The Natureof Sound Waves

by

Rifki Irawan

Sound WavesPropagation of Waves

Transmission of sound through a

medium

Sound Waves

Propagation of WavesTransmission of sound through a medium

Sound WavesSound Waves• Sound is a wave which is created by vibrating objects

and propagated through a medium from one location to another .

• Sound waves are produced by the vibration of some objects.

• Sound wave is a disturbance which is transported through a medium via the mechanism of particle-to-particle interaction.

• Sound wave is characterized as a mechanical wave.

Propagation of WavesPropagation of Waves• Sound waves are produced when a vibrating object

alternately pushes and pulls on the air adjacent to it, thus causing small but rapid changes in the air pressure.

layers of air

prongs are stationary

prongs move outwards

compressed

• When the prongs move outwards, layers of air are pushed close together so that compression of the air particles is formed.

• This disturbance of air layers is then passed from particle to particle, causing the compression to move outwards.

rarefied

prongs move inwards

• When the prongs move inwards, the air layers are pulled apart, causing a decompression or rarefaction of the air particles.

• When the prongs move outwards again, the second compression forces the previous rarefaction away.

λ

compression( high pressure )

rarefaction( low pressure )

direction of sound waves

• A series of compression (high pressure regions) and rarefaction (low pressure regions) move away from the tunning fork at the speed of sound.

• However, the air particles themselves just vibrate back and forth from their original positions.

prongs keep on vibrating

Transmission of Sound through a Medium• Sound waves need a medium for transmission.

• Sound cannot propagate through a vacuum medium.

• The speed of sound differs in gasses, liquids, and solids. This is due to the differences in the strength of the interatomic forces and closeness of the atoms in the three states.

• Compressions and rarefactions propagate faster in denser media.

• Sound travels faster in liquids than in gasses and fastest in solids.

Medium Speed (m s∙ -1)Air 346

Hydrogen 1340Water 1500

Flint glasses 4540Iron (steel) 5200

Granite 5400

Comparison of the speed of sound in different

media at 25o C

EchoesEchoes happen if the reflected sound is heardafter an interval of silence.

Example :

A boy standing 68 m from a high wall claps his hands and hears an echo 0.4 s later. Find the speed of sound in air.

Total distance travelled by sound = 2 x 68 m

Time taken = 0.4 s

Speed of sound = distance travelled / time taken

= ( 2 x 68) / 0.4

= 340 m s -1

• Sound is heard when the compressions and rarefactions reach the ear and set the eardrum vibrating.

• The human ear can hear sounds of frequencies in the range of 20 Hz to 20 000 Hz. This frequency range is reffered to as the range of audible frequency.

Assignment :• Group work• Make a display about the

common sounds with an estimate of their intensity and decibel level, infrasonic, and ultrasonic

• Display must be completed in two weeks

- end of presentation -Thank you for watching