Sound waves!

The Nature of Waves A wave is a repeating disturbance or movement that transfers energy through matter or space.

Waves… Just as the crest of a water wave is followed by a trough, the compression part of a sound wave is followed by an area where the particles are far apart.

The Physics of Sound

If a guitar string vibrates 5 times in 1 second, the frequency is 5 vibrations per second. One wave per second equals 1 hertz. The hertz is the measurement of frequency! Most people can hear frequencies between 20 and 20,000 hertz.

Pitch If something sounds very loud, it has a high pitch. A low pitch is more difficult to hear. The higher the frequency of a wave, the higher the pitch.

Pitch When you play a guitar, you can change the length of a string by pressing on it. This shortens the string and makes the frequency higher. This produces a higher pitch.

Do you remember: amplitude? The amplitude is the distance in a wave from the resting position to the top of the crest or to the bottom of the trough.

Loudness Another way to describe sound is by its loudness. If you strum a guitar string gently, the vibration is small, so the amplitude of the wave is small and the sound is _________. If you strum it with more force, the vibration has more energy. The amplitude of the wave is greater, and the sound is __________.

Decibels (dB) The loudness of sound is measured in units called decibels (dB). The unit refers to the intensity of the sound wave.

Decibels (dB) For every 10 decibel increase in loudness, the amplitude of the sound increases by a factor of 10 decibels. The sound of leaves rustling on a tree has a loudness of 10 decibels. A 20 decibel sound, such as a whisper, has an amplitude 10 times greater.

Homework Questions… 1.How is sound produced? (3 points) 2.If a bass has a frequency of 13 hertz, how many vibrations per second are there? (2 points) 3.What part of a guitar produces sound? (2 points) 4. Why are some sounds louder than others? (3 points) 5. In what units is the volume of sound measured? (2 points)

I think it’s time to quit boys and girls!