Sound and Waves

Vibration

The cyclical motion of an object about an equilibrium poin

Mechanical wave

The transfer of energy through a material due to vibratio

Medium

The material that permits the transmission of energy through vibrations

Net Motion

The displacement of a particle over a certain time interval; the difference between the particle’s initial and final positions

Elastic

The property of a medium that returns to its original shape after being disturbed

Transverse wave

A wave in which particles vibrate perpendicular to the direction of the flow of energy

Longitudinal wave

A wave in which particles vibrate parallel to the direction of the flow of energy

Compression

The region in a longitudinal wave in which the medium’s particles are

closer together

Rarefaction

The region in a longitudinal wave in which the medium’s particles are

farther apart

Sound

A form of energy produced by rapidly vibrating objects detectable by

sensory organs such as the ear

Amplitude

The maximum displacement of a wave from its equilibrium poin

Waveform

The shape of a wave when graphed

Crest

The maximum point of a transverse wave

Trough

The minimum point of a transverse wave

wavelength

the distance between two similar points in successive identical cycles in a wave, such as from crest to crest or trough to trough

Phase

In a continuous transverse or longitudinal wave, the x-coordinate of a

unique point of the wave

Phase shift

A shift of an entire wave along the x-axis with respect to an

otherwise identical wave

Frequency

The number of complete cycles that occur in unit time, usually 1 s; measured in hertz (Hz)

Period

The time for a vibrating particle to complete one cycle

Wave speed

The rate at which a wave is travelling through a medium; also a measure of how fast the energy in the wave is moving

Simple harmonic motion

Any motion that repeats itself at regular interval

Linear density

The mass per unit distance of a string; units are kilograms per meter

Audible sound wave

Sound wave in the range of human hearing, 20 Hz to 20 kHz

Infrasonic wave

Sound wave with a frequency below 20 Hz

Ultrasonic wave

Sound wave with a frequency above 20 kHz

Mach number

The ratio of the airspeed of an object to the local speed of sound

Pressure

The force per unit area

Sound intensity

The amount of sound energy being transferred per unit area; unit W/m²

Decibel

The unit of sound level used to describe sound intensity level

Free-end reflection

A reflection that occurs at a media boundary where the second medium is less dense than the first medium; reflections have an amplitude with the same orientation as the original wave

beat

Periodic change in sound intensity caused by the interference between two nearly identical sound waves

Fixed-end reflection

A reflection that occurs at a media boundary where one end of the medium is unable to vibrate; reflections are inverte

Transmission

The motion of a wave through a medium, or motion of a wave from one medium to another medium

Standing wave

An interference pattern produced when incoming and reflected waves interfere with each other; the effect is a wave pattern that appears to be stationary

Node

In a standing wave, the location where the particles of the medium are at rest

Antinode

In a standing wave, the location where the particles of the medium are moving with the greatest speed; the amplitude will be twice the amplitude of the original wave

fundamental frequency or first harmonic

the lowest frequency that can produce a standing wave in a given medium

Harmonics

Whole-number multiples of the fundamental frequency

Overtone

A sound resulting from a string that vibrates with more than one frequency

beat frequency

produced by the interference of two waves with slightly different frequencies; equal to the difference in the frequencies of the interfering waves

Damping

A reduction in the amplitude of a wave as a result of energy absorption or destructive interference

Resonant frequency

the frequency at which a medium vibrates most easily

resonance

the condition in which the frequency of a wave equals the resonant frequency of the wave’s medium

Doppler effect

When a source of sound approaches an observer, the observed frequency of the sound increases; when the source moves away from an observer, the observed frequency of the sound decreases