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Speed of sound
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For other uses, see Speed of sound (disambiguation).
Sound measurements
Characteristic
Symbols
Sound pressure
p, SPL,LPA
Particle velocity
v, SVL
Particle displacement
δ
Sound intensity
I, SIL
Sound power
P, SWL, LWA
Sound energy
W
Sound energy density
w
Sound exposure
E, SEL
Acoustic impedance
Z
Speed of sound
c
Audio frequency
AF
Transmission loss
TL
v
t
e
The speed of sound is the distance travelled per unit time by a sound wave as it propagates through an elastic medium. In dry air at 0 °C (32 °F), the speed of sound is 331.2 metres per second (1,087 ft/s; 1,192 km/h; 741 mph; 644 kn). At 20 °C (68 °F), the speed of sound is 343 metres per second (1,125 ft/s; 1,235 km/h; 767 mph; 667 kn), or a kilometre in 2.91 s or a mile in 4.69 s.
The speed of sound in an ideal gas depends only on its temperature and composition. The speed has a weak dependence on frequency and pressure in ordinary air, deviating slightly from ideal behavior.
In common everyday speech, speed of sound refers to the speed of sound waves in air. However, the speed of sound varies from substance to substance: sound travels most slowly in gases; it travels faster in liquids; and faster still in solids. For example, (as noted above), sound travels at 343 m/s in air; it travels at 1,484 m/s in water (4.3 times as fast as in air); and at 5,120 m/s in iron (about 15 times as fast as in air). In an exceptionally stiff material such as diamond, sound travels at 12,000 metres per second (26,843 mph);[1] (about 35 times as fast as in air) which is around the maximum speed that sound will travel under normal conditions.
Sound waves in solids are composed of compression waves (just as in gases and liquids), and a different type of sound wave called a shear wave, which occurs only in solids. Shear waves in solids usually travel at different speeds, as exhibited in seismology. The speed of compression waves in solids is determined by the medium's compressibility, shear modulus and density. The speed of shear waves is determined only by the solid material's shear modulus and density.
In fluid dynamics, the speed of sound in a fluid medium (gas or liquid) is used as a relative measure for the speed of an object moving through the medium. The ratio of the speed of an object to the speed of sound in the fluid is called the object's Mach number. Objects moving at speeds greater than Mach1 are said to be traveling at supersonic speeds.
Contents
[hide]
1 History
2 Basic concepts
2.1 Compression and shear waves
3 Equations
4 Dependence on the properties of the medium
5 Altitude variation and implications for atmospheric acoustics
6 Practical formula for dry air
7 Details
7.1 Speed of sound in ideal gases and air
7.2 Effects due to wind shear
7.3 Tables
8 Effect of frequency and gas composition
8.1 General physical considerations
8.2 Practical application to air
9 Mach number
10 Experimental methods
10.1 Single-shot timing methods
10.2 Other methods
10.3 High-precision measurements in air
11 Non-gaseous media
11.1 Speed of sound in solids
11.1.1 Three-dimensional solids
11.1.2 One-dimensional solids
11.2 Speed of sound in liquids
11.2.1 Water
11.2.2 Seawater
11.3 Speed of sound in plasma
12 Gradients
13 See also
14 References
15 External links
History[edit]
Sir Isaac Newton computed the speed of sound in air as 979 feet per second (298 m/s), which is too low by about 15%,[2]. Newton's analysis was good save for neglecting the (then unknown) effect of rapidly-fluctuating temperature in a sound wave (in modern terms, sound wave compression and expansion of air is an adiabatic process, not an isothermal process). This error was later rectified by Laplace.[3]
During the 17th century, there were several attempts to measure the speed of sound accurately, including attempts by Marin Mersenne in 1630 (1,380 Parisian feet per second), Pierre Gassendi in 1635 (1,473 Parisian feet per second) and Robert Boyle (1,125 Parisian feet per second).[4]
In 1709, the Reverend William Derham, Rector of Upminster, published a more accurate measure of the speed of sound, at 1,072 Parisian feet per second.[4] Derham used a telescope from the tower of the church of St Laurence, Upminster to observe the flash of a distant shotgun being fired, and then measured the time until he heard the gunshot with a half second pendulum. Measurements were made of gunshots from a number of local landmarks, including North Ockendon church. The distance was known by triangulation, and thus the speed that the sound had travelled was calculated.[5]
Basic concepts[edit]
The transmission of sound can be illustrated by using a model consisting of an array of spherical objects interconnected by springs.
In real material terms, the spheres represent the material's molecules and the springs represent the bonds between them. Sound passes through the system by compressing and expanding the springs, transmitting the acoustic energy to neighboring spheres. This helps transmit the energy in-turn to the neighboring sphere's springs (bonds), and so on.
The speed of sound through the model depends on the stiffness/rigidity of the springs, and the mass of the spheres. As long as the spacing of the spheres remains constant, stiffer springs/bonds transmit energy quicker, while larger spheres transmit the energy slower. Effects like dispersion and reflection can also be understood using this model.[citation needed]
In a real material, the stiffness of the springs is known as the "elastic modulus", and the mass corresponds to the material density. Given that all other things being equal (ceteris paribus), sound will travel slower in spongy materials, and faster in stiffer ones. For instance, sound will travel 1.59 times faster in nickel than in bronze, due to the greater stiffness of nickel at about the same density. Similarly, sound travels about 1.41 times faster in light hydrogen (protium) gas than in heavy hydrogen (deuterium) gas, since deuterium has similar properties but twice the density. At the same time, "compression-type" sound will travel faster in solids than in liquids, and faster in liquids than in gases, because the solids are more difficult to compress than liquids, while liquids in turn are more difficult to compress than gases.
Some textbooks mistakenly state that the speed of sound increases with increasing density. This is usually illustrated by presenting data for three materials, such as air, water and steel, which also have vastly different levels compressibilities which more than make up for the density differences. An illustrative example of the two effects is that sound travels only 4.3 times faster in water than air, despite enormous differences in compressibility of the two media. The reason is that the larger density of water, which works to slow sound in water relative to air, nearly makes up for the compressibility differences in the two media.
A practical example can be observed in Edinburgh, when the "One o' Clock Gun" is fired at the eastern end of Edinburgh Castle. Standing at the base of the western end of the Castle Rock, the sound of the Gun can be heard through the rock, slightly before it arrives by the air route, partly delayed by the slightly longer route. It is particularly effective if a multi-gun salute such as for "The Queen's Birthday" is being fired.
Compression and shear waves[edit]
Pressure-pulse or compression-type wave (longitudinal wave) confined to a plane. This is the only type of sound wave that travels in fluids (gases and liquids). A pressure-type wave may also travel in solids, along with other types of waves (transverse waves, see below)
Transverse wave affecting atoms initially confined to a plane. This additional type of sound wave (additional type of elastic wave) travels only in solids, for it requires a sideways shearing motion which is supported by the presence of elasticity in the solid. The sideways shearing motion may take place in any direction which is at right-angle to the direction of wave-travel (only one shear direction is shown here, at right angles to the plane). Furthermore, the right-angle shear direction may change over time and distance, resulting in different types of polarization of shear-waves
In a gas or liquid, sound consists of compression waves. In solids, waves propagate as two different types. A longitudinal wave is associated with compression and decompression in the direction of travel, and is the same process in gases and liquids, with an analogous compression-type wave in solids. Only compression waves are supported in gases and liquids. An additional type of wave, the transverse wave, also called a shear wave, occurs only in solids because only solids support elastic deformations. It is due to elastic deformation of the medium perpendicular to the direction of wave travel; the direction of shear-deformation is called the "polarization" of this type of wave. In general, transverse waves occur as a pair of orthogonal polarizations.
These different waves (compression waves and the different polarizations of shear waves) may have different speeds at the same frequency. Therefore, they arrive at an observer at different times, an extreme example being an earthquake, where sharp compression waves arrive first, and rocking transverse waves seconds later.
