Acoustics
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Transcript of Acoustics
Sound Defined
All sounds are produced by the
vibrations of material objects.
It is a longitudinal wave that carries
energy produced by vibrations of matter
and is propagated through a
medium such as solid, liquid or gas.
Not all sounds are audible
Audible range for humans is between 20
Hz to 20000 Hz
Lower than this range is classified as
INFRASONIC
Higher than this range is classified as
ULTRASONIC
How about INFRASONICS?
Sources include earthquakes, thunder,
volcanoes and waves produced by
vibrating heavy machinery
May pose damage to human body including
irritation of internal organs
Density and Elasticity of the Medium (Solid)
The denser and more elastic the medium,
the faster the transmission of sound.
v – velocity of sound
Y – elastic modulus of
the solid medium
ρ – density of the solid
medium
Sample Problem 1
Find the speed of sound in an aluminum rod
at a temperature of 20°C. The Young’s
modulus for aluminum is 70 x 109 N/m2 and
its density is 2.7 x 103 kg/m3.
Density and Elasticity of the Medium (Liquid)
The denser and more elastic the medium,
the faster the transmission of sound.
v – velocity of sound
B – bulk modulus of the
solid medium
ρ – density of the liquid
medium
Sample Problem 2
Find the speed of sound in water at a
temperature of 20°C. The bulk modulus of
water is 2.2 x 109 N/m2 and its density is 1.0 x
103 kg/m3.
The Speed of Sound in Various Solid Media
Medium Speed (m/s)
Aluminum 5100
Copper 3500
Iron 4500
Glass 5200
Polystyren
e
1850
Sound Speed in Air and Temperature
As temperature increases, sound speed in
air increases at a definite rate.
Vsound = (Vsound at 0°C + 0.6T°C)m/s
Vsound at 0°C = 331 m/s
Sample Problem 3
In the cold months of December and
January, the temperature in Baguio can go
down to 10°C. What is the speed of sound in
air?
Sample Problem 4
An automatic focus camera is able to focus on objects by use of an ultrasonic sound wave. The camera sends out sound waves that reflect off distant objects and return to the camera. A sensor detects the time it takes for the waves to return and then determines the distance an object is from the camera. If the temperature of the air is 20°C and the infrasonic frequency returns to the camera 0.150 seconds after leaving the camera, how far away is the object?