Singing Rod

A metal rod can be made to resonate and "sing" by striking or rubbing it at specific points. By holding the rod at different positions, students can hear the fundamental tone or overtones, illustrating resonance, nodes, and antinodes in standing waves.

Part 1: Resonance by Striking

1. Hold a metal rod at its midpoint.
2. Strike one end against a table or tap it with a hammer.
3. Listen for the clear fundamental tone.
4. Hold the rod at one-quarter of its length and strike again.
5. Observe the change in pitch due to the overtone.
6. Try holding the rod at different positions to explore resonance and damping.

Part 2: Singing Rod by Rubbing

1. Hold the rod loosely at its midpoint.
2. Rub the length of the rod with fine sandpaper until it begins to resonate.
3. Adjust the pace of rubbing to achieve a sustained “singing” sound.
4. Experiment by holding the rod at one-quarter length and rubbing again to produce a higher-pitched overtone.
5. Ask students where the sound originates and how to stop the vibrations.

Singing Rod Demo - College Physics with Greg Francis:

Singing Rod - A Cool Vibration Trick - Sick Science!:

📄 Singing rod - Ad Mooldijk & Norbert van Veen: https://interactivetextbooks.tudelft.nl/showthephysics/demos/demo81/demo81.html

• Compare rods of different materials (aluminum vs brass) and lengths.
• Use a hammer instead of sandpaper to excite vibrations.
• Record frequencies with a smartphone spectrum analyzer (e.g., phyphox).

• Ensure the rod is held firmly to avoid dropping it.
• Keep the sound duration short, as high-pitched tones can be uncomfortable.

• Why does holding the rod at the midpoint produce the fundamental tone? (It creates a node at the center and antinodes at the ends.)
• What changes when you hold the rod at one-quarter length? (It produces the first overtone, an octave higher.)
• Is the vibration longitudinal or transverse? (Both can occur; damping the rod differently reveals each type.)
• How can the speed of sound in the rod be calculated from its frequency and length? (Using the relationship between wavelength, frequency, and wave speed.)