Sounds+Oh+justice

Sounds

__Sound in Air__ >> On a much smaller but more rapid scale, this is what happens when a tuning fork is struck, or when speakers produce music. __Media that Transmits Sound__ >> less intense, but severe noise can interfere with cellular processes in the organ and cause its eventual breakdown __Natural Frequency__ >> the Natural Frequency depends on the elasticity and the shape of the object >> it is also the frequency that requires the least amount of energy to continue this vibration __Forced Vibrations__ __Resonance__ __Interference__ __Beats__
 * All sounds originate in the vibrations of material objects
 * In a piano, a violin, or guitar, a sound wave is produced by vibrating strings.
 * In a saxophone, a vibrating reed.
 * In a flute, by fluttering column of air at the mouthpiece.
 * Your voice results from the vibration of your vocal chords
 * In each of these cases, the original vibration stimulates the vibration of something larger, or more massive- the sounding board of a stringed instrument, the air column within a reed or wind instrument, or the air in the throat and mouth of a singer.
 * This vibrating material then sends a disturbance through a surrounding medium, usually air, in the form of longitudinal waves.
 * Under ordinary conditions, frequency of the sound waves produced equals the frequency of the vibrating source.
 * We describe our impression about the frequency of a sound with the word __**Pitch**__.
 * Sounds waves with frequencies below 20 hertz are called __**Infrasonic.**__
 * Sound waves with frequencies above 20,000 hertz are called __**Ultrasonic.**__
 * We cannot hear infrasonic or ultrasonic sounds.
 * Dogs can ear frequencies of 40,000 hertz or more.
 * Bats can hear sounds at over 100,000 hertz.
 * Consider a long room with a door at one end and an open window with the curtains at the other end.
 * If you open the door quickly, you can imagine the door pushing the molecules next to it away from their positions, and into the neighboring molecules.
 * Those molecules push on their neighbors, and so on,...until you see the curtain flap out the window
 * A pulse of compressed air has moved from the door to the curtain.
 * This pulse of compressed air is called __**Compression**.__
 * When you close the door quickly, the door pushes the neighboring molecules out the door, leaving an area of low pressure behind the door.
 * The molecules in the room move towards the door to take up the space vacated by the molecules pushed out the door.
 * When the low pressure reaches the curtain, the flaps inward.
 * This pulse of low-pressure air is called __**Rarefaction**__.
 * For all wave motion, it is not the medium (air, water, rope, etc.) that travels across the distance, but a //**PULSE**// that travels.
 * In our example of the room, the pulse travels from the door to the window/curtain. We know this because both cases the curtain moves after the door is opened or closed.
 * If you swing the door open and closed in periodic fashion, you can set up a wave of periodic compressions and rarefactions that will make the curtain swing in and out of the window.
 * Sound travels in __**Solids**__, **__Liquids__**, and __**Gases**__.
 * While most sounds you hear are transmitted through the air, you can put your ear to the ground and hear sounds quicker than you can through the air.
 * Just as Native Americans did to hear the hoof beats of distant horses.
 * Solids and Liquids are generally good conductors of sound - much better than air.
 * In general, sound is transmitted faster in liquids than in gases, and still faster in solids.
 * Sound cannot travel in a vacuum, the transmission of sound requires a medium.
 * If there is nothing to compress and expand, there can be no sound.
 * if you have ever watched a distant person doing something like hammering, or chopping wood, etc. you should have noticed that the sound gets to you after you see the event.
 * This is also very evident when observing lightning and hearing thunder.
 * These kinds of experiences are evidence that sound is much slower than light.
 * **Rule**- the speed of sound in a gas depends on the temperature of the gas and the mass of the particles in the gas.
 * The speed of sound in dry air at 0c is about 330 meters per second or about 1200 km per hour or about one millionth the speed of light
 * Water vapor in the air and increases in temperature will speed up sound slightly
 * For every degree increase in temp above zero c, the speed increases by about 0.6 m/
 * The speed of sound in a solid material depends not on the materials density but on its elasticity (the ability of a material to change shape in response to an applied force then resume its initial shape once the force is gone)
 * Steel is very elastic putty is indelastic
 * Inelastic materials the atoms are relatively close together and respong quickly to each others motions transmiting energy with little loss.
