Glossary
Amplitude Variations
Changes in the maximum displacement or intensity of a wave, often resulting from the interaction of multiple waves.
Example:
The loud and soft spots you hear when two slightly detuned instruments play together are examples of amplitude variations caused by beats.
Antinodes
Points along a standing wave where the displacement or amplitude is maximum, experiencing the greatest motion.
Example:
The widest part of a vibrating jump rope, where it swings the most, represents an antinode.
Beat Frequency
The frequency at which the amplitude of a beat pattern varies, equal to the absolute difference between the frequencies of the two interfering waves.
Example:
If one tuning fork is 440 Hz and another is 442 Hz, the beat frequency you hear will be 2 Hz.
Beats
Periodic variations in the amplitude of a sound wave, produced when two waves of slightly different frequencies interfere.
Example:
When two tuning forks with nearly identical frequencies are struck, you hear a pulsating sound, which are beats.
Constructive Interference
Occurs when two waves overlap in phase, resulting in a resultant wave with an amplitude greater than or equal to the sum of the individual amplitudes.
Example:
When two crests of water waves meet, they combine to form a larger crest due to constructive interference.
Destructive Interference
Occurs when two waves overlap out of phase, resulting in a resultant wave with an amplitude smaller than the individual amplitudes, potentially zero.
Example:
Noise-canceling headphones work by producing sound waves that undergo destructive interference with incoming ambient noise.
Fundamental (Frequency/Harmonic)
The lowest possible resonant frequency of a vibrating system, corresponding to the simplest standing wave pattern.
Example:
The lowest note you can play on a wind instrument corresponds to its fundamental frequency.
Harmonics
Frequencies that are integer multiples of the fundamental frequency, producing more complex standing wave patterns.
Example:
A musician can play different harmonics on a string by lightly touching it at specific points, producing higher-pitched notes.
Incident Waves
A wave that strikes a boundary or interface, often leading to reflection or transmission.
Example:
When a sound wave hits a wall, the incident wave is the one approaching the wall before it bounces off.
Interference
The phenomenon that occurs when two or more waves overlap, resulting in a new wave pattern whose amplitude is the sum of the individual wave amplitudes.
Example:
When two ripples from dropped pebbles meet in a pond, they create a complex pattern of peaks and troughs due to wave interference.
Nodes
Points along a standing wave where the displacement or amplitude is always zero, experiencing no motion.
Example:
On a vibrating guitar string, the fixed ends and certain points in between are nodes, where the string doesn't move.
Open-Closed Tube
A tube or pipe that is open at one end and closed at the other, resulting in a standing wave with an antinode at the open end and a node at the closed end.
Example:
A clarinet behaves like an open-closed tube, where the reed end is effectively closed and the bell end is open.
Open-Open Tube
A tube or pipe that is open at both ends, allowing standing sound waves to form with antinodes at both openings.
Example:
A flute acts like an open-open tube, producing sound when air vibrates within it.
Reflected Waves
A wave that bounces off a boundary or interface, changing its direction of propagation.
Example:
An echo is created by a sound wave that has been a reflected wave off a distant surface.
Resonance
The phenomenon where a vibrating system responds with maximum amplitude to an external force or vibration at a specific frequency, typically its natural frequency.
Example:
A wine glass can shatter if a singer hits the right pitch, causing the glass to vibrate at its resonance frequency.
Standing Waves
A wave pattern that appears to remain in a fixed position, formed by the superposition of two identical waves traveling in opposite directions.
Example:
When you pluck a guitar string, it vibrates in a standing wave pattern, creating the musical note.
Superposition
The principle stating that when two or more waves overlap, the resultant displacement at any point and at any instant is the vector sum of the displacements of the individual waves at that point and instant.
Example:
Imagine two sound waves from different speakers reaching your ear; the sound you hear is the superposition of those two waves.
Traveling Waves
Waves that propagate through a medium, transferring energy from one point to another without the medium itself being transported.
Example:
A light wave from the sun traveling waves through space to reach Earth, carrying energy with it.
Wave Pulses
A single disturbance that travels through a medium, rather than a continuous wave train.
Example:
If you quickly flick one end of a rope, a single hump, or wave pulse, travels down its length.