Speed Of Sound In Aluminum


To compare the measured and the theoretical values of the speed of sound in aluminum.


Stroked aluminum rod demo, oscillator, digital frequency meter, 2-meter stick.

Setup Time

5 min.




An aluminum rod is stroked (See Demonstration H3-71: STROKED ALUMINUM ROD.), setting up longitudinal standing waves in the rod. The frequency f is determined using a frequency meter, with or without the aid of an audio oscillator. The length L of the rod, one-half wavelength for the fundamental, is measured using a two-meter rule. The speed of sound in aluminum is then s = 2fL. The theoretical value is obtained by using the bulk modulus B and the mass density d: s=SQRT( B/d), where the bulk modulus B=7.8x10^+10 Pa and the density of aluminum d=2.699x10^+3 kg/m.


Oakes Ames, A Direct Measurement of the Speed of Sound in Rods, AJP 38, 1151-1152 (1970).