which is the velocity?

Sorry, I dunno anything about materials. I would like to know the formula to figure out the longitudinal and shear velocity in Glass
PYREX.
HEre the details: Material PYREX
Coefficient of Expansion (20°C – 300°C) 3.3 x 10-6 K-1 Density 2.23 g/cm3 Refractive index (Sodium D line) 1.474 Dielectric Constant (1MHz,20°C) 4.6 Specific heat (20°C) 750J/kg°C Thermal conductivity (20°C) 1.14W/m°C
Poisson's Ratio (25°C – 400°C) 0.2 Young's Modulus (25°C) 6400 kg/mm2
Refractive index (Sodium D line) = 1.474 Visible light transmission, 2mm thick glass = 92% Visible light transmission, 5mm thick glass = 91%
I used this equation:
symb bulk = \$young / ( 3. * ( 1. - 2. * \$poisson ) ) symb shear = \$young / ( 2. * ( 1. + \$poisson ) )
but doesn t work substituting this pascal conversion for the poisson ration of 9.8*10e6 kg/mm2= 1pascal. The bulk velocity is 348410e7 m/s!!!!!
2) is there any way to find out the attenuation in pyrex with my data? Please help me! Thanks a lot manuela
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tramoman wrote:

The poisson ratio is dimensionless..... it is not in Pascals. It is a ratio of lateral strain to axial strain and the units of strain are dimensionless themselves, and the ratio is also dimensionless.
Look at the definition of the terms to gain an understanding.
I haven't checked your equations, so I assume that they are right, but I quite fail to understand what is symb bulk.
And I don't see any equation there that seems to have the right units to compute velocity.
So, I suspect that you haven't googled the right equation for the sonic velocities.
When I googled "longitudinal velocity equation" all the equations were on links for the first results page, in the first few hits.
Are you a student at Stanford University?
> 2) is there any way to find out the attenuation in pyrex with my data?
No.
Jim
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"tramoman" wrote in message

There are many good books on basic material properties, even Google and Eric Weisstein would help.

Young's Modulus is defined as the ratio of stress over strain ((delta L/L) / (Force/Area)). So Young's Modulus has dimensions of pressure. The kg/mm^2, although a pretty term, does not have units of pressure. Areal density, yes, pressure, no.
Have a think about what units you want to work in and make the appropriate conversions. NB, 1 Pa = 1 Newton per square metre.

And where did they come from and did you understand their derivation? If not, then there's no point plugging in numbers with arbitrarily chosen units.

Nope. Have a think about that last line. 1 bar is about 1e5 Pa. 9.8 million kilogrammes resting on an area of 1mm x 1mm is a jolly high pressure. In any case, kg/area is not a pressure; had you said 1Pa is the pressure applied to the ground by a 1m x 1m sheet of stuff face down on the garage floor if that sheet has a mass of about 100 grammes, then you would be right.
Stick to metres, kilogrammes, and seconds and you won't go wrong, but you first have to understand what pressure means.
-James Garry
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James Garry wrote:

In the old days, the kilogram was used as a unit of force: the force corresponding to the gravitational force acting on a 1 kg mass at the surface of the earth. Usually this was written "kgf" (kilogram force) to distinguish it from the mass unit.
Dave Palmer
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Velocity and Acoustic Impedance table
Material Longitudinal
Velocity Shear
Velocity Acoustic Impedance
Air .013 .33 - - .0004
Aluminum .25 6.3 .12 3.1 17.0
Al. Oxide .39 9.9 .23 5.8 32.0
Beryllium .51 12.9 .35 8.9 23.0
Boron Carbide .43 11.0 - - 26.4
Brass .17 4.3 .08 2.0 36.7
Cadmium .11 2.8 .059 1.5 24.0
Copper .18 4.7 .089 2.3 41.6
Glass (crown) .21 5.3 .12 3.0 18.9
Glycerin .075 1.9 - - 2.42
Gold .13 3.2 .047 1.2 62.6
Ice .16 4.0 .08 2.0 3.5
Inconel .22 5.7 .12 3.0 47.2
` end
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