The speed of a compression wave in fluid is determined by the medium's compressibility and density. In solids, the compression waves are analogous to those in fluids, depending on compressibility and density, but with the additional factor of shear modulus which affects compression waves due to off-axis elastic energies which are able to influence effective tension and relaxation in a compression. The speed of shear waves, which can occur only in solids, is determined simply by the solid material's shear modulus and density.
Equations[edit]
The speed of sound in mathematical notation is conventionally represented by c, from the Latin celeritas meaning "velocity".
For fluids in general, the speed of sound c is given by the Newton–Laplace equation:
c = K s ρ , {\displaystyle c={\sqrt {\frac {K_{s}}{\rho }}},}
where
Ks is a coefficient of stiffness, the isentropic bulk modulus (or the modulus of bulk elasticity for gases);
ρ is the density.
Thus the speed of sound increases with the stiffness (the resistance of an elastic body to deformation by an applied force) of the material, and decreases with increase in density. For ideal gases the bulk modulus K is simply the gas pressure multiplied by the dimensionless adiabatic index, which is about 1.4 for air under normal conditions of pressure and temperature.
For general equations of state, if classical mechanics is used, the speed of sound c is given by
c = ( ∂ p ∂ ρ ) s , {\displaystyle c={\sqrt {\left({\frac {\partial p}{\partial \rho }}\right)_{s}}},}
where
p is the pressure;
ρ is the density and the derivative is taken isentropically, that is, at constant entropy s.
If relativistic effects are important, the speed of sound is calculated from the relativistic Euler equations.
In a non-dispersive medium, the speed of sound is independent of sound frequency, so the speeds of energy transport and sound propagation are the same for all frequencies. Air, a mixture of oxygen and nitrogen, constitutes a non-dispersive medium. However, air does contain a small amount of CO2 which is a dispersive medium, and causes dispersion to air at ultrasonic frequencies (> 28 kHz).[6]
In a dispersive medium, the speed of sound is a function of sound frequency, through the dispersion relation. Each frequency component propagates at its own speed, called the phase velocity, while the energy of the disturbance propagates at the group velocity. The same phenomenon occurs with light waves; see optical dispersion for a description.
Dependence on the properties of the medium[edit]
The speed of sound is variable and depends on the properties of the substance through which the wave is travelling. In solids, the speed of transverse (or shear) waves depends on the shear deformation under shear stress (called the shear modulus), and the density of the medium. Longitudinal (or compression) waves in solids depend on the same two factors with the addition of a dependence on compressibility.
In fluids, only the medium's compressibility and density are the important factors, since fluids do not transmit shear stresses. In heterogeneous fluids, such as a liquid filled with gas bubbles, the density of the liquid and the compressibility of the gas affect the speed of sound in an additive manner, as demonstrated in the hot chocolate effect.
In gases, adiabatic compressibility is directly related to pressure through the heat capacity ratio (adiabatic index), while pressure and density are inversely related to the temperature and molecular weight, thus making only the completely independent properties of temperature and molecular structure important (heat capacity ratio may be determined by temperature and molecular structure, but simple molecular weight is not sufficient to determine it).
In low molecular weight gases such as helium, sound propagates faster as compared to heavier gases such as xenon. For monatomic gases, the speed of sound is about 75% of the mean speed that the atoms move in that gas.
For a given ideal gas the molecular composition is fixed, and thus the speed of sound depends only on its temperature. At a constant temperature, the gas pressure has no effect on the speed of sound, since the density will increase, and since pressure and density (also proportional to pressure) have equal but opposite effects on the speed of sound, and the two contributions cancel out exactly. In a similar way, compression waves in solids depend both on compressibility and density—just as in liquids—but in gases the density contributes to the compressibility in such a way that some part of each attribute factors out, leaving only a dependence on temperature, molecular weight, and heat capacity ratio which can be independently derived from temperature and molecular composition (see derivations below). Thus, for a single given gas (assuming the molecular weight does not change) and over a small temperature range (for which the heat capacity is relatively constant), the speed of sound becomes dependent on only the temperature of the gas.
In non-ideal gas behavior regimen, for which the van der Waals gas equation would be used, the proportionality is not exact, and there is a slight dependence of sound velocity on the gas pressure.
Humidity has a small but measurable effect on the speed of sound (causing it to increase by about 0.1%–0.6%), because oxygen and nitrogen molecules of the air are replaced by lighter molecules of water. This is a simple mixing effect.
Altitude variation and implications for atmospheric acoustics[edit]
Density and pressure decrease smoothly with altitude, but temperature (red) does not. The speed of sound (blue) depends only on the complicated temperature variation at altitude and can be calculated from it, since isolated density and pressure effects on the speed of sound cancel each other. Speed of sound increases with height in two regions of the stratosphere and thermosphere, due to heating effects in these regions.
In the Earth's atmosphere, the chief factor affecting the speed of sound is the temperature. For a given ideal gas with constant heat capacity and composition, the speed of sound is dependent solely upon temperature; see Details below. In such an ideal case, the effects of decreased density and decreased pressure of altitude cancel each other out, save for the residual effect of temperature.
Since temperature (and thus the speed of sound) decreases with increasing altitude up to 11 km, sound is refracted upward, away from listeners on the ground, creating an acoustic shadow at some distance from the source.[7] The decrease of the speed of sound with height is referred to as a negative sound speed gradient.
However, there are variations in this trend above 11 km. In particular, in the stratosphere above about 20 km, the speed of sound increases with height, due to an increase in temperature from heating within the ozone layer. This produces a positive speed of sound gradient in this region. Still another region of positive gradient occurs at very high altitudes, in the aptly-named thermosphere above 90 km.
Practical formula for dry air[edit]
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Approximation of the speed of sound in dry air based on the heat capacity ratio (in green) against the truncated Taylor expansion (in red).
The approximate speed of sound in dry (0% humidity) air, in meters per second, at temperatures near 0 °C, can be calculated from
c a i r = ( 331.3 + 0.606 ⋅ ϑ ) m / s , {\displaystyle c_{\mathrm {air} }=(331.3+0.606\cdot \vartheta )~~~\mathrm {m/s} ,}
where ϑ {\displaystyle \vartheta } is the temperature in degrees Celsius (°C).
This equation is derived from the first two terms of the Taylor expansion of the following more accurate equation:
c a i r = 331.3 1 + ϑ 273.15 m / s . {\displaystyle c_{\mathrm {air} }=331.3~{\sqrt {1+{\frac {\vartheta }{273.15}}}}~~~~\mathrm {m/s} .}
Dividing the first part, and multiplying the second part, on the right hand side, by √273.15 gives the exactly equivalent form
c a i r = 20.05 ϑ + 273.15 m / s . {\displaystyle c_{\mathrm {air} }=20.05~{\sqrt {\vartheta +273.15}}~~~~\mathrm {m/s} .}
which can also be written as
c a i r = 20.05 T / K m / s {\displaystyle c_{\mathrm {air} }=20.05~{\sqrt {T/K}}~~~~\mathrm {m/s} }
where T denotes the thermodynamic temperature.
The value of 331.3 m/s, which represents the speed at 0 °C (or 273.15 K), is based on theoretical (and some measured) values of the heat capacity ratio, γ, as well as on the fact that at 1 atm real air is very well described by the ideal gas approximation. Commonly found values for the speed of sound at 0 °C may vary from 331.2 to 331.6 due to the assumptions made when it is calculated. If ideal gas γ is assumed to be 7/5 = 1.4 exactly, the 0 °C speed is calculated (see section below) to be 331.3 m/s, the coefficient used above.
This equation is correct to a much wider temperature range, but still depends on the approximation of heat capacity ratio being independent of temperature, and for this reason will fail, particularly at higher temperatures. It gives good predictions in relatively dry, cold, low pressure conditions, such as the Earth's stratosphere. The equation fails at extremely low pressures and short wavelengths, due to dependence on the assumption that the wavelength of the sound in the gas is much longer than the average mean free path between gas molecule collisions. A derivation of these equations will be given in the following section.
