Lecture Notes: Crash Course on the Physics of Musical Instruments

Introduction

• Theme music introduction.
• Exploration of how musical instruments like guitars create music.
• Discussion on the science of sound and sound waves in music.

Sound Waves

• Sound as a Longitudinal Wave: Medium oscillates in the same direction as wave movement.
• Standing Waves: Special waves that appear stationary, with changing amplitude.

Mechanisms of Sound in Instruments

• String Instruments: Sound created by vibrating strings in air.
• Wind and Brass Instruments: Utilize standing waves for sound production.

Standing Waves

• Result of reflection and interference.
  • Reflection: Wave reaches end, moves back along the path.
  • Interference: Peaks pass each other, change sizes, create a wave that appears stationary.
• Anatomy: Nodes (no oscillation) and Antinodes (max oscillation).

String Instrument Physics

• Fixed Ends: Strings with fixed ends create nodes at ends.
  • Fundamental Wave: Simplest wave; 1st harmonic, fewest nodes and antinodes.
  • Overtones: Build on fundamental, add nodes and antinodes.
  • Harmonics: Fundamental and overtones together.

Wavelength and Frequency

• Wavelength: Number of wavelengths is equal to the number of harmonic divided by 2.
• Frequency: Related to velocity and wavelength.
  • Fundamental frequency = velocity / (2 x string length).
  • Harmonic frequency = harmonic number x fundamental frequency.

Application to Instruments

• Piano and Guitar: Strings tuned to fundamental frequencies for notes.
• Flute: Pipes with open ends behave differently.
  • Fundamental wave has antinodes at ends.

Pipes with One Closed End

• Pan Flutes: One end closed, one open.
  • Closed end = node, open end = antinode.
  • Fundamental spans quarter wavelength.
  • No even-numbered harmonics possible.

Conclusion

• Discussed standing waves, harmonics, and how they determine frequency.
• Differences in sound among instruments explained by harmonics.

Additional Information

• PBS Digital Studios: Related shows and content.
• Production Credits: Filmed in the Doctor Cheryl C. Kinney Crash Course Studio with Thought Cafe graphics team.