A transfer of energy through space or a medium without permanent movement of matter. Examples include water waves, sound waves, and light waves.
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Transverse wave
A wave where particles vibrate perpendicular to the direction of travel. Examples include light waves and water waves.
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Longitudinal wave
A wave where particles vibrate parallel to the direction of travel. Sound waves are the primary example of longitudinal waves.
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Amplitude
The height of a wave from its rest position; directly relates to the energy carried by the wave.
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Wavelength
The distance between two identical points on a wave, such as from crest to crest or trough to trough.
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Frequency
The number of complete waves produced per second, measured in Hertz (Hz).
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Period
The time taken for one complete wave to pass a point, calculated as Period = 1 / Frequency.
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Crest
The highest point of a transverse wave.
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Trough
The lowest point of a transverse wave.
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Sound production
Sound is produced by vibrations of objects that cause surrounding particles to move back and forth, transferring energy outward.
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Sound wave travel mechanism
Sound travels as a longitudinal wave through compressions (particles close together) and rarefactions (particles spread apart).
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Sound speed in different media
Sound travels fastest in solids (~5000 m/s in steel), slower in liquids (~1500 m/s in water), and slowest in gases (~340 m/s in air) because closer particles transfer vibrations more quickly.
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Loudness
The perceptual intensity of sound, determined by the amplitude of the sound wave; larger amplitude produces louder sound.
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Pitch
How high or low a sound is, determined by the frequency of vibration; high frequency produces high pitch and low frequency produces low pitch.
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Object size and frequency
Larger or longer objects vibrate more slowly with lower frequency, while smaller or shorter objects vibrate faster with higher frequency.
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Methods to change pitch in instruments
Pitch can be changed by altering length, tension, thickness of strings, or air column length in wind instruments.
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Sound reflection
The bouncing of sound waves off a surface, which occurs when sound encounters a barrier.
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Echo
A reflected sound heard separately from the original sound, occurring when sound reflects off distant surfaces at least ~17 m away, such as cliffs or mountains.
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Reverberation
Multiple overlapping reflections of sound occurring in enclosed spaces such as classrooms and concert halls.
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Good sound reflectors
Hard, smooth surfaces such as concrete walls that bounce sound waves effectively.
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Good sound absorbers
Soft, porous materials such as carpets and foam that trap and dampen sound waves.
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Sound dispersers
Rough or uneven surfaces that scatter sound in multiple directions instead of reflecting it in one direction.
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Ultrasound
High-frequency sound used in medical imaging because it reflects off body structures to create detailed images.
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Echo sounding (SONAR)
A technique using reflected sound waves to measure ocean depth or detect objects underwater.
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Acoustics
The study of sound and how it behaves in spaces, with applications in designing concert halls, soundproofing rooms, and reducing noise.
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Pinna
The outer visible part of the ear that collects sound waves and directs them inward.
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Ear canal
The passage that directs sound waves from the pinna to the eardrum.
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Eardrum
The membrane in the middle ear that vibrates in response to sound waves.
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Ossicles
Three small bones in the middle ear (hammer, anvil, and stirrup) that amplify vibrations from the eardrum.
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Cochlea
The part of the inner ear that converts vibrations into electrical signals for transmission to the brain.
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Auditory nerve
The nerve that carries electrical signals from the cochlea to the brain for sound interpretation.
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Human hearing range
The typical frequency range humans can hear is 20 Hz to 20,000 Hz (20 kHz).
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Infrasound
Sound frequencies below 20 Hz that are too low for typical human hearing.
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Ultrasound hearing
Sound frequencies above 20,000 Hz (20 kHz) that are too high for typical human hearing.
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Conduction deafness
Hearing loss caused by problems in the outer or middle ear such as earwax buildup or a damaged eardrum.
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Sensorineural deafness
Hearing loss caused by damage to the cochlea or auditory nerve, often resulting in permanent hearing loss.
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Short-term effects of environmental noise
Noise can cause distraction and reduced concentration in the short term.
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Long-term effects of environmental noise
Prolonged exposure to noise can cause hearing damage, stress, fatigue, and sleep disturbance.