Oscillatory motion

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· Sound is an external effect affects on ear causing sense of hearing.

· Sound is produced due to vibration of bodies, and it stops when vibration stops.

· Sound is mechanical longitudinal waves, propagate in medium as spherical waves and its centre is the source of sound.

· Sound velocity in air is 340 m/sec and it increases or decreases in different media.

Properties of sound are:

1) Sound pitch

2) Sound intensity

3) Sound quality

1- Sound pitch:

Ø The property by which human ear can distinguish between sharp and rough sounds.

Ø Sound pitch depends on frequency:

- High frequency :- sharp

- Low frequency :- rough

2- Sound intensity:

Ø The property by which the human ear can distinguish between strong and weak sounds.

Sound intensity is measured by unit Watt/m2

Intensity of noise is measured by unit Decibel.

Ø Factors that affect sound intensity:

a- Distance between sound source and ear

b- Amplitude of sound

c- Surface area of vibration

d- Density of medium

e- Wind direction

Ø Application on sound intensity:

Ears blocks that are made of silicon to protect ears from noise.

3- Sound quality

Ø The property by which human ear can distinguish between sounds from different sources even they have the same pitch and intensity.

Ø We can distinguish between sounds due to presence of harmonic waves that accompany the fundamental waves produced.

Ø Audible and non-audible waves.

Ø Audible waves (sonic waves) have frequency ranges between 20:20.000 Hz.

Ø Non-audible waves:

- Infrasonic waves’ frequency less than 20 Hz.

- Ultrasonic waves’ frequency more than 20.000 Hz.

Uses of ultrasonic waves:

1) Decaying of stones in kidney and ureters.

2) Diagnosis of some diseases and treatment of cancer.

3) Sterilizing of food.

4) Detection of explosives underground (Landmines).
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