A graph comparing results of the two equations is at right, using the slightly different value of 331.5 m/s for the speed of sound at 0 °C.
Details[edit]
Speed of sound in ideal gases and air[edit]
For an ideal gas, K (the bulk modulus in equations above, equivalent to C, the coefficient of stiffness in solids) is given by
K = γ ⋅ p , {\displaystyle K=\gamma \cdot p,}
thus, from the Newton–Laplace equation above, the speed of sound in an ideal gas is given by
c = γ ⋅ p ρ , {\displaystyle c={\sqrt {\gamma \cdot {p \over \rho }}},}
where
γ is the adiabatic index also known as the isentropic expansion factor. It is the ratio of specific heats of a gas at a constant-pressure to a gas at a constant-volume( C p / C v {\displaystyle C_{p}/C_{v}} ), and arises because a classical sound wave induces an adiabatic compression, in which the heat of the compression does not have enough time to escape the pressure pulse, and thus contributes to the pressure induced by the compression;
p is the pressure;
ρ is the density.
Using the ideal gas law to replace p with nRT/V, and replacing ρ with nM/V, the equation for an ideal gas becomes
c i d e a l = γ ⋅ p ρ = γ ⋅ R ⋅ T M = γ ⋅ k ⋅ T m , {\displaystyle c_{\mathrm {ideal} }={\sqrt {\gamma \cdot {p \over \rho }}}={\sqrt {\gamma \cdot R\cdot T \over M}}={\sqrt {\gamma \cdot k\cdot T \over m}},}
where
cideal is the speed of sound in an ideal gas;
R (approximately 8.314,5 J · mol−1 · K−1) is the molar gas constant(universal gas constant);[8]
k is the Boltzmann constant;
γ (gamma) is the adiabatic index. At room temperature, where thermal energy is fully partitioned into rotation (rotations are fully excited) but quantum effects prevent excitation of vibrational modes, the value is 7/5 = 1.400 for diatomic molecules, according to kinetic theory. Gamma is actually experimentally measured over a range from 1.399,1 to 1.403 at 0 °C, for air. Gamma is exactly 5/3 = 1.6667 for monatomic gases such as noble gases;
T is the absolute temperature;
M is the molar mass of the gas. The mean molar mass for dry air is about 0.028,964,5 kg/mol;[citation needed]
n is the number of moles;
m is the mass of a single molecule.
This equation applies only when the sound wave is a small perturbation on the ambient condition, and the certain other noted conditions are fulfilled, as noted below. Calculated values for cair have been found to vary slightly from experimentally determined values.[9]
Newton famously considered the speed of sound before most of the development of thermodynamics and so incorrectly used isothermal calculations instead of adiabatic. His result was missing the factor of γ but was otherwise correct.
Numerical substitution of the above values gives the ideal gas approximation of sound velocity for gases, which is accurate at relatively low gas pressures and densities (for air, this includes standard Earth sea-level conditions). Also, for diatomic gases the use of γ = 1.4000 requires that the gas exists in a temperature range high enough that rotational heat capacity is fully excited (i.e., molecular rotation is fully used as a heat energy "partition" or reservoir); but at the same time the temperature must be low enough that molecular vibrational modes contribute no heat capacity (i.e., insignificant heat goes into vibration, as all vibrational quantum modes above the minimum-energy-mode, have energies too high to be populated by a significant number of molecules at this temperature). For air, these conditions are fulfilled at room temperature, and also temperatures considerably below room temperature (see tables below). See the section on gases in specific heat capacity for a more complete discussion of this phenomenon.
For air, we introduce the shorthand
R ∗ = R / M a i r . {\displaystyle R_{*}=R/M_{\mathrm {air} }.}
In addition, we switch to the Celsius temperature ϑ {\displaystyle \vartheta } = T − 273.15, which is useful to calculate air speed in the region near 0°C (about 273 kelvin). Then, for dry air,
c i d e a l = γ ⋅ R ∗ ⋅ T = γ ⋅ R ∗ ⋅ ( ϑ + 273.15 ) , {\displaystyle c_{\mathrm {ideal} }={\sqrt {\gamma \cdot R_{*}\cdot T}}={\sqrt {\gamma \cdot R_{*}\cdot (\vartheta +273.15)}},}
c i d e a l = γ ⋅ R ∗ ⋅ 273.15 ⋅ 1 + ϑ 273.15 , {\displaystyle c_{\mathrm {ideal} }={\sqrt {\gamma \cdot R_{*}\cdot 273.15}}\cdot {\sqrt {1+{\frac {\vartheta }{273.15}}}},}
where ϑ {\displaystyle \vartheta } (theta) is the temperature in degrees Celsius(°C).
Substituting numerical values
R = 8.314 510 J / ( m o l ⋅ K ) {\displaystyle R=8.314\,510~\mathrm {J/(mol\cdot K)} }
for the molar gas constant in J/mole/Kelvin, and
M a i r = 0.028 964 5 k g / m o l {\displaystyle M_{\mathrm {air} }=0.028\,964\,5~\mathrm {kg/mol} }
for the mean molar mass of air, in kg; and using the ideal diatomic gas value of γ = 1.4000, we have
c a i r = 331.3 1 + ϑ 273.15 m / s . {\displaystyle c_{\mathrm {air} }=331.3~~{\sqrt {1+{\frac {\vartheta }{273.15}}}}~~~\mathrm {m/s} .}
Finally, Taylor expansion of the remaining square root in ϑ {\displaystyle \vartheta } yields
c a i r = 331.3 ( 1 + ϑ 2 ⋅ 273.15 ) m / s , {\displaystyle c_{\mathrm {air} }=331.3~(1+{\frac {\vartheta }{2\cdot 273.15}})~~~\mathrm {m/s} ,}
c a i r = ( 331.3 + 0.606 ⋅ ϑ ) m / s . {\displaystyle c_{\mathrm {air} }=(331.3+0.606\cdot \vartheta )~~~\mathrm {m/s} .}
The above derivation includes the first two equations given in the "Practical formula for dry air" section above.
Effects due to wind shear[edit]
The speed of sound varies with temperature. Since temperature and sound velocity normally decrease with increasing altitude, sound is refracted upward, away from listeners on the ground, creating an acoustic shadow at some distance from the source.[7] Wind shear of 4 m/(s · km) can produce refraction equal to a typical temperature lapse rate of 7.5 °C/km.[10] Higher values of wind gradient will refract sound downward toward the surface in the downwind direction,[11] eliminating the acoustic shadow on the downwind side. This will increase the audibility of sounds downwind. This downwind refraction effect occurs because there is a wind gradient; the sound is not being carried along by the wind.[12]
For sound propagation, the exponential variation of wind speed with height can be defined as follows:[13]
U ( h ) = U ( 0 ) h ζ , {\displaystyle U(h)=U(0)h^{\zeta },}
d U d H ( h ) = ζ U ( h ) h , {\displaystyle {\frac {\mathrm {d} U}{\mathrm {d} H}}(h)=\zeta {\frac {U(h)}{h}},}
where
U(h) is the speed of the wind at height h;
ζ is the exponential coefficient based on ground surface roughness, typically between 0.08 and 0.52;
dU/dH(h) is the expected wind gradient at height h.
