## Friday, March 27, 2020

### Finishing Up Sound in Science Club

This was our third and final week on Sound.

In Waldorf, Physics is a sixth / seventh / eighth grade main lesson block topic. There are lots of good resources for these blocks; my favorite by far is Physics is Fun! A Sourcebook for Teachers by Roberto Trostli.

Friday, March 27

Prior to Meeting

During the Meeting

• review the results of student at-home activities
• encourage the children to make sketches and take notes; review that when designing an experiment you only change one variable at a time
• #9 - "The Pitch of Blown Sounds," page 45
from Physics is Fun! A Sourcebook for Teachers

a series of empty glass bottles of various sizes
• #10 - "The Pitch of Blown Sounds #2," page 46

a series of glass bottles of the same size, water, food coloring
experiment with shortening the air column
the taller the air column the deeper the sound
• #11 - "The Pitch of Plucked Sounds," page 46

dulcimer
the longer the string the deeper the sound
• #12 - "The Pitch of Percussive Sounds," page 47

xylophone, three bar chime
the longer the bar the deeper the sound

• #13 - "The Pitch of Percussive Sounds #2," page 48

drum, singing drum
the looser the drumhead the deeper the sound
(the amount of air inside a drum also influences its pitch)
• revisit the 256 Hz and 1024 Hz tuning forks from last week's lesson, explain Hz (one Hertz equals one vibration per second), explain that a higher frequency means more vibrations which means a higher pitch (the faster the eardrum vibrates, the higher the pitch you hear; the slower it vibrates, the lower the pitch you hear), look at the length of the tuning forks and compare with the length of the xylophone bars
• revisit "The Pitch of Percussive Sounds"

use bottles from demonstration #10 WITHOUT MOVING THEM

Trostli writes,

"A set of bottles or wine glasses with water can also be used. When students lightly strike the side of the bottle, they will note that the more water there is in the bottle, the lower the struck pitch. This is in sharp contrast to the principle of pitch production in blown sounds. In that demonstration, increasing the water in the bottle crated a shorter column of air and a correspondingly higher pitch.

"An interesting variation can be done by filling a series of equal-sized bottles with varying amounts of water to play a major scale. If one blows into the bottles, a scale can be heard. If the bottles are tapped, those that made the highest blown sounds (i.e., most water, least air) will have the lowest tapped sounds, and the scale will be heard in reverse."

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