Sound

As an object vibrates it gives off energy to the particles of matter around it. These vibrations travel through air in a series of rarefactions and compressions (a longitudinal wave) Sound is produced as the matter vibrates and travels as a longitudinal wave A medium is required for sound to be heard. If a tree falls in the forest and no one is around to hear it, is there a sound? How vibrations cause sound:

  The speed depends on the properties of the medium. Sound can travel through any medium (solid, liquid or gas).   Speed is determined by the temperature, elasticity and density of the medium through which the sound travels. Speed of Sound

1. 1. Temperature: Sound travels slower at low temperatures Elasticity (ability to rebound): The more elastic the medium the faster the sound. Solids are more elastic than liquids or gases Density: The more dense the medium the faster the sound travels, its particles do not move as fast The fastest sound needs high temperature and a solid medium to travel through. Properties

  Pitch: description of sound as high or low, depends on how fast the particles of the medium vibrate in a given time (the frequency) so… the pitch depends on the frequency of the waves. High frequency = high pitch Low frequency = low pitch   Doppler Effect: Change in pitch of   a moving object as it comes towards   and moves away from you.   (NASCAR, Siren) High pitch as they move toward you and low pitch as they move away from you. Pitch

  1 hertz = 1 wave (1 complete rarefaction and compression)   Humans hear from 20 to 20,000 hertz   Ultrasonic: frequencies higher than 20,000 hertz; examples: dogs, cats, porpoises, bats   Infrasonic: Frequencies lower than 20 hertz; examples: elephants, earthquakes, volcanoes, machinery   Echolocation: use of reflected sound waves to find objects, bats & dolphins use it! Frequency HIGH PITCH LOW PITCH

  Loudness is related to the amount of energy carried by a wave ** Amplitude shows loudness**   Intensity: determines the loudness of a sound. Defined as the amount of energy in a certain time, relates to amplitude   Amplitude: the larger the amplitude the greater the intensity (loudness)   Decibel: scale in which intensity is judged.   0 dB = no sound, thunder is 120 dB, sounds with a dB of greater than 120 can cause pain in humans, 85 dB can cause ear damage Loudness SONIC BOOM

Resonance when one object vibrates at the same natural frequency of a second object it can force that second object into vibrational motion… basically it starts making noise also. LOOK AT THE VIDEO CLIPS!!! Examples: 1. The ear when you distinguish different frequencies or tones in the sounds you hear. 2. the shattering of crystal glasses when exposed to a musical tone of the right pitch (its resonance frequency). Glass Shattering: Tacoma Narrows Bridge:

  Music: when sound has a pleasing quality, a definite identifiable pitch and a repeated timing called rhythm.   Noise: any sound that is a random mix of frequencies or pitches. Examples include chalk on the chalkboard, jackhammer, baby crying   Acoustics – the science of sound. Scientists in this area design “perfect” concert halls and auditoriums.   Each instrument has its own sound quality or timbre. Sound quality

Sound is used for more than just hearing: Sonar: when sound waves are sent in a straight line down until it reaches a barrier and is reflected back. Used for fishing, to find oil, mapping Ultrasonic Cleaning: waves are used to clean jewelry, electronic components, machine parts. Sound waves are sent through a liquid where it vibrates causing dirt to be knocked off the object Ultrasound: sound wave sent through body and an image is drawn showing body part, can also be used to treat cancer and is used in physical therapy for injured muscles Applications of sound