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ID Code: H1-23
Purpose: 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 Young's modulus Y and the mass density d: S = SQRT(Y/d), where the Young's modulus Y=7.0x10^+10 Pa and density of aluminum d=2.699x10^+3 kg/m^3. Putting in numbers, S = SQRT(Y/d) = 5,093 m/s. For the first mode of the stroked rod, the wavelength is twice the length of the rod, so measuring the length of the rod L = 1.83m, and the frequency of the first mode f = 1370 Hz, the speed of sound in aluminum is S = 2fL = 5,014 m/s.
Availability: Available