Lesson 1 Objective

At the end of this section, you should be able to:

• define superposition principle;
• explain how standing waves are formed;
• define interference of waves.
• define terms like loudness, pitch, and timbre (quality);

Brainstorming Question

What is the difference between louder and quieter sounds, or higher pitch and lower pitch sounds? Why does the same note sound different from a violin to a piano?

key terms and concepts

• Superposition: Waves combine to create constructive (amplified) or destructive (canceled) interference.
• Standing Waves: Result from two opposite direction waves, forming stationary nodes and antinodes.
• Pitch: Higher frequency = higher pitch.
• Loudness: Greater amplitude = louder sound (measured in dB).
• Timbre: Differentiates sound sources.

Superposition of Waves

When two or more waves pass through the same point simultaneously, their combined displacement is the sum of their individual displacements. This is called the superposition principle. Superposition leads to interference, which can be constructive (waves in phase amplify each other) or destructive (waves out of phase cancel each other).

Standing Waves

Standing waves are formed when two identical waves travel in opposite directions and interfere in a medium, creating fixed points called nodes (zero displacement) and antinodes (maximum displacement). These waves appear stationary, like a vibrating guitar string.

Figure 6.5 Superposition of two identical waves results in a standing wave

Simulation

Standing Wave Synthesis

Characteristics of Sound Waves

Sound cannot travel through a vacuum. The movement of molecules of a medium is essential for the propagation of sound waves. The characteristics of sound are:

• Pitch: Depends on the frequency of the sound wave; higher frequency means higher pitch.
• Loudness: Depends on the amplitude of the sound wave; greater amplitude means louder sound, measured in decibels (dB).
• Timbre (Quality): Distinguishes sounds with the same pitch and loudness but produced by different sources, like different musical instruments.