“If a tree falls in a forest and there is no one there to hear it, does it produce a sound?”
NAMES:
UNIT:
Waves and Sound
TITLE OF LESSON : The Nature of Sound as a Wave
BIG IDEAS:
MATERIALS:
Mechanical waves have specific characteristics and Sets of tuning forks, graduated cylinders, metal
predictable properties. Sound is an example.
and plastic rulers, wine glasses
MINISTRY EXPECTATIONS:
E2.4 investigate the relationship between the wavelength,
frequency, and speed of a wave, and solve related problems
[PR, AI]
One bell jar, one oscilloscope, one sound
generator
E2.1 use appropriate terminology related to mechanical
waves and sound, including, but not limited to: longitudinal
wave, transverse wave, frequency, period, cycle, amplitude,
phase, wavelength, velocity…
E3.6 explain selected natural phenomena …organisms that
..receive infrasonic, audible, or ultrasonic sound) with
reference to the characteristics and properties
STUDENT LEARNING GOALS:
* understand why sound is considered a wave
* produce and examine some sounds
* understand and use ways to model sound
* appreciate hearing in other animals and the
limits of sound and hearing
PRIOR KNOWLEDGE:
definitions and examples for key terms such as
medium, frequency, transverse and longitudinal
waves, crest, trough, wavelength, amplitude,
cycle, period – mounted in WORD WALL
use of slinky as model for sound
T/L STRATEGIES
A
1) Demo with Bell Jar
MINDS ON As air is pumped out the ringing bell
(15-20
becomes quieter until it cannot be
minutes)
heard
2) Refer to WORD WALL with terms
noted in PK above
APPENDICES
B 1) Sound Sources Instruction Sheet
B 2) Chalkboard notes
B 3) Student handout sheet
B 4) Notes for teacher on use of oscilloscope
C 1) Chart of hearing range of various Animals
C 2) Constant Loudness Curves
RATIONALE
Start thinking about
what sound is (needs a
medium)
Focus both sight and
hearing
Remind all students
about sound terms and
get them in the habit of
using them correctly
Self check
Link to previous day
ASSESSMENT
POE
TPS for the Explanation
Ask pairs of students for
meaning and examples
B
ACTION
(20-25
minutes)
(15-20
minutes
(15-20
minutes
C
CONSOLIDATION &
CONNECTION
(5-10
minutes)
NEXT
STEPS
1) Sound Sources Carousel
Students move through 4 stations
(two of each) to see how sounds can
be made and explored using a ruler,
a tuning fork, a wine glass and a
graduated cylinder with water
Appendix B 1)
See the similarities and
difference among 4
different sound sources
Control variable to
explore qualities of
sound (WW)
Each group reports to
whole class about one
thing they learned on
source assigned by
teacher
2) Notes on compression and
rarefaction, use WORD WALL where
appropriate
Link to tuning fork, speakers, drums
Appendix B 2)
3) Oscilloscope Exercises
Monitor sounds produced above.
Introduce hertz
Test hearing of class as frequency is
increased
Test hearing of class as loudness is
varied
Introduce decibel
Appendix B 3)
1) Comparing the hearing range of
different animals
Appendix C 1)
2) Examining the Constant
Loudness Curves
Appendix c 2)
To “draw” sound waves
using this model
To add to WW
Questioning during
note-making
A way to “see” sound
and have personal
experience with hearing
limits
To add to WW
Questioning during
note-making
Extend thinking to
analysis and application
Read handouts and
answer questions for
homework
Speed of sound
B 1)
Sound Sources Instruction Sheet
Musical Rulers
Tuning Fork Sounds
Position a ruler so it hangs over a desk. Firmly
clamp it with one hand and pluck it with the other.
What do you observe?
Make a prediction about how to change the
sound. Test it. Observe. Explain.
Repeat the test but changing something else this
time.
Pick up a tuning fork and strike it with a mallet.
Sounds from a Graduated Cylinder
Notes from a Wine Glass
Take the 100 mL graduated cylinder and fill it
halfway with water. Blow across the top of the
cylinder to create a sound.
Take the wine glass and fill it halfway with water.
Lightly moisten a finger near the tip and run it
around the top of the glass until you create a
sound.
Make a prediction about how to change the
sound. Test it. Observe. Explain.