In the 1862 American Civil War Battle of Iuka, an acoustic shadow, believed to have been enhanced by a northeast wind, kept two divisions of Union soldiers out of the battle,[14] because they could not hear the sounds of battle only 10 km (six miles) downwind.[15]
Tables[edit]
In the standard atmosphere:
T0 is 273.15 K (= 0 °C = 32 °F), giving a theoretical value of 331.3 m/s (= 1086.9 ft/s = 1193 km/h = 741.1 mph = 644.0 kn). Values ranging from 331.3 to 331.6 m/s may be found in reference literature, however;
T20 is 293.15 K (= 20 °C = 68 °F), giving a value of 343.2 m/s (= 1126.0 ft/s = 1236 km/h = 767.8 mph = 667.2 kn);
T25 is 298.15 K (= 25 °C = 77 °F), giving a value of 346.1 m/s (= 1135.6 ft/s = 1246 km/h = 774.3 mph = 672.8 kn).
In fact, assuming an ideal gas, the speed of sound c depends on temperature only, not on the pressure or density (since these change in lockstep for a given temperature and cancel out). Air is almost an ideal gas. The temperature of the air varies with altitude, giving the following variations in the speed of sound using the standard atmosphere—actual conditions may vary.
Effect of temperature on properties of air
Temperature
T (°C)
Speed of sound
c (m/s)
Density of air
ρ (kg/m3)
Characteristic specific acoustic impedance
z0 (Pa·s/m)
35 351.88 1.1455 403.2
30 349.02 1.1644 406.5
25 346.13 1.1839 409.4
20 343.21 1.2041 413.3
15 340.27 1.2250 416.9
10 337.31 1.2466 420.5
5 334.32 1.2690 424.3
0 331.30 1.2922 428.0
−5 328.25 1.3163 432.1
−10 325.18 1.3413 436.1
−15 322.07 1.3673 440.3
−20 318.94 1.3943 444.6
−25 315.77 1.4224 449.1
Given normal atmospheric conditions, the temperature, and thus speed of sound, varies with altitude:
Altitude Temperature m/s km/h mph kn
Sea level 15 °C (59 °F) 340 1,225 761 661
11,000 m−20,000 m
(Cruising altitude of commercial jets,
and first supersonic flight) −57 °C (−70 °F) 295 1,062 660 573
29,000 m (Flight of X-43A) −48 °C (−53 °F) 301 1,083 673 585
Effect of frequency and gas composition[edit]
General physical considerations[edit]
The medium in which a sound wave is travelling does not always respond adiabatically, and as a result the speed of sound can vary with frequency.[16]
The limitations of the concept of speed of sound due to extreme attenuation are also of concern. The attenuation which exists at sea level for high frequencies applies to successively lower frequencies as atmospheric pressure decreases, or as the mean free path increases. For this reason, the concept of speed of sound (except for frequencies approaching zero) progressively loses its range of applicability at high altitudes.[9] The standard equations for the speed of sound apply with reasonable accuracy only to situations in which the wavelength of the soundwave is considerably longer than the mean free path of molecules in a gas.
The molecular composition of the gas contributes both as the mass (M) of the molecules, and their heat capacities, and so both have an influence on speed of sound. In general, at the same molecular mass, monatomic gases have slightly higher speed of sound (over 9% higher) because they have a higher γ (5/3 = 1.66…) than diatomics do (7/5 = 1.4). Thus, at the same molecular mass, the speed of sound of a monatomic gas goes up by a factor of
c g a s , m o n a t o m i c c g a s , d i a t o m i c = 5 / 3 7 / 5 = 25 21 = 1.091 … {\displaystyle {c_{\mathrm {gas,monatomic} } \over c_{\mathrm {gas,diatomic} }}={\sqrt {{5/3} \over {7/5}}}={\sqrt {25 \over 21}}=1.091\ldots }
This gives the 9% difference, and would be a typical ratio for speeds of sound at room temperature in helium vs. deuterium, each with a molecular weight of 4. Sound travels faster in helium than deuterium because adiabatic compression heats helium more, since the helium molecules can store heat energy from compression only in translation, but not rotation. Thus helium molecules (monatomic molecules) travel faster in a sound wave and transmit sound faster. (Sound travels at about 70% of the mean molecular speed in gases; the figure is 75% in monatomic gases and 68% in diatomic gases).
Note that in this example we have assumed that temperature is low enough that heat capacities are not influenced by molecular vibration (see heat capacity). However, vibrational modes simply cause gammas which decrease toward 1, since vibration modes in a polyatomic gas gives the gas additional ways to store heat which do not affect temperature, and thus do not affect molecular velocity and sound velocity. Thus, the effect of higher temperatures and vibrational heat capacity acts to increase the difference between the speed of sound in monatomic vs. polyatomic molecules, with the speed remaining greater in monatomics.
Practical application to air[edit]
By far the most important factor influencing the speed of sound in air is temperature. The speed is proportional to the square root of the absolute temperature, giving an increase of about 0.6 m/s per degree Celsius. For this reason, the pitch of a musical wind instrument increases as its temperature increases.
The speed of sound is raised by humidity but decreased by carbon dioxide. The difference between 0% and 100% humidity is about 1.5 m/s at standard pressure and temperature, but the size of the humidity effect increases dramatically with temperature. The carbon dioxide content of air is not fixed, due to both carbon pollution and human breath (e.g., in the air blown through wind instruments).
The dependence on frequency and pressure are normally insignificant in practical applications. In dry air, the speed of sound increases by about 0.1 m/s as the frequency rises from 10 Hz to 100 Hz. For audible frequencies above 100 Hz it is relatively constant. Standard values of the speed of sound are quoted in the limit of low frequencies, where the wavelength is large compared to the mean free path.[17]
Mach number[edit]
Main article: Mach number
U.S. Navy F/A-18 traveling near the speed of sound. The white halo consists of condensed water droplets formed by the sudden drop in air pressure behind the shock cone around the aircraft (see Prandtl-Glauert singularity).[18]
Mach number, a useful quantity in aerodynamics, is the ratio of air speed to the local speed of sound. At altitude, for reasons explained, Mach number is a function of temperature. Aircraft flight instruments, however, operate using pressure differential to compute Mach number, not temperature. The assumption is that a particular pressure represents a particular altitude and, therefore, a standard temperature. Aircraft flight instruments need to operate this way because the stagnation pressure sensed by a Pitot tube is dependent on altitude as well as speed.
Experimental methods[edit]
A range of different methods exist for the measurement of sound in air.
The earliest reasonably accurate estimate of the speed of sound in air was made by William Derham, and acknowledged by Isaac Newton. Derham had a telescope at the top of the tower of the Church of St Laurence in Upminster, England. On a calm day, a synchronized pocket watch would be given to an assistant who would fire a shotgun at a pre-determined time from a conspicuous point some miles away, across the countryside. This could be confirmed by telescope. He then measured the interval between seeing gunsmoke and arrival of the sound using a half-second pendulum. The distance from where the gun was fired was found by triangulation, and simple division (distance/time) provided velocity. Lastly, by making many observations, using a range of different distances, the inaccuracy of the half-second pendulum could be averaged out, giving his final estimate of the speed of sound. Modern stopwatches enable this method to be used today over distances as short as 200–400 meters, and not needing something as loud as a shotgun.
Single-shot timing methods[edit]
The simplest concept is the measurement made using two microphones and a fast recording device such as a digital storage scope. This method uses the following idea.
If a sound source and two microphones are arranged in a straight line, with the sound source at one end, then the following can be measured:
The distance between the microphones (x), called microphone basis.
The time of arrival between the signals (delay) reaching the different microphones (t).
Then v = x/t.
Other methods[edit]
In these methods the time measurement has been replaced by a measurement of the inverse of time (frequency).
Kundt's tube is an example of an experiment which can be used to measure the speed of sound in a small volume. It has the advantage of being able to measure the speed of sound in any gas. This method uses a powder to make the nodes and antinodes visible to the human eye. This is an example of a compact experimental setup.
A tuning fork can be held near the mouth of a long pipe which is dipping into a barrel of water. In this system it is the case that the pipe can be brought to resonance if the length of the air column in the pipe is equal to (1 + 2n)λ/4 where n is an integer. As the antinodal point for the pipe at the open end is slightly outside the mouth of the pipe it is best to find two or more points of resonance and then measure half a wavelength between these.
