# A brief summary for chapter 6 of "Sound" by Jenny Karpelenia?

bandmanjoe | Middle School Teacher | (Level 2) Senior Educator

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Well, I'm not sure who Jenny Karpelenia is, but I can give you a quick synopsis (summary) of sound.

Sound is produced by vibrations.  A vibration is one quick back-and-forth motion of an object. Sound is one of two waves that travels as a longitudinal wave.  Longitudinal waves are like a slinky toy, where you have some of the coils all bunched up, and some of the coils pulled apart.  The bunched up parts are called compressions, while the pulled apart coils are called rarefactions.

Sound waves require a medium through which to travel.  A medium is a substance through which the wave may operate.  A great medium for sound is air.  If there were no air, we wouldn't be able to hear anything.  The speed of sound depends on the medium it is traveling through.  In air, sound travels at 343 m/s, while in water it travels at 1482 m/s.  Through wood, it travels at 3850 m/s.

How high or low a sound makes is called pitch.  Different frequencies (the number of sound waves passing per second) make up the different pitches.  Frequencies you can hear range between 20 Hertz and 20,000 Hertz.  Below 20 Hz is infrasonic, which means "below".  Above 20,000 Hz is called ultrasonic, ultra meaning "above".

Some technologies use sound wave principles.  The Doppler effect measures the apparent change in frequency produced by things that are moving.  Sonar is short for "sound navigation and ranging", used by ocean going vessels to see what kind of structures are beneath their ships.

Loudness is how soft or how loud a sound is perceived to be.  Amplitude is the measure of how far a wave is from it's resting position.  A larger amplitude means louder, a shorter amplitude means softer.  Loudness is measured in decibels.

Some well-known interactions of sound waves are echoes, which are reflections off hard surfaces; echolocation, used by bats to see their way in the dark; and ultrasonography, used to see inside a mother to check on the baby's progress.  Sound waves may interfere with each other; constructive interference is when two waves overlap each other and sound louder, while destructive interference is when a wave doesn't overlap properly and they cancel each other out.

Hope all this helps!  There is more in the reference I have attached.

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