C HAPTER 16 S OUND Nuay, Emmanuel Barquila, Rae Angelo Delos Reyes, Remjun

I. The Nature of Waves A. Wave ‘1. Transverse Wave 2. Longitudinal Wave II. Periodic Waves A. Amplitude B. Wavelength C. Period D. Frequency III. The Nature of Sound A. Sound 1. Condensation 2. Rarefaction

B. The Frequency of a Sound Wave 1. Pure Tone a. High – pitched sound b. Low – pitched sound 2. Frequency a. Infrasonic Frequency b. Ultrasonic Frequency C. The Pressure Amplitude 1. Pressure Amplitude 2. Loudness IV. The Speed of Sound

V. Sound Intensity A. Power B. Sound Intensity VI. Decibels VII. The Doppler Effect

T HE N ATURE OF W AVES A wave is a traveling disturbance and carries energy from place to place. In a transverse wave, the disturbance occurs perpendicular to the direction of travel of wave. In a longitudinal wave, the disturbance occurs parallel to the line along which the wave travels.

P ERIODIC W AVES A periodic wave consists of cycles or patterns that are produced over and over again by the source of the wave. The amplitude of the wave is the maximum excursion of a particle of the medium from the particle’s undisturbed position. The wavelength is the distance along the length of the wave between two successive equivalent points, such as two crests or two troughs.

The period is the time required for the wave to travel a distance of one wavelength. The frequency is the number of wave cycles per second that passes an observer and is the reciprocal of the period (in seconds).

T HE N ATURE OF S OUND Sound is a longitudinal wave that can be created only in a medium; it cannot exist in a vacuum. Each cycle of a sound wave includes one; Condensation a region of greater than normal pressure Rarefaction a region of less than normal pressure

The Frequency of a Sound Wave Pure tone a sound wave with a single frequency High - pitched sound a pure tone with a large (high) frequency. a piccolo instrument with a high - pitched sound

Low – pitched sound a pure tone with a small (low) frequency. a tuba instrument with a low pitched - sound

Frequency Infrasonic Frequency frequencies less than 20 kHz Ultrasonic Frequency frequencies greater than 20 kHz

T HE S PEED OF S OUND Sound travels through gases, liquids, and solids at considerably different speeds. SubstanceSpeed (m/s) Gases Air (0°C)311 Air (20°C)343 Carbon dioxide (0°C)259 Oxygen (0°C)316 Helium (0°C)965

SubstanceSpeed (m/s) Liquids Chloroform (20°C)1004 Ethyl alcohol (20°C)1162 Mercury (20°C)1450 Fresh water (20°C)1482 Seawater (20°C)1522 Solids Copper5010 Glass (Pyrex)5640 Lead1960 Steel5960

S OUND I NTENSITY Power The amount of energy transported per second by a sound wave is called the power of the wave and is measured in SI units of joules per second (J/s) or watts (W). Sound Intensity The sound intensity I is defined as the sound power P that passes perpendicularly through a surface divided by the area A of the surface.

D ECIBELS The decibel (dB) is a measurement unit when comparing two sound intensities. The simplest method of comparison would be to compute the ration of the intensities.

T HE D OPPLER E FFECT The Doppler Effect is the change in frequency detected by an observer because the source and the observer have different with respect to the medium of sound propagation. 1. Velocity of Sound Source 2. Velocity of Observer Requirement: They must be different. Sound Wave 1.Wavelength 2. Frequency. The Doppler Effect