Here it is the case that v = fλ.
High-precision measurements in air[edit]
The effect from impurities can be significant when making high-precision measurements. Chemical desiccants can be used to dry the air, but will in turn contaminate the sample. The air can be dried cryogenically, but this has the effect of removing the carbon dioxide as well; therefore many high-precision measurements are performed with air free of carbon dioxide rather than with natural air. A 2002 review[19] found that a 1963 measurement by Smith and Harlow using a cylindrical resonator gave "the most probable value of the standard speed of sound to date." The experiment was done with air from which the carbon dioxide had been removed, but the result was then corrected for this effect so as to be applicable to real air. The experiments were done at 30 °C but corrected for temperature in order to report them at 0 °C. The result was 331.45 ± 0.01 m/s for dry air at STP, for frequencies from 93 Hz to 1,500 Hz.
Non-gaseous media[edit]
Speed of sound in solids[edit]
Three-dimensional solids[edit]
In a solid, there is a non-zero stiffness both for volumetric deformations and shear deformations. Hence, it is possible to generate sound waves with different velocities dependent on the deformation mode. Sound waves generating volumetric deformations (compression) and shear deformations (shearing) are called pressure waves (longitudinal waves) and shear waves (transverse waves), respectively. In earthquakes, the corresponding seismic waves are called P-waves (primary waves) and S-waves (secondary waves), respectively. The sound velocities of these two types of waves propagating in a homogeneous 3-dimensional solid are respectively given by[20]
c s o l i d , p = K + 4 3 G ρ = E ( 1 − ν ) ρ ( 1 + ν ) ( 1 − 2 ν ) , {\displaystyle c_{\mathrm {solid,p} }={\sqrt {\frac {K+{\frac {4}{3}}G}{\rho }}}={\sqrt {\frac {E(1-\nu )}{\rho (1+\nu )(1-2\nu )}}},}
c s o l i d , s = G ρ , {\displaystyle c_{\mathrm {solid,s} }={\sqrt {\frac {G}{\rho }}},}
where
K is the bulk modulus of the elastic materials;
G is the shear modulus of the elastic materials;
E is the Young's modulus;
ρ is the density;
ν is Poisson's ratio.
The last quantity is not an independent one, as E = 3K(1 − 2ν). Note that the speed of pressure waves depends both on the pressure and shear resistance properties of the material, while the speed of shear waves depends on the shear properties only.
Typically, pressure waves travel faster in materials than do shear waves, and in earthquakes this is the reason that the onset of an earthquake is often preceded by a quick upward-downward shock, before arrival of waves that produce a side-to-side motion. For example, for a typical steel alloy, K = 170 GPa, G = 80 GPa and ρ = 7,700 kg/m3, yielding a compressional speed csolid,p of 6,000 m/s.[20] This is in reasonable agreement with csolid,p measured experimentally at 5,930 m/s for a (possibly different) type of steel.[21] The shear speed csolid,s is estimated at 3,200 m/s using the same numbers.
One-dimensional solids[edit]
The speed of sound for pressure waves in stiff materials such as metals is sometimes given for "long rods" of the material in question, in which the speed is easier to measure. In rods where their diameter is shorter than a wavelength, the speed of pure pressure waves may be simplified and is given by:
c s o l i d = E ρ , {\displaystyle c_{\mathrm {solid} }={\sqrt {\frac {E}{\rho }}},}
where E is Young's modulus. This is similar to the expression for shear waves, save that Young's modulus replaces the shear modulus. This speed of sound for pressure waves in long rods will always be slightly less than the same speed in homogeneous 3-dimensional solids, and the ratio of the speeds in the two different types of objects depends on Poisson's ratio for the material.
Speed of sound in liquids[edit]
Speed of sound in water vs temperature.
In a fluid the only non-zero stiffness is to volumetric deformation (a fluid does not sustain shear forces).
Hence the speed of sound in a fluid is given by
c f l u i d = K ρ , {\displaystyle c_{\mathrm {fluid} }={\sqrt {\frac {K}{\rho }}},}
where K is the bulk modulus of the fluid.
Water[edit]
In fresh water, sound travels at about 1481 m/s at 20 °C (see the External Links section below for online calculators).[22] Applications of underwater sound can be found in sonar, acoustic communication and acoustical oceanography.
Seawater[edit]
See also: Sound speed profile
Speed of sound as a function of depth at a position north of Hawaii in the Pacific Ocean derived from the 2005 World Ocean Atlas. The SOFAR channel is centred on the minimum in the speed of sound at ca. 750-m depth.
In salt water that is free of air bubbles or suspended sediment, sound travels at about 1500 m/s (1500.235 m/s at 1000 kilopascals, 10 °C and 3% salinity by one method).[23] The speed of sound in seawater depends on pressure (hence depth), temperature (a change of 1 °C ~ 4 m/s), and salinity (a change of 1‰ ~ 1 m/s), and empirical equations have been derived to accurately calculate the speed of sound from these variables.[24][25] Other factors affecting the speed of sound are minor. Since temperature decreases with depth while pressure and generally salinity increase, the profile of the speed of sound with depth generally shows a characteristic curve which decreases to a minimum at a depth of several hundred meters, then increases again with increasing depth (right).[26] For more information see Dushaw et al.[27]
A simple empirical equation for the speed of sound in sea water with reasonable accuracy for the world's oceans is due to Mackenzie:[28]
c ( T , S , z ) = a 1 + a 2 T + a 3 T 2 + a 4 T 3 + a 5 ( S − 35 ) + a 6 z + a 7 z 2 + a 8 T ( S − 35 ) + a 9 T z 3 , {\displaystyle c(T,S,z)=a_{1}+a_{2}T+a_{3}T^{2}+a_{4}T^{3}+a_{5}(S-35)+a_{6}z+a_{7}z^{2}+a_{8}T(S-35)+a_{9}Tz^{3},}
where
T is the temperature in degrees Celsius;
S is the salinity in parts per thousand;
z is the depth in meters.
The constants a1, a2, …, a9 are
a 1 = 1 , 448.96 , a 2 = 4.591 , a 3 = − 5.304 × 10 − 2 , a 4 = 2.374 × 10 − 4 , a 5 = 1.340 , a 6 = 1.630 × 10 − 2 , a 7 = 1.675 × 10 − 7 , a 8 = − 1.025 × 10 − 2 , a 9 = − 7.139 × 10 − 13 , {\displaystyle {\begin{aligned}a_{1}&=1,448.96,&a_{2}&=4.591,&a_{3}&=-5.304\times 10^{-2},\\a_{4}&=2.374\times 10^{-4},&a_{5}&=1.340,&a_{6}&=1.630\times 10^{-2},\\a_{7}&=1.675\times 10^{-7},&a_{8}&=-1.025\times 10^{-2},&a_{9}&=-7.139\times 10^{-13},\end{aligned}}}
with check value 1550.744 m/s for T = 25 °C, S = 35 parts per thousand, z = 1,000 m. This equation has a standard error of 0.070 m/s for salinity between 25 and 40 ppt. See Technical Guides. Speed of Sound in Sea-Water for an online calculator.
Other equations for the speed of sound in sea water are accurate over a wide range of conditions, but are far more complicated, e.g., that by V. A. Del Grosso[29] and the Chen-Millero-Li Equation.[27][30]
Speed of sound in plasma[edit]
The speed of sound in a plasma for the common case that the electrons are hotter than the ions (but not too much hotter) is given by the formula (see here)
c s = ( γ Z k T e / m i ) 1 / 2 = 9.79 × 10 3 ( γ Z T e / μ ) 1 / 2 m / s , {\displaystyle c_{s}=(\gamma ZkT_{\mathrm {e} }/m_{\mathrm {i} })^{1/2}=9.79\times 10^{3}(\gamma ZT_{e}/\mu )^{1/2}~\mathrm {m/s} ,}
where
mi is the ion mass;
μ is the ratio of ion mass to proton mass μ = mi/mp;
Te is the electron temperature;
Z is the charge state;
k is Boltzmann constant;
γ is the adiabatic index.
