A longitudinal standing wave can be created in a long, thin aluminum rod by stroking the rod with very dry fingers. This is often done as a physics demonstration, creating a high-pitched, very annoying whine. From a wave perspective, the standing wave is equivalent to a sound standing wave in an open-open tube. In particular, both ends of the rod are anti-nodes. (Figure 1)
The Attempt at a Solution
The problem is that I don't know how to calculate the speed of sound in an aluminum rod. I've ran across only one similar problem where they used:
f = v / 2 L ; where v = speed of sound
So we need to find the speed of sound in aluminum. See second web site.
f = (4877 m/s) / (2∙1.90m)
f = 128.2 s^-1 = 128.2 Hz
they then used this link to find the speed of sound in a aluminum rod