140
5 Acoustics in Biology and Medicine
the pulse was emitted. The greatest wave amplitude will occur on a cone, with axis
along the body’s motion, and vertex at the position of the body. The half vertex
angle of the cone will be θ c = arcsin (v/u). The figure shows wave fronts from
sound emanating from the moving source, adding coherently on the cone’s surface.
This is where the sound shock wave exists. 20
If the object were a supersonic airplane (or a meteor entering our atmosphere),
the lower part of the cone produces a ‘sonic boom’ across the ground.
5.14 Non-biological Sound Wave Production
5.14.1 Mechanically Generated Sounds
Vibratory mechanical motion in a medium produces sound. Sound-producing
mechanical devices transform a fraction of their kinetic energy into sound energy.
A jet engine produces sound by the whir of a turbine fan and the turbulent kinetic
motion of hot air exiting the engine, producing sound power of the order of a few
kilowatts.
Whistles and sirens operate by interrupting the flow of air, generating air
turbulence. The rapid changes in air pressure near the instrument radiates sound
waves. Sirens can produce extremely intense sound waves, sufficient to cause a
cotton shirt to catch fire. 21 Sirens have frequencies from 0.1 to 100 MHz, and sound
intensities up to 30 kW/cm 2 (205 dB).
The table below lists some of the highest power sounds produced in air. Their
sound levels have been calculated at 1 km from the source.
Event
Sound power in Watts
Sound level at r = 1 km
Tunguska 1908 comet explosion
1.26 × 10 27 W
320 dB ∗
Krakatoa 1883 eruption
5.00 × 10 16 W
216 dB ∗
USSR Tsar Bomba
1.26 × 10 13 W
180 dB
Saturn V launch
7.93 × 10 11 W
168 dB
1 ton TNT explosion
3.16 × 10 10 W
154 dB
Bell-Chrysler siren
5.00 × 10 6 W
116 dB
Thunder clap
1.00 × 10 6 W
109 dB
20 Electromagnetic shock waves can also be produced. Charges moving through ordinary material
faster than light moves in that material will radiate. This ‘Cherenkov’ radiation is observed as a
blue glow in the water used to shield an operating nuclear reactor.
21 This experiment is best done without a person wearing the shirt.
5 Acoustics in Biology and Medicine
the pulse was emitted. The greatest wave amplitude will occur on a cone, with axis
along the body’s motion, and vertex at the position of the body. The half vertex
angle of the cone will be θ c = arcsin (v/u). The figure shows wave fronts from
sound emanating from the moving source, adding coherently on the cone’s surface.
This is where the sound shock wave exists. 20
If the object were a supersonic airplane (or a meteor entering our atmosphere),
the lower part of the cone produces a ‘sonic boom’ across the ground.
5.14 Non-biological Sound Wave Production
5.14.1 Mechanically Generated Sounds
Vibratory mechanical motion in a medium produces sound. Sound-producing
mechanical devices transform a fraction of their kinetic energy into sound energy.
A jet engine produces sound by the whir of a turbine fan and the turbulent kinetic
motion of hot air exiting the engine, producing sound power of the order of a few
kilowatts.
Whistles and sirens operate by interrupting the flow of air, generating air
turbulence. The rapid changes in air pressure near the instrument radiates sound
waves. Sirens can produce extremely intense sound waves, sufficient to cause a
cotton shirt to catch fire. 21 Sirens have frequencies from 0.1 to 100 MHz, and sound
intensities up to 30 kW/cm 2 (205 dB).
The table below lists some of the highest power sounds produced in air. Their
sound levels have been calculated at 1 km from the source.
Event
Sound power in Watts
Sound level at r = 1 km
Tunguska 1908 comet explosion
1.26 × 10 27 W
320 dB ∗
Krakatoa 1883 eruption
5.00 × 10 16 W
216 dB ∗
USSR Tsar Bomba
1.26 × 10 13 W
180 dB
Saturn V launch
7.93 × 10 11 W
168 dB
1 ton TNT explosion
3.16 × 10 10 W
154 dB
Bell-Chrysler siren
5.00 × 10 6 W
116 dB
Thunder clap
1.00 × 10 6 W
109 dB
20 Electromagnetic shock waves can also be produced. Charges moving through ordinary material
faster than light moves in that material will radiate. This ‘Cherenkov’ radiation is observed as a
blue glow in the water used to shield an operating nuclear reactor.
21 This experiment is best done without a person wearing the shirt.