In contrast to a gas, the pressure and the density are provided by separate species, the pressure by the electrons and the density by the ions. The two are coupled through a fluctuating electric field.
Gradients[edit]
Main article: Sound speed gradient
When sound spreads out evenly in all directions in three dimensions, the intensity drops in proportion to the inverse square of the distance. However, in the ocean there is a layer called the 'deep sound channel' or SOFAR channel which can confine sound waves at a particular depth.
In the SOFAR channel, the speed of sound is lower than that in the layers above and below. Just as light waves will refract towards a region of higher index, sound waves will refract towards a region where their speed is reduced. The result is that sound gets confined in the layer, much the way light can be confined in a sheet of glass or optical fiber. Thus, the sound is confined in essentially two dimensions. In two dimensions the intensity drops in proportion to only the inverse of the distance. This allows waves to travel much further before being undetectably faint.
A similar effect occurs in the atmosphere. Project Mogul successfully used this effect to detect a nuclear explosion at a considerable distance.
See also[edit]
Acoustoelastic effect
Elastic wave
Second sound
Sonic boom
Sound barrier
Underwater acoustics
Vibrations
References[edit]
Jump up ^ Speed of Sound
Jump up ^ "The Speed of Sound". mathpages.com. Retrieved 3 May 2015.
Jump up ^ Bannon, Mike; Kaputa, Frank. "The Newton–Laplace Equation and Speed of Sound". Thermal Jackets. Retrieved 3 May 2015.
^ Jump up to: a b Murdin, Paul (25 December 2008). Full Meridian of Glory: Perilous Adventures in the Competition to Measure the Earth. Springer Science & Business Media. pp. 35–36. ISBN 9780387755342.
Jump up ^ Fox, Tony (2003). Essex Journal. Essex Arch & Hist Soc. pp. 12–16.
Jump up ^ Dean, E. A. (August 1979). Atmospheric Effects on the Speed of Sound, Technical report of Defense Technical Information Center
^ Jump up to: a b Everest, F. (2001). The Master Handbook of Acoustics. New York: McGraw-Hill. pp. 262–263. ISBN 0-07-136097-2.
Jump up ^ "CODATA Value: molar gas constant". Physics.nist.gov. Retrieved 24 October 2010.
^ Jump up to: a b U.S. Standard Atmosphere, 1976, U.S. Government Printing Office, Washington, D.C., 1976.
Jump up ^ Uman, Martin (1984). Lightning. New York: Dover Publications. ISBN 0-486-64575-4.
Jump up ^ Volland, Hans (1995). Handbook of Atmospheric Electrodynamics. Boca Raton: CRC Press. p. 22. ISBN 0-8493-8647-0.
Jump up ^ Singal, S. (2005). Noise Pollution and Control Strategy. Oxford: Alpha Science International. p. 7. ISBN 1-84265-237-0. It may be seen that refraction effects occur only because there is a wind gradient and it is not due to the result of sound being convected along by the wind.
Jump up ^ Bies, David (2004). Engineering Noise Control, Theory and Practice. London: Spon Press. p. 235. ISBN 0-415-26713-7. As wind speed generally increases with altitude, wind blowing towards the listener from the source will refract sound waves downwards, resulting in increased noise levels.
Jump up ^ Cornwall, Sir (1996). Grant as Military Commander. New York: Barnes & Noble. p. 92. ISBN 1-56619-913-1.
Jump up ^ Cozens, Peter (2006). The Darkest Days of the War: the Battles of Iuka and Corinth. Chapel Hill: The University of North Carolina Press. ISBN 0-8078-5783-1.
Jump up ^ A B Wood, A Textbook of Sound (Bell, London, 1946)
Jump up ^ "Speed of Sound in Air". Phy.mtu.edu. Retrieved 13 June 2014.
Jump up ^ Nemiroff, R.; Bonnell, J., eds. (19 August 2007). "A Sonic Boom". Astronomy Picture of the Day. NASA. Retrieved 24 October 2010.
Jump up ^ Zuckerwar, Handbook of the speed of sound in real gases, p. 52
^ Jump up to: a b L. E. Kinsler et al. (2000), Fundamentals of acoustics, 4th Ed., John Wiley and sons Inc., New York, USA.
Jump up ^ J. Krautkrämer and H. Krautkrämer (1990), Ultrasonic testing of materials, 4th fully revised edition, Springer-Verlag, Berlin, Germany, p. 497
Jump up ^ "Speed of Sound in Water at Temperatures between 32–212 oF (0–100 oC) — imperial and SI units". The Engineering Toolbox.
Jump up ^ Wong, George S. K.; Zhu, Shi-ming (1995). "Speed of sound in seawater as a function of salinity, temperature, and pressure". The Journal of the Acoustical Society of America. 97 (3): 1732. Bibcode:1995ASAJ...97.1732W. doi:10.1121/1.413048.
Jump up ^ APL-UW TR 9407 High-Frequency Ocean Environmental Acoustic Models Handbook, pp. I1-I2.
Jump up ^ Robinson, Stephen (22 Sep 2005). "Technical Guides - Speed of Sound in Sea-Water". National Physical Laboratory. Retrieved 7 December 2016.
Jump up ^ "How Fast Does Sound Travel?". Discovery of Sound in the Sea. University of Rhode Island. Retrieved 30 November 2010.
^ Jump up to: a b Dushaw, Brian D.; Worcester, P. F.; Cornuelle, B. D.; Howe, B. M. (1993). "On Equations for the Speed of Sound in Seawater". Journal of the Acoustical Society of America. 93 (1): 255–275. Bibcode:1993ASAJ...93..255D. doi:10.1121/1.405660.
Jump up ^ Kenneth V., Mackenzie (1981). "Discussion of sea-water sound-speed determinations". Journal of the Acoustical Society of America. 70 (3): 801–806. Bibcode:1981ASAJ...70..801M. doi:10.1121/1.386919.
Jump up ^ Del Grosso, V. A. (1974). "New equation for speed of sound in natural waters (with comparisons to other equations)". Journal of the Acoustical Society of America. 56 (4): 1084–1091. Bibcode:1974ASAJ...56.1084D. doi:10.1121/1.1903388.
Jump up ^ Meinen, Christopher S.; Watts, D. Randolph (1997). "Further Evidence that the Sound-Speed Algorithm of Del Grosso Is More Accurate Than that of Chen and Millero". Journal of the Acoustical Society of America. 102 (4): 2058–2062. Bibcode:1997ASAJ..102.2058M. doi:10.1121/1.419655.
External links[edit]
Calculation: Speed of Sound in Air and the Temperature
Speed of sound: Temperature Matters, Not Air Pressure
Properties of the U.S. Standard Atmosphere 1976
The Speed of Sound
How to Measure the Speed of Sound in a Laboratory
Teaching Resource for 14-16 Years on Sound Including Speed of Sound
Technical Guides. Speed of Sound in Pure Water
Technical Guides. Speed of Sound in Sea-Water
Did Sound Once Travel at Light Speed?
Acoustic Properties of Various Materials Including the Speed of Sound
Technical Guides - Speed of Sound in Pure Water (provides a calculator for the speed in water)
Discovery of Sound in the Sea (uses of sound by humans and other animals)
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values: {\displaystyle R=8.314\,510~\mathrm {J/(mol\cdot K)} }

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Prehistoric medicine
From Wikipedia, the free encyclopedia
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For medicine in specific prehistoric societies, see Traditional Medicine.
