16.6 The Speed of Sound • Sound travels through gases, liquids, and solids at different speeds. • Room temperature: speed of sound in air is 343 m/s (767 mi/h) and greater in liquids and solids. • Sound travels more than four times faster in water and more than seventeen times faster in steel than it does in air. • Sound travels slowest in gases,
16.6 The Speed of Sound. Sound travels through gases, liquids, and solids at different speeds. Room temperature: speed of sound in air is 343 m/s (767 mi/h) and greater in liquids and solids. - PowerPoint PPT Presentation
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16.6 The Speed of Sound• Sound travels through gases, liquids, and
solids at different speeds.• Room temperature: speed of sound in air
is 343 m/s (767 mi/h) and greater in liquids and solids.
• Sound travels more than four times faster in water and more than seventeen times faster in steel than it does in air.
• Sound travels slowest in gases, faster in liquids, and fastest in solids.
• In a liquid, the speed of sound depends on the density p and the adiabatic bulk modulus Bad of the liquid:
(16.6)
Liquids
• Adiabatic bulk modulus Bad (substance's resistance to uniform compression) is used when calculating the speed of sound in liquids.
• In seawater sound is 1522m/s (4x greater than in air).
In Medicine• Ultrasonic probe called an A-scan is used
to measure the length of the eyeball in front of the lens, thickness of the lens, and the length of the eyeball between the lens and the retina.
• Needed information is the speed of sound in the material in front of and behind the lens of the eye is 1532m/s and that within the lens is 1641m/s.
Solid Bars
• When sound travels through a long slender solid bar, the speed of the sound depends on the properties of the medium according to
16.7 Sound Intensity
• Sound waves carry energy that can be used to do work.
• Sonic boom: can carry enough energy to cause damage to windows and buildings.
• The amount of energy transported per second by a sound wave is called the power of the wave and is measure in SI units of joules per second (J/s) or watts (W).
• Power spreads out as it leaves the source.• It spreads out but has the same power
even when spread out over a greater area.• Sound Intensity I: sound power P that
passes perpendicularly through a surface divided by the area A of that surface:
Example 6: Sound Intensities
• The sound intensity is less at the more distant surface, where the same power passes through a threefold greater area. The ear of a listener, with its fixed area, intercepts less power where the intensity, or power per unit area, is smaller. Thus listener 2 intercepts less of the sound power than listener 1. With less power striking the ear, the sound is quieter.
Threshold of Hearing
• For a 1000Hz tone, the smallest sound intensity that the human ear can detect is about 1x10^-12W/m2. (threshold of hearing)
• Intensities greater than 1 W/m2 can be painful and result in permanent hearing damage if continuously exposed to them.
• A source emits sound uniformly in all directions, the intensity depends on distance.
• If the source is at the center of an imaginary sphere. The radius of the sphere is r. Since all the radiated sound power P passes through the spherical surface of A = , the intensity at a distance r is.