- Home
- Canvas Guide
Partial Progress - Circles (browser only)
Sound - Changing Pitch
Objectives
To create instruments that make different pitches.
Resources
Lined paper | Glass bottles & water
Today's Lesson
Main Activity
Today you will be making your own wind instrument and using it to change the pitch of the sound.
Set up a number of identical glass bottles (4 to 6) and fill each one with a different level of water. Ask your child to gently blow across the top of the first bottle to make a whistle sound. Predict what the pitch of sounds will be as you blow across each of the bottles.
| [W15] Image4.png | [W15] Image3.jpg |
Then ask your child to draw the apparatus being used and to make a note of which water level results in the lowest and highest pitch. Are the sounds from blowing across each of the three bottles the same pitch?
Keep these bottles for next week’s lesson.
Watch the video and ask your student to explain why the amount of liquid in the bottle affects the pitch.
Use this information to help guide the research:
An empty bottle produces a lower pitch because there is lots of air in the bottle to vibrate. Adding water to the bottle decreases the amount of air space, which means there is less air to vibrate. With less air, the vibrations happen more quickly and produce a higher pitch.
Optional Challenge
Please watch the following video with your student. In the clip, you will notice that the more liquid a bottle holds, the lower the pitch of the sound produced. This is strange because we discovered earlier in the lesson that bottles holding more water produce higher-pitched sounds when we blow across them.
Can your student explain why this investigation appears to have produced very strange results? What is the difference between this investigation and the one we asked you to complete earlier in the lesson?
Teaching note: In the 'Glass Bottle Xylophone' experiment, the side of a glass is tapped with the spoon. This causes the glass and water molecules to vibrate. The more water in the bottle, the harder it is to move it, meaning that vibrations are slower and any sounds created are lower-pitched.
When we blow across the top of a bottle, however, it is the air molecules that vibrate and produce sound waves. When the air molecules have less room to move, they vibrate more quickly, producing sounds of a higher pitch.