Sound

My Topic:SoundBy,

U.Meghana

SoundSound is a mechanical wave that is an oscillation of pressure transmitted through a solid, liquid, or gas, composed of frequencies within the range of hearing.

Propagation of sound

The behaviour of sound propagation is generally affected by three things:

• A relationship between density and pressure. This relationship, affected by temperature, determines the speed of sound within the medium.

• The propagation is also affected by the motion of the medium itself. For example, sound moving through wind. Independent of the motion of sound through the medium, if the medium is moving, the sound is further transported.

• The viscosity of the medium also affects the motion of sound waves. It determines the rate at which sound is attenuated. For many media, such as air or water, attenuation due to viscosity is negligible.

Perception of sound

The perception of sound in any organism is limited to a certain range of frequencies. For humans, hearing is normally limited to frequencies between about 20 Hz and 20,000 Hz (20 kHz).The scientific study of human sound perception is known as psychoacoustics.

Pinna

HUMAN EAR

Types Of Sound WavesTwo types of waves:

Longitudinal wavesTransverse wavesLongitudinal sound waves are waves of alternating pressure deviations from the equilibrium pressure, causing local regions of compression and rarefaction. Sound is a longitudinal wave.A transverse wave is a moving wave that consists of oscillations occurring perpendicular (or right angled) to the direction of energy transfer. Light is  a transverse wave.

STUDY OF SOUNDIs known as

ACOUSTICS

Properties of SoundA sound is a vibrationThe vibrating causes the air molecules near the movement to be forced closer. This is called compressionAs the vibration moves on, the density and air pressure becomes lower than normal and is called rarefaction.Pressure wave – longitudinalv = 334 m/s in air at room temperatureVelocity is dependent upon the material

Doppler Effect• The Doppler effect is the change

in frequency of a wave (or other periodic event) for an observer moving relative to its source.

•  The received frequency is higher (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is lower during the recession.

Change in pitch due to motion.

Speed Of SoundSound travels faster in warm water than in cold water.By measuring the time it takes for sound to travel a known distance through the ocean the average temperature of the water can be calculated = ATOC (acoustic thermometry of ocean climate).

Intensity• Also called LOUDNESS• Amount of energy• Depends on the amplitude of sound waves. (amplifier)

Large Amp. = Loud sound

Small Amp. = Soft sound

•Sound waves reflecting from hard surfaces•Ex.: Multiple echo resulting from the direct sound and the reflected sound

Reverberation vs. Echo

Applications

Sonar • Sonar (originally

an acronym for SOund Navigation And Ranging) is a technique that uses sound propagation to navigate, communicate with or detect objects on or under the surface of the water, such as other vessels.

• Used to locate underwater objects and distances.

UltrasoundsUltrasound can be used to create internal images of the human body

Ex. Pregnant woman gets a “picture” of her unborn baby

Tuning Fork creating a sound wave

Guitar strings creating a sound wave

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