What is Sound? Vibrations cause sounds A vibration is any rapid back and forth movement (known as a disturbance) Sound waves form when a vibrating object collides with particles, transferring energy to them, and continues to pass on energy to other particles Sound is a disturbance that travels through a medium as a Compressional wave A compressional wave is a wave in which the particles of the medium move back and forth in the direction of the wave motion Sound waves are also considered mechanical waves, waves that need the presence of particles to pass on energy Other mechanical waves are seismic waves and ocean waves

Parts of a Compressional Wave” These waves have 2 regions: compressions – dense regions where molecules push together compressions – dense regions where molecules push together rarefactions – less dense regions where molecules spread apart rarefactions – less dense regions where molecules spread apart

Direction of Sound Waves Light can only travel in a straight line Unlike light, sound can travel in more than one direction With a tuning fork, the compressions and rarefactions spread outward from the source in all directions This is like dropping a rock in a pond, the waves travel outward

Interactions of Sound Waves Sound waves can be absorbed by certain materials and can muffle a sound –Ex: Carpet, curtains, foam Sound waves can also be reflected by hard, smooth surfaces –Ex: bare walls, caves, mountain tops A reflected sound wave is called an echo Sound waves may also meet and interact with each other, known as interference

Sound waves can spread out after passing through a doorway, and can diffract, or bend around a corner fgfg

Sound Needs a Medium to Travel Recall that a medium is any material through which a wave travels (solid, liquid, gas) Light can travel through space where there is no medium Sound, however, requires the use of particles to collide to pass on energy Without the presence of particles, the sound cannot be heard This is why astronauts bring their own radios to outer space Recall that outer space is a vacuum, an empty space with no particles whatsoever Will this bell be heard when it rings?

Determining the Speed of Sound A sound wave’s speed depends on the substance of the medium and whether the medium is a solid, liquid, or gas Sound travels more quickly through solids and liquids because the individual molecules are closer together than those of a gas The greater the density of the medium, the faster the sound wave can travel Recall that density is the amount of matter within a particular space, or how compact something is

Speed and Temperature As a medium’s temperature increases, its molecules move faster, and cause more collisions This means that a sound wave can travel faster through higher temperatures This graph illustrates the change in speed of a sound as the temperature of dry air increases

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