- What happens to the sound quality as more water is added
to the bottle?
(The pitch goes up.)
- What happens to the amount of air within the bottle space
as water is added to the container?
(It decreases because the air is forced out of the bottle.)
- How does the mass of a vibrating object affect its pitch?
(The greater the mass, the lower the pitch.)
- Why does adding water to the bottle affect the pitch?
(As water is added, the pitch goes up because the size
of the vibrating air mass has decreased.)
2 - Tuned Whistles
- In what form was energy transferred from the master tone
maker to the other containers?
(The energy was transferred as sound waves that traveled
through the surrounding air.)
- Which container continues to ring after the empty master
(The empty test container.)
- Which container continues to ring after the 1/3-full container
(The 1/3-full container.)
- What relationship can you infer from these observations?
(Containers will vibrate "in-sync" if they contain the
same amount of water as the master tone maker.)
It All Together
Review how the cochlea separates sounds according to frequency.
Then, have students discuss the concept of a tuned "reed."
Apply this understanding to the transferring of whistle tones
between bottles. You might wish to present the following sequence
of scripted questions:
- What causes the central filament within the cochlea to
(Vibrations within the surrounding fluid.)
- How is the basilar membrane adapted to distinguish pitches?
(It has a series of fibers with varying lengths. Each
length responses to a specific frequency.)
- What caused the target container to produce the sound
of the master tone maker?
(Vibrations traveled through the air and struck the container
causing it to vibrate.)
- Why didn't all of the containers respond to the master
(Only the containers that were "tuned" to that frequency
- How is the tuning of the basilar membrane and the water-filled
(Objects or regions will vibrate if they are "in tune"
to the surrounding waves. If they are not in tune, they
When you gently tap on a glass with a metal utensil, you also
produce a musical note. Think about it. As you add water to
this glass, the sounded note drops in pitch. Can you explain
(In this case it is the container, not the volume of trapped
air that is vibrating. As water is added to the glass, it
becomes part of the "container." When a greater mass vibrates,
it produces a tone of lower pitch.)
activities in this guide were contributed by Michael DiSpezio,
a Massachusetts-based science writer and author of "Critical
Thinking Puzzles" and "Awesome Experiments in Light & Sound"
(Sterling Publishing Co., NY).
Academic Advisors for this Guide:
Corrine Lowen, Science Department, Wayland Public Schools,
Suzanne Panico, Science Teacher Mentor, Cambridge Public Schools,
Anne E. Jones, Science Department, Wayland Middle School,