lavster said:
What factors affect the speed of sound besides the temperature? Does viscosity affect the speed of sound?
Thanks
lavster, Yes, viscosity does affect the speed of sound in fluids. Here are some websites that may illuminate the mechanism:
Just to be sure we all use accepted terms, I post these two Wikipedia excerpts:
“Viscosity is a measure of the resistance of a fluid which is being deformed by either shear stress or tensile stress. In everyday terms (and for fluids only), viscosity is "thickness" or "internal friction". Thus, water is "thin", having a lower viscosity, while honey is "thick", having a higher viscosity. Put simply, the less viscous the fluid is, the greater its ease of movement (fluidity).[1]
Kinematic viscosity
In many situations, we are concerned with the ratio of the inertial force to the viscous force (i.e. the Reynolds number, ), the former characterized by the fluid density ρ. This ratio is characterized by the kinematic viscosity (Greek letter nu, ν), defined as follows:
The SI unit of ν is m2/s. The SI unit of ρ is kg/m3.
The cgs physical unit for kinematic viscosity is the stokes (St), named after George Gabriel Stokes. It is sometimes expressed in terms of centistokes (cSt). In U.S. usage, stoke is sometimes used as the singular form.
1 St = 1 cm2•s−1 = 10−4 m2•s−1.
1 cSt = 1 mm2•s−1 = 10−6m2•s−1.
Water at 20 °C has a kinematic viscosity of about 1 cSt.
The kinematic viscosity is sometimes referred to as diffusivity of momentum, because it is analogous to diffusivity of heat and diffusivity of mass. It is therefore used in dimensionless numbers which compare the ratio of the diffusivities.”
http://en.wikipedia.org/wiki/Viscosity#Kinematic_viscosity
"Volume viscosity (also called bulk viscosity or second viscosity) becomes important only for such effects where fluid compressibility is essential. Examples would include shock waves and sound propagation."
http://en.wikipedia.org/wiki/Volume_viscosity
“The speed of sound in air and other gases, liquids, and solids is predictable from their density and elastic properties of the media (bulk modulus).
The bulk modulus of a solid influences the speed of sound and other mechanical waves in the material.”
http://hyperphysics.phy-astr.gsu.edu/hbase/sound/souspe2.html
Just as is shown by the above, the speed of sound in fluids (gasses and liquids) is dependent on density and bulk modulus (Hooke's Law). The bulk modulus of a substance measures the substance's resistance to uniform compression.
Now, this appears in Encyclopedia Britannica:
“...(in the direction of the wave) is a combination of a uniform compression and a shearing stress (a force that causes one plane of a substance to glide past an adjacent plane). Hence, both bulk and shear viscosity also govern the propagation of sound in a liquid.”
http://www.britannica.com/EBchecked/topic/124117/coefficient-of-viscosity
In order to read that article one needs to join and pay. This is frustrating to say the least. I hesitate to pay just to learn some basic science.
This article clearly states that viscosity does affect the sound velocity in liquids:
S Parthasarathy and N N Bakhshi 1953 Proc. Phys. Soc. B 66 368 doi:10.1088/0370-1301/66/5/303
“Relation between Velocity of Sound and Viscosity in Liquids”
Abstract:
A new relationship, viz. v1/3/ρ = A + B/η1/2, between sound velocity v, viscosity η and density ρ of a liquid, has been obtained. It is observed that A is a constant (=13.56) for all the homologous series considered, whereas B is different for different series. A plot of v1/3/ρ against 1/η1/2 gives a set of straight lines diverging from the same point on the y-axis (0, 13.56)."
http://iopscience.iop.org/0370-1301/66/5/303"Longitudinal rheology. Bulk Viscosity and Longitudinal Viscosity
Propagation of a longitudinal stress wave through a visco-elastic media creates dissipation of mechanical energy, similarly to a shear stress wave. The rate of dissipation depends on two parameters: bulk viscosity and longitudinal viscosity. For Newtonian liquid it is bulk viscosity that is analog to the dynamic viscosity for the shear stress. For non-Newtonian liquid it is longitudinal viscosity, analog to the shear viscosity for the shear rheology.
Measurement of ultrasound attenuation is the only known way of characterizing these parameters for both Newtonian and non-Newtonian liquids. Our Acoustic sensor allows very precise measurement of the ultrasound attenuation. It is important to perform this measurement at different frequencies. Frequency dependences allow resolving between bulk viscosity and longitudinal viscosity.
For more details read:
Dukhin, A.S. and Goetz, P.J. " Bulk viscosity and compressibility measurement using acoustic spectroscopy," The Journal of Chemical Physics, Vol.130, Issue 12, (2009)"
http://www.dispersion.com/bulk-viscosity.html
Sound Speed and Kinematic Viscosity Table
https://sites.google.com/a/trcorpor...868/Sound-Speed-and-Kinematic-Viscosity-Table
