Sound Velocity of material

The speed of sound in air is around 768 mi/hr (1,125 ft/sec, 343m/sec), or about 5 seconds per mile, or 3 seconds per kilometer. That is the reason for the rule of thumb where when you see a flash of lightning, count the number of seconds until you hear the thunder clap, then divide by five. That gives you the approximate distance (in miles) away of the lightning. Divide by three for kilometers. Speed of sound very important for aplication to ultrasonic flow meter or ultrasonic level sensor.


The speed of sound in any medium is dependent upon the coefficient of stiffness (modulus of bulk elasticity for gas mediums). Density and/or compressibility alone does not determine the speed of sound.

  • Vl = Velocity of plane longitudinal wave in bulk material.

  • Vs = Velocity of plane transverse (shear) wave.

  • Vext = Velocity of longitudinal wave (extensional wave) in thin rods.

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