This article needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. (April 2016) (Learn how and when to remove this template message)
A skull showing evidence of trepanning
Prehistoric medicine is any use of medicine from before the invention of writing and the documented history of medicine. Because the timing of the invention of writing varies per culture and region, the term "prehistoric medicine" encompasses a wide range of time periods and dates.[1]
The study of prehistoric medicine relies heavily on artifacts and human remains, and on anthropology. Previously uncontacted peoples and certain indigenous peoples who live in a traditional way have been the subject of anthropological studies in order to gain insight into both contemporary and ancient practices.[2]
Contents
[hide]
1 Disease and mortality
2 Treatments for disease
2.1 Plant materials
2.2 The use of earth and clays
2.3 Surgery
2.4 Magic and medicine men
3 Dentistry
4 The problem of evidence
5 See also
6 References
7 External links
Disease and mortality[edit]
Different diseases and ailments were more common in prehistory than today; there is evidence that many people suffered from osteoarthritis, probably caused by the lifting of heavy objects which would have been a daily and necessary task in their societies.[citation needed] For example, the transport of latte stones, though this practice only started during the neolithic era which involved hyper extension and torque of the lower back, while dragging the stones, may have contributed to the development of micro fractures in the spine and subsequent spondylolysis. Things such as cuts, bruises, and breakages of bone, without antiseptics, proper facilities, or knowledge of germs, would become very serious if infected, as they did not have sufficient ways to treat infection.[3][unreliable source?] There is also evidence of rickets, bone deformity and bone wastage (Osteomalacia),[4] which is caused by a lack of Vitamin D.
The life expectancy in prehistoric times was low, 25–40 years,[5] with men living longer than women; archaeological evidence of women and babies found together suggests that many women would have died in childbirth, perhaps accounting for the lower life expectancy in women than men. Another possible explanation for the shorter life spans of prehistoric humans may be malnutrition; also, men as hunters may have sometimes received better food than the woman, who would consequently have been less resistant to disease.[6]
Treatments for disease[edit]
Plant materials[edit]
Herbs such as rosemary may have been used for medicinal purposes by prehistoric peoples.[which?][7] [8] [9]
Plant materials (herbs and substances derived from natural sources)[10] were among the treatments for diseases in prehistoric cultures.[which?] Since plant materials quickly rot under most conditions, historians are unlikely to fully understand which species were used in prehistoric medicine. A speculative view can be obtained by researching the climate of the respective society and then checking which species continue to grow in similar conditions today[11] and through anthropological studies of existing indigenous peoples.[12][13] Unlike the ancient civilisations which could source plant materials internationally, prehistoric societies would have been restricted to localised areas, though nomadic tribes may have had a greater variety of plant materials at their disposal than more stationary societies.
The effects of different plant materials could have been found through trial and error.[14][unreliable source?] Gathering and dispensing of plant materials was in most cultures handled by women, who cared for the health of their family.[15] Plant materials were an important cure for diseases throughout history.[16] This fund of knowledge would have been passed down orally through the generations.
The birch polypore fungus, commonly found in alpine environments, may have been used as a laxative by prehistoric peoples living in Northern Europe, since it is known to bring on short bouts of diarrhoea when ingested, and was found among the possessions of a mummified man.[17]
The use of earth and clays[edit]
Earths and clays may have provided prehistoric peoples with some of their first medicines. This is related to geophagy, which is extremely widespread among animals in the wild as well as among domesticated animals. In particular, geophagy is widespread among contemporary non-human primates.[18] Also, early humans could have learned about the use of various healing clays by observing animal behaviour. Such clay is used both internally and externally, such as for treating wounds, and after surgery (see below).[citation needed] Geophagy, and the external use of clay are both still quite widespread among aboriginal peoples around the world, as well as among pre-industrial populations.
Surgery[edit]
Trepanning (sometimes Trephining) was a basic surgical operation carried out, predominantly by medicine men, in prehistoric societies across the world,[19][20] although evidence shows a concentration of the practice in Peru.[16][19][21] Several theories question the reasoning behind trepanning; it could have been used to cure certain conditions such as headaches and epilepsy.[22][23] These might have been considered effects of an evil spirit trapped within a person. Despite it being medically inappropriate in the vast majority of cases and a very dangerous procedure[citation needed] there is evidence discovered of bone tissue surrounding the surgical hole partially grown back, so therefore survival of the procedure did occur at least on occasion.[16]
The plate of skull bone, sometimes as large as 5 cm (2 in) in diameter, would have been kept with the person until their death, serving as a charm or in some spiritual or religious capacity; burial of this bone plate was thought to return the body to its full state for the afterlife.[citation needed] Trepanning is amongst few surgical operations to be carried out in prehistoric times;[citation needed] other surgery was rarely undertaken; medicine men had neither the training or the specialised equipment required to do surgery on the internal body. The procedure would have taken around 60 minutes in a single session, and if done in several sessions, it could have taken up to 12 days to complete.
Many prehistoric peoples,[which?] where applicable (geographically and technologically), were able to set broken or fractured bones using clay materials. An injured area was covered in clay, which then set hard so that the bone could heal properly without interference.[1] Also, primarily in the Americas, the pincers of certain ant species were used to close up wounds from infection; the ant was held above the wound until it bit, where its head would be removed allowing the pincers to remain and hold closed the wound.[24]
Magic and medicine men[edit]
Yup'ik shaman exorcising evil spirits from a sick boy.[25]
Main articles: Medicine man and Shamanism
Medicine men (also witch-doctors, shamans) maintained the health of their tribe by gathering and distributing herbs, performing minor surgical procedures,[26] providing medical advice, and supernatural treatments such as charms, spells, and amulets to ward off evil spirits.[27] In Apache society, as would likely have been the case in many others, the medicine men initiate a ceremony over the patient, which is attended by family and friends. It consists of magic formulas, prayers, and drumming. The medicine man then, from patients' recalling of their past and possible offenses against their religion or tribal rules, reveals the nature of the disease and how to treat it.
They were believed by the tribe to be able to contact spirits or gods and use their supernatural powers to cure the patient, and, in the process, remove evil spirits. If neither this method nor trepanning worked, the spirit was considered too powerful to be driven out of the person.[citation needed] Medicine men would likely have been central figures in the tribal system, because of their medical knowledge and because they could seemingly contact the gods. Their religious and medical training were, necessarily, passed down orally.[28]
Dentistry[edit]
Archaeologists in Mehrgarh in Balochistan province in the present day Pakistan discovered that the people of Indus Valley Civilization from the early Harappan periods (c. 3300 BC) had knowledge of medicine and dentistry. The physical anthropologist who carried out the examinations, Professor Andrea Cucina from the University of Missouri, made the discovery when he was cleaning the teeth from one of the men. Later research in the same area found evidence of teeth having been drilled dating to 7,000 B.C.E.[29]
The problem of evidence[edit]
There is no written evidence which can be used for investigation into the prehistoric period of history by definition. Historians must use other sources such as human remains and anthropological studies of societies living under similar conditions. A variety of problems arise when the aforementioned sources are used.
Human remains from this period are rare and many have undoubtedly been destroyed by burial rituals or made useless by damage.[30][31] The most informative archaeological evidence are mummies, remains which have been preserved by either freezing or in peat bogs;[32][33] no evidence exists to suggest that prehistoric people mummified the dead for religious reasons, as Ancient Egyptians did. These bodies can provide scientists with subjects' (at the time of death): weight, illnesses, height, diet, age, and bone conditions,[34] which grant vital indications of how developed prehistoric medicine was.