 * Sound travels about 15 times faster in steel than in air and about 4 times faster in water than in air
 * **Loudness**- sound intensity is objective and is measured by instruments
 * Loudness is subjective and is a physiological sensation sensed in the brain
 * The unit for sound intensity is the decibel named after alexander graham bell inventor of the telephone.
 * the decibel scale for loudness is a logarithmic scale
 * the scale starts at 0, the threshold of hearing
 * at 10 decibels, we have normal breathing, 10 times as loud as 20 dB, a close whisper, 100 times louder than the bottom of the scale
 * at 40 dB, we have the sounds in a library, at 1,000 times louder than the threshold
 * at 60 dB is normal speech
 * at 70 dB is a busy traffic street
 * at 85 dB we have physiological hearing damage
 * at 90 dB we have an average factory
 * at 100 dB we have an old subway train
 * at 115 dB we have a loud concert
 * at 120 dB we have the threshold of pain
 * at 140 dB we have a jet engine, 30 meters away
 * While physiological hearing damage begins at 85 dB, the extent of damage depends on the length of exposure and on frequency characteristics
 * a single burst of sound can produce vibrations intense enough to tear the organ of Corti, the receptor organ in the inner ear
 * //Unfortunelty, the cells of the corti do not regenerate//
 * if you drop a wrench and a baseball bat on the floor, you hear very different sounds
 * when any object composed of an elastic material disturbed, it vibrates at its own special set of frequencies, which together form its special sound
 * an object's __**Natural Frequency**__ is the frequency at which an object vibrates when it is disturbed
 * a natural frequnecy is one at which minimum energy is required to produce forced vibrations
 * occur when an object is made to vibrate by another vibrating object that is nearby
 * sounding boards are not important part of all stringed musical instruments (non-amplified, aka - acoustic) because they are forced into vibration and produce the sound
 * A phenomenon that occurs when the frequency of a vibration forced on an object matches the object's natural frequency and a dramatic increase in amplitude occurs.
 * Means to re-sound, or sound again.
 * An example is pushing someone on a swing.
 * If you don't push at the right time (natural frequency), you don't get any addition to the swing.
 * If you push at just the right time, even small pushes will add to the amplitudes of the swing.
 * When you tune a radio set, you are adjusting the natural frequency of the electronics in the set to match one of the many incoming signals.
 * The radio then resonates to one station at a time, instead of playing all the stations at once.
 * Resonance occurs when successive impulses are applies to a vibrating object in rhythm with its natural frequency.
 * 1831
 * English infantry troops marching across a bridge inadvertently caused the bridge to collapse when they marched in rhythm with the bridge's natural frequency, since then it is customary for troops to "break step" when crossing bridges.
 * 1940
 * The Tacoma Narrows Bridge disaster is attributed to the wind (40 mph) producing a fluctuating force that resonated with the natural frequency of the bridge, steadily increasing the amplitude over several hours until the bridge collapsed.
 * Sound waves, like any wavs, can be made to interfere
 * When constructive interference occurs with sound waves, the listener hear a louder sound
 * When destructive interference occurs, the listener hear a fainter sound or no sound at all
 * Noisy devices such as jackhammers are being equipped with microphones and microchips that feed a mirror "image" of the sound made by the jackhammer to a pair of earphones worn by the person, canceling the sound
 * When two tones of slightly different frequency are sounded together, a regular fluctuation in the loudness of the combined sound is heard.
 * The sound is loud, then faint, then loud, then faint, and so on...
 * This periodic variation in the loudness of sound is called __**Beats**__
 * If you walk with someone who has a different stride, then there will be times when are both "in step" and other times when you are both "out of step"
 * If you have 2 tuning forks that are different frequencies and you sound them together, then there will be times when the interference in the waves will be destructive and other times when it is constructive
 * Beats can occur with any kind of wave
 * Beats are also a practical way to compare frequencies
 * Piano tuners listen for beats produced between a standard tuning fork and a particular string on the piano
 * When the frequencies are identical, the beats disappear
 * Orchestras tune the same way, listening for the beats to disappear