Il 16 Giu 2005, 09:08, "Mino Saccone" <mino.saccone_at_fastwebnet.it> ha
scritto:
>
>
> Sara' meglio che ti ristudi un po' l'argomento.
>
> Anche senza libri, basta un brevissima ricerca su Google
>
Puoi controllare anche qui:
http://en.wikipedia.org/wiki/Sound_speed
Da cui riporto il seguente:
<cit.>
In a Non-Dispersive Medium � Sound speed is independent of frequency,
therefore the speed of energy transport and sound propagation are the same.
Air is a non-dispersive medium.
In a Dispersive Medium � Sound speed is a function of frequency. The spatial
and temporal distribution of a propagating disturbance will continually
change. Each frequency component propagates at each its own phase speed,
while the energy of the disturbance propagates at the group velocity. Water
is an example of a dispersive medium.
In general, the speed of sound c is given by
c=sqrt(C/rho)
where
C is a coefficient of stiffness
rho is the density
Thus the speed of sound increases with the stiffness of the material, and
decreases with the density.
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=sqrt(K/rho)
where
K is the adiabatic bulk modulus
For a gas, K is approximately given by
K=k*p
where
� is the adiabatic index, sometimes called �.
p is the pressure.
Thus, for a gas the speed of sound can be calculated using:
c=sqrt(k*p/rho)
which using the ideal gas law is identical to:
c=sqrt(krT)
(Newton famously used isothermal calculations and omitted the � from the
numerator.)
In a solid, there is a non-zero stiffness both for volumetric and shear
deformations. Hence, in a solid it is possible to generate sound waves with
different velocities dependent on the deformation mode.
In a solid rod (with thickness much smaller than the wavelength) the speed
of sound is given by:
c=sqrt(E/rho)
where
E is Young's modulus
� (rho) is density
Thus in steel the speed of sound is approximately 5100 m/s.
<cit.>
Da questa si vede quanto che quanto ho detto e' corretto.
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Received on Thu Jun 16 2005 - 10:09:20 CEST