15 sound

1. The Physics of Sound

2. The Nature of Sound SOUND is a longitudinal wave that is created by vibrating objects that is capable of producing a sensation in our auditory system. It is also called pressure wave because it consists of a series of high pressure (compression) and low pressure (rarefaction) regions. The audible range of sound frequency for humans is from 20Hz – 20 000Hz. Sounds with frequencies below 20Hz are called infrasounds and the ones above frequencies of 20 000Hz are called ultrasounds .

3. The Speed of Sound Since sound is a mechanical wave, then its velocity is affected by the kind of medium that it travels through. For every phase of matter, there is a corresponding equation that describes the speed of sound. through air : v = 331 + 0.6T c ( T c is temperature in  C ) (in m/s)

4. Doppler Effect The apparent change in pitch due to the relative motion of the source and/or the observer.

5. Characteristic of Sound Sound may be described by 3 perceptual (as perceived by human senses – auditory) characteristics: pitch , quality , and loudness . These 3 characteristics correspond to 3 physical (scientific) characteristics: frequency , waveform , and intensity .

6. Characteristics of Sound Pitch PITCH refers to the highness or lowness of a sound, and therefore depends on the frequency of the sounding object. It is also related to the wavelength and the energy that it carries. high pitch -- high frequency -- short waves -- high energy low pitch --- low frequency --- long waves --- low energy

7. Characteristics of Sound Loudness This is scientifically described as sound intensity , the greater the intensity, the louder the sound, measured in decibels. Threshold of hearing – 0 db Threshold of pain – 120 db Sound Intensity ( I ) refers to the energy the sound delivers to a unit area of a surface per unit time. Proportional to amplitude Inversely proportional to distance from source

8. Characteristics of Sound Quality QUALITY, a.k.a. timbre , is the property of a tone that distinguishes it from another tone of the same pitch and loudness produced by a different musical instrument. It is described by the kind of waveform that resulted from the impositions of its component frequencies.

9. Sound as a Wave Refraction (bending) – sound bends due to temperature difference Diffraction (scattering) –the sound wave scatters upon passing through an opening Interference (meeting) – could be destructive or constructive e.g. noise and sound cancellation/reinforcement technology Reflection (bouncing) – reflection of sound is called an ECHO, a series or multiple echoes is REVERBERATIONS.

10. SONAR: Sound Navigation and Ranging

11. Altimeter (Altitude Meter)