Test your explanation by a second test.
Observe. Explain.
Find a different tuning fork and repeat . Explain
any differences in the observations.
Make a prediction about how to change the sound.
Test it. Observe. Explain.
B 2) Chalkboard notes
SOUND WAVES
The Bell Jar demonstration showed us that sound cannot travel in a vacuum. It needs a
medium such as air to move from the source.
The Carousel Activity showed how vibrating objects such as rulers, tuning forks and glass can
produce sound. We saw that we can change the frequency and the loudness by manipulating
these sources.
The Slinky exercise showed us how a longitudinal wave moves.
To further understand the nature of sound we need to think about what is happening at the
molecular level and picture the air particles.
Comparing the Slinky Wave to a Sound Wave
In the Condensation section the air particles ( and coils) are close together and in the
Rarefaction section the air particles (and coils) are far apart. Both are examples of longitudinal
waves because the waves move in the same direction as the wavelength. The air particles do not
move.
Both are longitudinal Waves
How the Sound gets to your ear
B 3) Student Handout to follow along with chalkboard notes
SOUND WAVES
What was demonstrated in the following devices about how sound is generated?
The Bell Jar
The Carousel Activity(rulers, tuning forks, glass)
The Slinky exercise
What is happening at the molecular level?
Comparing the Slinky Wave to a Sound Wave
Describe what is happening in the Condensation section.
Describe what is happening in the Rarefaction section.
Both are
________________________________
B 4) Notes for teacher on use of oscilloscope
An oscilloscope is an instrument that displays electronic signals on a monitor. It can be used to
“view” sounds by using a microphone to first convert the sound to an electronic signal and
then amplifying that signal.
1) A tuning fork will give a nice clean wave while other sounds will give more complicated
visuals. Vary the input, including the human voice, so that students can see the effects
on frequency (pitch) and amplitude (loudness).
2) Use a sound generator along with the oscilloscope to vary the frequency of a signal and
test the limits of members of the class. (You will be surprised how limited your own
capacity is.)
APPENDIX C 1)
Hearing Frequency Ranges for Various Animals
The range of hearing in animals is very broad. Examine specific values to answer the following questions.
1) Choose two animals of very different sizes. Compare their hearing ranges. Suggest an explanation.
2) Choose two animals of similar sizes that have very different ranges. Can you suggest why this might
be?
3) Find an animal with a very large range and describe how this might be useful in its life.
cies
Approximate Range (Hz)
human
64-23,000
dog
67-45,000
cat
45-64,000
cow
23-35,000
horse
55-33,500
sheep
100-30,000
rabbit
360-42,000
rat
200-76,000
mouse
1,000-91,000
guinea pig
54-50,000
raccoon
100-40,000
chinchilla
90-22,800
bat
2,000-110,000
beluga whale
1,000-123,000
elephant
16-12,000
porpoise
75-150,000
bullfrog
100-3,000
owl
200-12,000
chicken
125-2,000
APENDIX C 2)
CONSTANT LOUDNESS CURVES
The human ear is not equally sensitive to all frequencies. In other words, sounds of different intensities may actually
be perceived as having the same intensity (loudness) because their frequencies are different. (If this were not the case, a chart
like the one below would have flat lines instead of the curves you see.)
But the chart below shows research results. Each line displays the sound intensity level required at each frequency
for the sound to be perceived as having the same loudness. The lowest line can be called the threshold of hearing. It shows
the loudness level at which sounds of different frequencies are barely audible (0 dB). For example, a 100 Hz sound requires a
loudness of 35 dB to be barely audible. A sound with a higher frequency such as 1000 Hz only requires a loudness of 0 dB to be
heard. The highest line represents all sounds perceived as equally loud as a 1000Hz sound with an intensity level of 120 dB.
1) Notice that the top few lines are flatter than those below. What does this say about the ear’s sensitivity to various
frequencies at these fairly loud levels?
2) Describe the ear’s ability to “hear” sounds of various frequencies, when the sounds are fairly quiet.
3) Take into account your answers above and think how this play out in the following situation.
You have been listening to your parent’s sound system and set the balance knobs while listening to loud music. You
hear one of them approaching and quickly turn the system off. Later they discover that the balance seems off while
they listen to much quieter music. How would they need to adjust the balance controls. Explain why.