is the use of sound waves to determine distance or to locate objects. • Bats use echolocation to navigate and to find food.

27. Ultrasound (continue) • Ultrasound produce pictures called sonogram. • Doctors use ultrasound to look inside the human body and to diagnose and treat medical conditions. • Ultrasound is used for focusing cameras, brushing teeth and cleaning jewelry.

28. Test • This Friday, December 18th. • Covers all of sound waves in chapters 15 & 16.

29. Review Questions • What type of wave is sound? • (longitudinal) • What are three factors that affect the speed of sound? • (elasticity, density & temperature) • What are the three bones in the middle ear? • (hammer, anvil & stirrup) • Is sound faster in warmer or cooler temperatures? • (warmer)

30. Review Questions • Is sound faster in elastic material or material that is not elastic? • (elastic) • Is sound faster in less dense or more dense medium? • (less dense) • What does the stirrup shake in the middle ear? • (cochlea) • What does sonar stand for? • (sound navigating and ranging)

31. Review Questions • How do bats navigate? • (echolocation) • What effect describes an increasing pitch as a loud noise is approaching and decreasing pitch as a loud noise is moving away? • (Doppler Effect) • What is the property of sound that is described as the amount of energy that passes by a point each second? • (intensity) • How loud or soft noise is appears to be is known as ___________. • (pitch)

32. Review Questions • What you hear is known as _______________. • (loudness) • Sound is measured in ________________. • (decibels) • Sound waves with frequencies below the human range of hearing is known as _______________. • (infrasound) • Sound waves with frequencies above the human range of hearing is known as _______________. • (ultrasound)

33. Review Questions • When the frequency of an object and the natural frequency are the same, it is known as _______________. • (resonance) • _______________ describes the quality of sound. • (timbre) • What group of instrument vibrates the lips to produce sound? • (brass) • What group of instruments vibrates a reed to produce sound? • (wood-wind)

34. Review Questions • What group of instruments produces sound by rubbing, plucking or striking a string? • (string) • What group of instruments produces sound by being struck? • (percussions) • Sound with no identifiable pitch and unpleasing to the ear is known as _______________. • (noise) • Sound pleasing to the ear with an identifiable pitch is known as _______________. • (music)

35. Review Questions • _______________ describes how well sound can be heard in a particular room. • (acoustics).