Sound!!

Sound Waves Sound waves produced by a vibrating object are compressional (or longitudinal) waves. Sound waves can only travel through matter. The energy is transferred by collisions between the particles in the material. Faster thru solids, then liquids, then gases. -

Making Sound Waves Vibrations transfer energy to nearby air particles, producing sound waves in air. For example, when you talk, tissues in your throat vibrate to form sounds. -

Amplitude of a Compressional Wave The amplitude of a compressional wave depends on the density of compressions. Also depends on what it is traveling through. - Greater Amplitude Lesser Amplitude

Wavelength The wavelength of a compressional wave is the distance between two compressions or two rarefactions. - Wavelength

The Speed of Sound The speed of sound depends on the matter through which it travels. Through air, 771mph (at about 70oF.) Through water, 3,333 mph. Through iron, 11,475 mph. Through diamond, 26,840 mph! It will not travel at all through empty space (a vacuum). -

Sonic BOOM! As an object approaches the speed of sound, it can actually overtake the sound waves it creates. This causes a thunderous “boom” as the waves collide together and a shockwave is created. Happens often when jets fly “supersonic.”-

Sonic BOOM!

Sound and Temperature The speed of sound through a material increases as the temperature of the material increases. Ex: Sound travels through the air faster on a hot day versus a cold day. -

The Loudness of Sound What makes a sound loud or soft? The difference is the amount of energy. Loud sounds have more energy than soft sounds.-

Intensity The amount of energy that a wave carries is the intensity of the sound. -

Intensity The intensity of sound waves is related to the amplitude. High frequency or greater amplitude means a greater intensity. The further away you are from a sound, the lower the amplitude and frequency. -

Frequency and Pitch Pitch is the human perception of the frequency of sound. Sounds with low frequencies have low pitch and sounds with high frequencies have high pitch. -

Human Ear

Interference Two different sound waves moving in the same medium may interact with each other. Constructive Interference: The waves make one big wave. Destructive Interference: The waves cancel each other out. This is why auditoriums must be designed well or you get echoes or dead spots. -

Interference = + Constructive + = Destructive

Doppler Effect The effect created by the movement of a sound source. Ex: A police car with its siren on sounds different here versus here. -

Doppler Effect The source of sound always emits the same frequency. If the distance is large, then the waves will spread apart. If the distance is small, the waves must be compressed. -

Sound Waves – Source Not Moving

Doppler Effect – Source Moving

Doppler Effect– Source Faster than Sound

Doppler Effect– Source Much Faster than Sound

Reflection of Sound Echoes are sounds that reflect off surfaces. Repeated echoes are called reverberation. The reflection of sound can be used to locate or identify objects. -

Diffraction of Sound Diffraction is a bending of sound waves through an opening or around a barrier. Ex: sound in a classroom bends thru a door into the hall. -

Refraction of Sound Change of direction of sound waves thru a medium. Ex: Walls are solid then gas or insulation then solid again. Changes most thru different mediums. Most evident as sound travels over water. -