An image of the ear with labels:
Some Key Vocabulary
Sound: disturbance (or vibration) that travels through a medium as a longitudinal wave. The speed of sound depends on the elasticity, density, and temperature of the medium the sound travels through.
Elasticity: the ability of a material to bounce back after being disturbed.
Reflection: process by which sound waves bounce off a surface.
Diffraction: change in direction of sound waves as they pass through an opening or around a barrier in their path.
Interference: when two or more waves arrive at the same time and interact with each other
- Constructive: when two waves combine and the resulting wave has an amplitude that is bigger than the amplitude of either of the original waves
- Deconstructive: when two waves interact at opposite times and the resulting wave has an amplitude that is smaller than the amplitude of either of the original waves
Density: the amount of matter or mass in a given volume.
Loudness: a person’s perception of a sound. Loudness depends on the amount of energy it takes to make the sound and the distance from the source of the sound.
Pitch: how high or low the sound is perceived to be; the pitch of a sound wave depends on the frequency of the sound wave.
Intensity: amount of energy a sound wave carries per second through a unit area.
Doppler Effect: the apparent change in frequency of a wave due to the motion of the source. Ex: changing pitch of a police car siren as it moves by you. When a sound source moves, the frequency of the waves changes because the motion of the source adds to the motion of the waves.
Music: set of notes that combine in patterns that are pleasing.
Acoustics: study of how sounds interact with each other and the environment.
Reverberation: echoes of a sound that are heard after the sound source stops producing sound waves.
Resonance: when the frequency of a sound matches the natural frequency of an object.
Outer ear: acts as a funnel to gather sound energy
- Pinna: external part of the ear, gathers sound waves and directs them into the ear canal
- Ear canal: hollow tube that carries sound waves from outside of the human ear to the eardrum
- Eardrum: small, tightly stretched, drum-like membrane that vibrates and amplifies the sound
Middle ear: composed of the hammer, anvil, and stirrup; amplifies and transmits sounds into the inner ear
- Eustachian tube: tube that connects the middle ear to the back of the nose; equalizes the pressure between the middle ear and the air outside
Inner ear: converts sound waves into signals that travel to the brain
- Cochlea: snail-shaped tube/ fluid-filled cavity that is lined with receptors (tiny hairs) that respond to sound by moving when vibrated and creating a nerve pulse
- Auditory nerve: carries nerve impulses to the brain
Infrasound: sound waves with frequencies below the human range of hearing (20 Hz)
Ultrasound: sound waves with frequencies above the human range of hearing (20,000 Hz)
Echo: a reflected sound wave
Sonar (sound navigation and ranging): system that uses reflected sound waves to detect and locate objects underwater
Echolocation: the use of reflected sound waves to determine distances or to locate objects.
Sonogram: device that uses reflected ultrasound waves to create a picture
Sound is a mechanical wave that results from the back and forth vibration of the particles of the medium through which the sound wave is moving. If a sound wave is moving from left to right through air, then particles of air will be displaced both rightward and leftward as the energy of the sound wave passes through it. The motion of the particles is parallel (and anti-parallel) to the direction of the energy transport. This is what characterizes sound waves in air as longitudinal waves.
Compressions and Rarefactions
A vibrating tuning fork is capable of creating such a longitudinal wave. As the tines of the fork vibrate back and forth, they push on neighbouring air particles. The forward motion of a tine pushes air molecules horizontally to the right and the backward retraction of the tine creates a low-pressure area allowing the air particles to move back to the left.
Because of the longitudinal motion of the air particles, there are regions in the air where the air particles are compressed together and other regions where the air particles are spread apart. These regions are known as compressionsand rarefactions respectively. The compressions are regions of high air pressure while the rarefactions are regions of low air pressure. The diagram below depicts a sound wave created by a tuning fork and propagated through the air in an open tube. The compressions and rarefactions are labeled.
The wavelength of a wave is merely the distance that a disturbance travels along the medium in one complete wave cycle. Since a wave repeats its pattern once every wave cycle, the wavelength is sometimes referred to as the length of the repeating patterns – the length of one complete wave. For a transverse wave, this length is commonly measured from one wave crest to the next adjacent wave crest or from one wave trough to the next adjacent wave trough. Since a longitudinal wave does not contain crests and troughs, its wavelength must be measured differently. A longitudinal wave consists of a repeating pattern of compressions and rarefactions. Thus, the wavelength is commonly measured as the distance from one compression to the next adjacent compression or the distance from one rarefaction to the next adjacent rarefaction.