Properties of sound waves

1. Properties of sound waves Coach Medford Building Science Champions

2. IN thought • How does sound reflection help radar personnel?

3. Objectives • Describe how amplitude and energy are related • Explain the relationship among frequency, pitch and wavelength • Justify how sound is recognized through various sources

4. Key Terms • Amplitude • Intensity • Wavelength • Frequency • Pitch • Doppler effect • Interference • Resonance

5. Energy of sound waves • The amount of energy a sound wave carries depends on the amount of energy that causes the original vibration • Amplitude – is the maximum distance the particles in a medium move from their rest positions as the waves passes through the medium, if your mother ask you to turn down the radio, you are turning down the amplitude • As the energy of a wave increases, its amplitude increases • As the energy of a wave decreases, its amplitude decreases • AMPLITUDE SHOWS ENERGY

6. Amplitude, intensity and loudness • Intensity - the amount of wave energy that passes through a square meter of space in one second • When amplitude decreases, intensity decreases • Loudness is the way a person perceives the amplitude of a sound wave • The unit decibel describes how loud a sound is • The louder a sound is, the shorter amount of time you can listen without hearing loss

7. Describing Sound Waves • A sound wave consist of one compression and one rarefaction • Wavelength – distance between a point on one wave and the same point on the next wave • Frequency – is the number of waves that pass by a point each second • The unit for frequency is the hertz (Hz), each of which is one vibration per second

8. Pitch • Pitch – how high or low a sound is • Higher frequency produces higher pitch • Lower frequency produces lower pitch • Frequencies higher than sounds that humans can perceive are ultrasounds • The Doppler affect is the change of pitch when a sound source is moving in relation to an observer

9. Sound Interference • Interference – when waves that overlap combine, forming a new wave • When a compression meets another compression, it is called constructive interference, and the wave formed has higher intensity and greater amplitude than the original wave • When a compression meets a rarefaction, it is called destructive interference, and the waves cancel each other out

10. Beats • When waves of slightly different pitch interfere, beats occur • Beats are the repeating increases and decreases in amplitude • The difference in frequency determines how often a beats will occur

11. Fundamental and overtones • Objects vibrate with a fundamental and overtone • The lowest frequency at which a material naturally vibrates is its fundamental • The highest frequency at which a material vibrates is called its overtone.

12. Ultrasound • Ultrasound are sounds that humans cannot hear • Sonograms are used to check the development of unborn babies inside the mother’s body • Acoustic engineers do not have to worry about ultrasound because humans cannot hear it

13. Review • The higher the frequency the lower the wavelength the higher the pitch • When a wave has more energy its amplitude is greater • Ears help you determine sources of sound • The Doppler effect is caused by the movement of the source of sound in relation to an observer

14. References • Anderson, M. et all (2012) Physical Science. McGraw-Hill: Columbus • Frank, D.V et al (2001). Physical Science. Prentice Hall: New Jersey