What is Sound?What is Sound?Vibrations cause soundsVibrations cause soundsA A vibrationvibration is any rapid back and forth movement is any rapid back and forth movement (known as a disturbance)(known as a disturbance)Sound waves form when a Sound waves form when a vibrating object collides vibrating object collides with particleswith particles, transferring energy to them, and , transferring energy to them, and continues to pass on energy to other particlescontinues to pass on energy to other particlesSoundSound is a disturbance that travels through a is a disturbance that travels through a medium as a Compressional wavemedium as a Compressional waveA A compressional wavecompressional wave is a wave in which the is a wave in which the particles of the medium move back and forth in the particles of the medium move back and forth in the direction of the wave motiondirection of the wave motionSound waves are also considered Sound waves are also considered mechanical mechanical waveswaves,, waves that need the waves that need the presence of particlespresence of particles to to pass on energypass on energyOther mechanical waves are Other mechanical waves are seismic wavesseismic waves and and ocean wavesocean waves

Parts of a Compressional Wave”Parts of a Compressional Wave”

These waves have 2 These waves have 2 regions:regions:

compressionscompressions – – dense regions dense regions where molecules where molecules push togetherpush together

rarefactionsrarefactions – – less dense less dense regions where regions where molecules spread molecules spread apartapart

Direction of Sound WavesDirection of Sound WavesLight can only travel in a Light can only travel in a straight line straight line Unlike light, sound can Unlike light, sound can travel in travel in more than onemore than one directiondirectionWith a tuning fork, the With a tuning fork, the compressions and compressions and rarefactions rarefactions spread spread outward from the sourceoutward from the source in in all directionsall directionsThis is like dropping a rock This is like dropping a rock in a pond, the waves travel in a pond, the waves travel outwardoutward

Interactions of Sound WavesInteractions of Sound WavesSound waves can be Sound waves can be absorbedabsorbed by certain by certain materials and can muffle a materials and can muffle a soundsound– Ex: Carpet, curtains, foamEx: Carpet, curtains, foam

Sound waves can also be Sound waves can also be reflectedreflected by hard, smooth by hard, smooth surfacessurfaces– Ex: bare walls, caves, Ex: bare walls, caves,

mountain topsmountain tops

A reflected sound wave is A reflected sound wave is called an called an echoecho

Sound waves may also meet Sound waves may also meet and interact with each other, and interact with each other, known as known as interferenceinterference

Sound waves can spread out after Sound waves can spread out after passing through a doorway, and can passing through a doorway, and can

diffractdiffract,, or or bend bend around a corneraround a cornerfgfgfgfg

Sound Needs a Medium to TravelSound Needs a Medium to TravelRecall that a Recall that a mediummedium is any is any material through which a wave material through which a wave travels (solid, liquid, gas)travels (solid, liquid, gas)Light can travel through space Light can travel through space where there is no mediumwhere there is no mediumSound, however, Sound, however, requires the requires the use of particles to collideuse of particles to collide to to pass on energypass on energyWithout the presence of Without the presence of particles, the sound cannot be particles, the sound cannot be heardheardThis is why astronauts bring This is why astronauts bring their own radios to outer spacetheir own radios to outer spaceRecall that outer space is a Recall that outer space is a vacuumvacuum, an empty space with , an empty space with no particles whatsoeverno particles whatsoever

Will this bell be heard when it rings?

Determining the Speed of SoundDetermining the Speed of Sound

A sound wave’s A sound wave’s speed depends speed depends onon the substance of the substance of the mediumthe medium and whether the medium is a and whether the medium is a solid, liquid, or gassolid, liquid, or gasSound travels more quickly Sound travels more quickly through solids and liquids through solids and liquids because the individual molecules because the individual molecules are closer together than those of a are closer together than those of a gasgasThe The greater the densitygreater the density of the of the medium, the medium, the fasterfaster the sound the sound wave can travelwave can travelRecall that Recall that densitydensity is the amount is the amount of matter within a particular space, of matter within a particular space, or how compact something isor how compact something is

Speed and TemperatureSpeed and Temperature

As a As a medium’s medium’s temperature increasestemperature increases, , its its molecules move molecules move fasterfaster, and cause more , and cause more collisionscollisionsThis means that a This means that a sound sound wave can travel faster wave can travel faster through higher through higher temperaturestemperaturesThis graph illustrates the This graph illustrates the change in speed of a change in speed of a sound as the sound as the temperature of dry air temperature of dry air increasesincreases

http://http://www.brainpop.comwww.brainpop.com/science/energy/sound//science/energy/sound/

Recall the arrangement of the Recall the arrangement of the particles for each phase of matter:particles for each phase of matter: