A guitar string is plucked under a strobe light to make its vibration appear frozen or moving in slow motion. By adjusting the strobe frequency, students can observe nodes, antinodes, and harmonic patterns that are normally too fast to see.

1. Set up a guitar in a darkened room so the strings are clearly visible.
2. Position a strobe light so it illuminates the strings directly.
3. Pluck a guitar string gently to set it vibrating.
4. Adjust the strobe frequency:
   1. If the strobe flashes at the same frequency as the string vibration, the string appears stationary.
   2. If the strobe frequency is slightly higher or lower, the string appears to move slowly back and forth (apparent motion).
5. Observe the stationary wave pattern with nodes (points of no motion) and antinodes (points of maximum motion).
6. Repeat with different strings and different notes to compare patterns and frequencies.

Close up view of guitar string vibrations using a stobe light - VideoHistoryToday:

Standing Waves and the Strobe Effect - SMUPhysics

• Use a phone strobe app instead of a laboratory strobe light.
• Compare fundamental frequency vs harmonics by lightly touching the string at the midpoint or other fractional lengths.
• Try with other stringed instruments (violin, ukulele, bass) for comparison.
• Record the demonstration with a slow-motion camera as an alternative to a strobe.

• Do not stare directly into the strobe light—prolonged exposure can cause discomfort or trigger seizures in sensitive individuals.
• Use the strobe only in short demonstrations.
• Ensure the guitar is stable so it does not fall when plucked under low lighting conditions.

• Why does the string appear still under the strobe light? (Because the strobe flashes in sync with the vibration frequency, creating the illusion of no motion.)
• What happens when the strobe frequency is slightly different from the string’s vibration frequency? (The string appears to move slowly, a visual “beat” effect.)
• How can this demonstration help visualize standing waves on strings? (It makes nodes and antinodes visible, showing how harmonics form.)
• How does string length, thickness, and tension affect the observed frequency? (Shorter, thinner, tighter strings vibrate at higher frequencies, producing higher pitches.)