Chapter 17: Mechanical Waves and Sound

Comprehensive vocabulary flashcards covering mechanical wave types, properties, behaviors, and the physics of sound and hearing from the Chapter 17 lecture notes.

Mechanical Wave

A disturbance in matter that carries energy from one place to another.

Medium

The material through which a mechanical wave travels.

Transverse Wave

A wave that causes the medium to vibrate at right angles to the direction in which the wave travels.

Crest

The highest point of a transverse wave.

Trough

The lowest point of a transverse wave.

Longitudinal Wave

A wave in which the vibration of the medium is parallel to the direction the wave travels.

Compression

An area in a longitudinal wave where the particles in a medium are spaced close together.

Rarefaction

An area in a longitudinal wave where the particles in a medium are spread out.

Surface Wave

A wave that travels along a surface separating two media, where particles move in a combination of transverse and longitudinal motions.

Periodic Motion

Any motion that repeats itself at regular time intervals.

Period ($P$)

The time required for one cycle, calculated as $P = \frac{1}{\text{Frequency}}$.

Frequency

The number of complete cycles in a given time, measured in cycles per second or Hertz ($Hz$).

Hertz ($Hz$)

The unit of measure for frequency, equivalent to $1/s$.

Wavelength ($\lambda$)

The distance between a point on one wave and the same point on the next cycle of the wave.

Amplitude

The maximum displacement of the medium from its rest position; it is directly related to the energy a wave carries.

Wave Speed Formula

$\text{speed} = \text{wavelength} \times \text{frequency}$ or $\text{v} = \lambda \times f$.

Reflection

Occurs when a wave bounces off a surface that it cannot pass through.

Refraction

The bending of a wave as it enters a new medium at an angle because the two sides of the wave travel at different speeds.

Diffraction

The bending of a wave as it moves around an obstacle or passes through a narrow opening.

Interference

Constructive or destructive interaction that occurs when waves occupy the same region of space and then continue on.

Constructive Interference

Occurs when two or more waves combine to produce a wave with a larger displacement.

Destructive Interference

Occurs when two or more waves combine to produce a wave with a smaller displacement.

Standing Wave

A wave that appears to stay in one place; it forms only if half a wavelength or a multiple of half a wavelength fits exactly into the length of a vibrating cord.

Node

A point on a standing wave that has no displacement from the rest position due to complete destructive interference.

Antinode

A point on a standing wave where a crest or trough occurs, located midway between two nodes.

Sound Waves

Longitudinal waves consisting of compressions and rarefactions that travel through a medium.

Intensity

The rate at which a wave's energy flows through a given area, measured in decibels ($dB$).

Decibel ($dB$)

The unit that compares the intensity of different sounds based on powers of ten.

Loudness

A physical response to the intensity of sound, modified by factors such as age and the health of the ears.

Pitch

The frequency of a sound as perceived by the listener.

Infrasound

Sound at frequencies lower than what most people can hear, specifically under $20\,Hz$.

Ultrasound

Sound at frequencies higher than what most people can hear, specifically over $20,000\,Hz$.

Sonar

A technique for determining the distance to an object under water using reflection of sound waves; stands for sound navigation and ranging.

Doppler Effect

A change in sound frequency caused by the motion of the sound source, the motion of the listener, or both.

Outer Ear

The section of the ear that gathers and focuses sound into the middle ear.

Middle Ear

The section of the ear that receives and amplifies vibrations.

Inner Ear

The section of the ear that uses nerve endings to sense vibrations and send signals to the brain.

Resonance

The response of a standing wave to another wave of the same frequency, which can produce a dramatic increase in amplitude.