Reflection on Properties of Sound

Sound Wave

          I thought that this chapter was very interesting.  We learned about intensity, loudness, frequency, pitch, and the Doppler effect.  Intensity is the amount of energy a sound wave carries - the more energy there is, the more the molecules of the medium move.  Intensity is measured in watts per meters squared.  Loudness is what you actually hear.  A sound wave of greater intensity sounds louder, whereas a sound wave with less intensity sounds softer.  Loudness is measured in decibels.  For every ten decibels, the amount of sound you have is ten times louder.  For example, 20 dB is 10 times as loud as 30 dB.  The textbook had some examples:  rustling leaves are 10 dB, a whisper is 20 dB, soft music is 30 dB, the average classroom is 35 dB, the average home is 40-50 dB, and a loud conversation is around 60-70 dB.  Frequency is the amount of vibrations per second a sound wave creates.  The higher the frequency, the higher the sound.  Sometimes, the frequency of a sound is either too high or too low for the human ear to detect it.  This is called either ultrasound (high) or infrasound (below).  Pitch is a description of how high or low a sound seems to a person.  It depends on the frequency of a sound wave, so the higher the frequency, the higher the pitch, and vice-versa.  When using a string instrument, the pitch depends on the length, tightness, thickness, and material of the string.  You can change the pitch by changing the properties of the string that produces it - you can tighten it and make it higher.  Lastly, the Doppler effect is what happens when you hear a siren from an ambulance or a police car go by.  When the car is behind you, the siren seems softer, when it's right in front of you, it seems loud, and when it has passed you, it seems quiet again.  This is because as the car approaches you, the sound waves come toward you more quickly, but once it's passed, the sound waves come to you more and more slowly, so they don't seem as loud to you anymore.

Doppler Effect