PURPOSE: To illustrate resonance in an air column.

DESCRIPTION: Strike either tuning fork and hold it to the end of the tube. The sound intensity of the fork at the resonant frequency (480Hz) of the tube increases dramatically, whereas the fork with the non-resonant frequency (384Hz) does not become significantly louder. The second harmonic of the tube is excited (see fourth video below).

For videos of the sequential parts of this demonstration, click your mouse on the appropriate item below:

• tones produced by the two tuning forks.
• resonance of the 480Hz tuning fork with tube.
• lack of resonance of the 384 Hz tuning fork with the tube.
• Comparison of 480Hz tuning fork and blowing across tube.

SUGGESTIONS:

See Question of the Week #161 and Question of the Week #162 for information on using this demonstration to enhance class involvement.

REFERENCES: (PIRA unknown.)

EQUIPMENT: Plastic tube with resonant (right) and non-resonant (left) tuning forks.

SETUP TIME: None.