# Stationary Waves

## Basic Principle

• A stationary wave is a wave where points within the wave, known as nodes, experience zero displacement because the two waves that make up the stationary wave are completely out of phase.
• These stationary waves are created by superposition of two waves which have equal frequency and amplitude but are travelling in opposite directions.
• These waves occur commonly in musical instruments, with the length of the stationary wave determining the note heard.

## Nodes and Antinodes

• Nodes are the points of zero amplitude along the wave. They occur where the two waves are out of phase and hence cancel each other out.
• Antinodes are the points of maximum amplitude along the wave. They occur where the two waves are in phase and hence their displacements combine to give maximum displacement.

# Resonance

## Basic Principle

• Resonance is a phenomenon that occurs when an object is made to vibrate at its natural frequency, resulting in an increase in amplitude.
• This large displacement is often realised through the regular, periodic application of an external force.

## Applications

• In musical instruments, a musician creates resonance by applying a regular force (for example, by plucking a guitar string or blowing into a wind instrument) at the natural frequency of the instrument or part of the instrument.
• Resonance can cause large displacements and so can be destructive, as in the case when soldiers marching in step can cause a bridge to collapse, or beneficial, as in the case of a microwave oven where resonance with water molecules heats food.

Remember that understanding the concept of Stationary Waves and Resonance is key in understanding other wave properties such as wave speed, velocity, and frequency, practical applications of sound in technology and the natural world, and principles of acoustics and music.