CHAPTER 16

SOUND

Nuay, Emmanuel

Barquila, Rae Angelo

Delos Reyes, Remjun

I. The Nature of WavesA. Wave

‘ 1. Transverse Wave2. Longitudinal Wave

II. Periodic WavesA. AmplitudeB. WavelengthC. PeriodD. Frequency

III. The Nature of SoundA. Sound

1. Condensation2. 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

THE NATURE OF WAVES

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.

PERIODIC WAVES

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).

THE NATURE OF SOUND

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 pressureRarefaction 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

THE SPEED OF SOUND

Sound travels through gases, liquids, and solids at considerably different speeds.

Substance Speed (m/s)

Gases

Air (0°C) 311

Air (20°C) 343

Carbon dioxide (0°C) 259

Oxygen (0°C) 316

Helium (0°C) 965

Substance Speed (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

Copper 5010

Glass (Pyrex) 5640

Lead 1960

Steel 5960

SOUND INTENSITY

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.

DECIBELS

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.

THE DOPPLER EFFECT

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. Wavelength2. Frequency

.The Doppler Effect