Sound

** Chapter 26: Sound **



 []  Review Questions: -What is the source of all sounds? -How does pitch relate to frequency? -What is the average frequency range of a young person's hearing? -Distinguish between //infrasonic// and //ultrasonic// sound -Distinguish between //compressions// and //rarefactions// of a sound wave. -How are //compressions// and //rarefactions// produced? -Light can travel through a vacuum, as is evidenced when you see the sun or the moon. Can sound travel through a vacuum also? Why or why not? -How fast does sound travel in dry air at room temperature? -How does air temperature affect the speed of sound? -How does the speed of sound in air compare with its speed in water and in steel? -Why does sound travel faster in solids and liquids than in gases? -How does loudness differ from different people? **Make sure you are able to answer all of these questions when finished reviewing this website**!

All sounds are produced by the vibrations of material objects. The source of all sound waves is vibrations.
 * Chapter 26.1-The Origin of Sound **

[] [] [] the sound wave in these instruments are produced by the vibrating strings.

vibrations in the saxophone are caused by a vibrated [] __ images/woodbrass/SAXOPHONE+TENOR+KEILWERTH+SX90R+MAT.jpg __ reed whereas the vibrations in a flute   [] are caused by a fluttering column of air at the mouthpiece. When you're singing your vocal cords are the ones doing the vibrating! Original vibrations stimulate the vibration of something larger or more massive. The frequency of the vibrating source, under normal conditions, equals the frequency of sound waves produced.

**Pitch**=refers to how high or low sound frequencies appear to be. A high pitched sound from a piccolo has a high vibration frequency, while a low pitched sound from a fog horn has a low vibration frequency.

As you grow older your hearing range shrinks, especially at the high-frequency end. we can't hear either sound waves.
 * Infrasonic**=sound waves with frequencies below 20 hertz
 * Ultrasonic**=frequencies above 20,000 hertz

** Chapter 26.2-Sound in Air **

**Compression**=a pulse of compressed air (or other matter); opposite of rarefaction [] [] [] When you open a door quickly, you can imagine the door pushing the molecules next to it away from their initial positions and into their neighbors. In turn, neighboring molecules push into their neighbors and so on, like a compression wave moving along a spring, until the curtain flaps out the window. Compression is the pulse of air that moved from the door to the curtain. Therefore, the arrow represents the compression air against the window curtain which should cause the curtain to fly away from the door and out the window.

**Rarefaction**=A disturbance in air (or matter) in which pressure is lowered. Opposite of compression

When you close a door quickly, the door pushes neighboring air molecules out of the room which produced an area of low pressure next to the door. Neighboring molecules then move into it, leaving a zone of lower pressure behind them (rarefied). Other molecules farther from the door, in turn, move into these regions which result in a pulse of rarefied air moving from the door to the curtain. The arrow represents rarefaction which causes the window curtain in return to fly toward the door.

Sound travels in many different places, usually you think in air but it can also travel and solids and liquids as well. [] Sound can be heard from the ringing bell when air is inside the jar, but not when air is removed. However, sound can't travel in a vacuum. The transmission of sound requires a medium. If there is nothing to compress and expand, there can be no sound. There may still be vibration, but without a medium there is no sound!
 * Chapter 26.3-Media That Transmit Sound **

** Chapter 26.4-Speed of Sound ** Have you ever noticed that you hear thunder //after// you see a flash of lightning? [] This proves as evidence that sound is much slower than light. The speed of sound in dry air at 0 degrees C is about 330 meters per second. Water vapor in the air increases this speed slightly. Increased temperature increases the speed as well. Elasticity also plays a major role in the speed of sound. The speed of sound in a material does not depend of the materials density. Elasticity is the ability of a material to change shape in response to an applied force, then resume initial shape once the force is removed. [] steel is very elastic while []  silly putty is inelastic. You would think it would be the opposite but elasticity isn't "stretchability". Some very still material are elastic! Sound travels about fifteen times faster in steel than in air, and about four times faster in water than in air.

** Chapter 26.5-Loudness ** The intensity of a sound is proportional to the square of the amplitude of a sound wave.



[]

An oscilloscope measures sound intensity. However, loudness is a completely different thing. It differes for different people. Loudness is subjective but is related to sound intensity. [] Alexander Graham Bell: the creator of the decibel (dB), and of course the telephone, thought this would measure sound intensity greatly! Starting with 0 at the threshold of hearing for a normal ear, an increase of each 10 dB means that sound intensity increases by a factor of 10. To read how each sound intensity unit is read, you add a 0 at the end of every 10 units. If you're comparing 0 to 10 then it would increase by 10 units. However, if you're comparing 20 db and 10 db, it doesn't mean 20 db is twice as intense but 10 times as intense as 10 db. Comparing 40 db and 60 db, 60 db is 100 times as intense.

[] If you want to figure it out this way your always welcome to!!

__ Answers to questions at top! __ -Vibrations of material objects -There are directly proportional -20-20,000 Hertz -Infrasonic are sound waves with frequencies below 20 hertz and ultrasonic are sounds with frequencies above 20,000 hertz. -Compression is a pulse of compressed air and a rarefaction is a disturbance in air (or matter) in which the pressure is lowered -Compressions are produced when molecules are pushed away from their initial and into their neighbors and so on. -A rarefaction is when neighboring molecules push away from each other to produce an area of low pressure, where neighboring molecules move into. -No because there is no medium through which the sounds can vibrate -340 m/s -With each degree in air temperature above 0 degrees C sped of sound increases of about .60 m/s. -Sound travels about 15 times faster in steel than in air, and about 4 times faster in water than in air -Because they are more elastic than air.
 * they are opposites!

Source: Hewitt, Paul G., __Conceptual Physics.__ Menlo Park, California: Addison Wesley Longman, Inc., 1999.