Not technically classed as 'written evidence', prehistoric people left many kinds of paintings, using paints made of minerals such as lime, clay and charcoal, and brushes made from feathers, animal fur, or twigs on the walls caves. Although many of these paintings are thought to have a spiritual or religious purpose,[35] there have been some, such as a man with antlers (thought to be a medicine man), which have revealed some part of prehistoric medicine. Many cave paintings of human hands have shown missing fingers (none have been shown without thumbs), which suggests that these were cut off for sacrificial or practical purposes, as is the case among the Pygmies and Khoikhoi.[36]
The writings of certain cultures (such as the Romans) can be used as evidence in discovering how their contemporary prehistoric cultures practiced medicine. People who live a similar nomadic existence today have been used as a source of evidence too, but obviously there are distinct differences in the environments in which nomadic people lived; prehistoric people who once lived in Britain for example, cannot be effectively compared to aboriginal peoples in Australia, because of the geographical differences.[37]
See also[edit]
Primitive skills
Sweat lodge
Mellified Man
Bush medicine
Mummia
Human fat
Venus of Willendorf
Anthropology
Paleolithic diet
References[edit]
^ Jump up to: a b Kelly, Nigel; Rees, Bob; Shuter, Paul (2003). Medicine Through Time. Heinemann. ISBN 978-0-435-30841-4.
Jump up ^ "Traditional Medicine". World Health Organization. Retrieved 2015-12-30.
Jump up ^ "The History of Medicine, Pre-history". Student reference and support materials. St Boniface's College. Retrieved 2009-02-19.
Jump up ^ "Babylon to Birmingham, A short journey through medicine to the end of the 18th Century". Revolutionary Players. History West Midlands. Retrieved 2015-12-30.
Jump up ^ Schools History Project (26 September 1996). Medicine & Health Through Time: an SHP Development Study. Hodder Education. ISBN 978-0719552656.
Jump up ^ "Prehistoric Medicine". HealthGuidance.Org. Retrieved 2009-02-19.
Jump up ^ Browning, Marie (1999). Natural Soapmaking. Sterling Publishing. p. 128. ISBN 0-8069-6289-5.
Jump up ^ "Aboriginal Plant Use in SE Australia". Australian Government, Australian National Botanic Gardens. Archived from the original on 2015-05-13. Retrieved 2015-12-30.
Jump up ^ "Medical use of Spices". UCLA Library, History and Special collections. Retrieved 2009-02-19.
Jump up ^ "Use Of Spices As Medicines". UCLA Library, History and Special collections. Retrieved 2009-02-19. Mentions spices being used by some prehistoric cultures
Jump up ^ Lock, Robin (2002). Plants of the Humid Tropics Biome. Eden Project books. p. 128. ISBN 978-1-90391913-2.
Jump up ^ Moerman, Daniel E. (2009). Native American Medicinal Plants: an ethnobotanical dictionary. Portland, OR / London: Timber Press. ISBN 978-0-88192-987-4.
Jump up ^ "Native American Herbal Remedies". Cherokee Messenger. Cherokee Cultural Society of Houston. 1996. Retrieved 2009-02-19.
Jump up ^ Schools History Project. "BBC - GCSE Bitesize, Prehistoric Civilisation". GCSE Bitesize. BBC. They have done this through a process of trial and error and natural selection.
Jump up ^ Hobbs, Christopher. "Herbal Medicine: An Outline of The History of Herbalism An Overview and Literature Resource List". healthy.net. HealthWorld Online. Retrieved December 30, 2015. ... women prepared food and healing potions--women generally practiced herbalism on a day to day basis, taking care of the ills of other members of the family or tribal unit
^ Jump up to: a b c "Primitive Medicine". HistoryWorld. Retrieved December 30, 2015.
Jump up ^ Wilford, John Noble (December 8, 1998). "Lessons in Iceman's Prehistoric Medicine Kit". The New York Times. New York. Retrieved December 30, 2015.
Jump up ^ Krishnamani, R.; Mahaney, William C. (2000). "Geophagy among primates: Adaptive significance and ecological consequences". Animal Behaviour. 59: 899–915. doi:10.1006/anbe.1999.1376.
^ Jump up to: a b "Pre-Columbian Trephination". NEUROSURGERY://ON-CALL/Cyber Museum of Neurosurgery. American Association of Neurological Surgeons and Congress of Neurological Surgeons. Retrieved 2009-02-19.
Jump up ^ Piek J, Lidke G, Terberger T, von Smekal U, Gaab MR (July 1999). "Stone age skull surgery in Mecklenburg-Vorpommern: a systematic study". Neurosurgery. 45 (1): 147–51; discussion 151. PMID 10414577. doi:10.1097/00006123-199907000-00033. A small but informative text
Jump up ^ "Trephination, An Ancient Surgery". UIC Oral Sciences OSCI 590: Hominid Evolution, Dental Anthropology, and Human Variation. University of Illinois at Chicago. Archived from the original on March 3, 2016. Retrieved December 30, 2015. In Peruvian practice there is considerable evidence that many of the operations were performed for the naturalistic purpose of removing a bone fragment ... and trephination undertaken as a supernatural curative procedure by shamans (sancoyoc) with little technical ability as surgeons.
Jump up ^ Siegfried, Juliette. "History of Brain Surgery". Brain-Surgery.com. Retrieved December 30, 2015.
Jump up ^ Osler, Sir William (1922). The Evolution of Modern Medicine: A Series of Lectures Delivered at Yale University on the Silliman Foundation in April, 1913. New Haven: Yale University Press. pp. 6–9. See the section "Origin Of Medicine"
Jump up ^ Gudger, E. W. (1925). "Stitching Wounds With the Mandibles of Ants and Beetles". J. Amer. Med. Assoc. 84: 1861–4.
Jump up ^ Fienup-Riordan, Ann (1994). Boundaries and Passages: Rule and Ritual in Yup'ik Eskimo Oral Tradition. Norman, OK: University of Oklahoma Press. ISBN 0-585-12190-7.
Jump up ^ "Mysteries of Africa". Encounter South Africa. Encounter Magazine. Retrieved December 30, 2015. Stories of Medicine Men in Africa
Jump up ^ Ackerknecht, Erwin Heinz (1982) [1955]. A Short History of Medicine (Johns Hopkins Paperbacks ed.). Baltimore: Johns Hopkins University Press. ISBN 0-8018-2726-4.
Jump up ^ "Healing Secrets of Aboriginal Bush Medicine". Big River Internet. Retrieved December 30, 2015. Trained from an early age by their elders and initiated into the deepest of tribal secrets...
Jump up ^ "Stone age man used dentist drill". BBC News. 2006-04-06. Retrieved 2010-05-22.
Jump up ^ Coulson, Ian. "Prehistoric Medicine In Kent". The History of Health and Medicine in Kent. Kent County Council. Archived from the original on December 2, 2008. Retrieved December 30, 2015. It is a matter of luck because only some skeletons survive
Jump up ^ WP:CIRCULAR Wikipedia's Ötzi the Iceman Article '..three or four of his right ribs had been squashed when he had been lying face down after death, or where the ice had crushed his body.'
Jump up ^ Mystery of the Mummies, Five Documentary
Jump up ^ Malam, John (2001). Secret Worlds: Mummies, and the Secrets of Ancient Egypt. Megabites. DK Children. ISBN 978-0-78947976-1.
Jump up ^ WP:CIRCULAR Wikipedia's Article on the Mummy Juanita
Jump up ^ Ganeri, Anita; Martell, Hazel Mary; Williams, Brian (2007). World History Encyclopedia: A Complete and Comprehensive Guide to the History of the World. Parragon. ISBN 978-1-40549120-4.
Jump up ^ Janssens PA (October 1957). "Medical Views on Prehistoric Representations of Human Hands". Med Hist. 1 (4): 318–22. PMC 1034309  . PMID 13476920. doi:10.1017/s0025727300021499. Pages 318–21 are of particular interest in this subject
Jump up ^ "Prehistoric Medicine". History GCSE / History of Medicine Lessons. Education Forum. Retrieved December 2015. Check date values in: |access-date= (help)
External links[edit]
Sem, Tatyana. "Shamanic Healing Rituals". Russian Museum of Ethnography.
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This page was last edited on 20 September 2017, at 16:23.
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values: طب ما قبل التاريخ – Arabic

values: Medicina na prehistoria y la protohistoria – Asturian

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