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

**DESCRIPTION: **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.

**SUGGESTIONS: **

**REFERENCES: ** (PIRA
unavailable.)

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

**SETUP TIME: **5 min.