Content Benchmark P.8.C.2
Students know vibrations (e.g., sounds, earthquakes) move at different speeds in different
materials, have different wavelengths, and set up wave-like disturbances that spread away from
the source uniformly. E/S
If a tree falls in the forest and no one is around to hear it does it make a sound? This is a
philosophy question that might be answered scientifically. A wave is a transmission of energy by a
series of vibrations. Many types of waves are disturbances that travel through a medium and
transport energy from one location to another without transporting matter. The material or
substance through which the wave energy is transported is called the medium. In turn, the medium
can be a solid, liquid, or gas, which is a collection of interacting particles.
To learn more about what a medium is, go to
http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/u10l1b.html.
Sound is a wave produced by vibrating objects and needs a medium through which to travel. To
help answer the question about the tree in the forest, one must think of sound as a longitudinal
wave. But first, the difference between transverse and longitudinal waves needs to examined.
Characteristics of waves, such as, wavelength, frequency, amplitude, and speed (velocity) will also
be explored. Then how waves transfer energy differently in different materials will be
investigated. Next one has to understand the relationship between velocity, wavelength, and
frequency. The causes and effects of the Doppler effect will be looked at as well.
Types of Waves
A mechanical wave may be longitudinal, transverse, or a combination of both. We classify the
wave type based on the path in which the medium vibrates in relation to the movement of the
wave’s energy. Mechanical waves need a medium in order to transfer their energy from one place
to another. This transmission of energy cannot happen in a vacuum (i.e., a place where no medium
exists) for mechanical waves. In a transverse wave the particles of the medium vibrate in paths
that are perpendicular to the direction of motion of the wave. The illustration shows the
disturbance is perpendicular to the direction of travel of the wave.
Figure 1. Transverse Wave
(From http://www.phys.ualberta.ca/~trpk/phys100/waves/waves.html)
Remember that transverse waves are always distinguished by particle motion being
perpendicular to wave motion.
For an animation of a transverse wave, go to
http://www.acoustics.salford.ac.uk/feschools/waves/wavetypes.htm - introd.
For additional information related to waves, visit
http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/wavestoc.html.
Another type of mechanical wave is a longitudinal (or compression) wave in which a disturbance
causes the particles of the material to vibrate in a direction parallel to the direction of motion of
the wave. The disturbance is often referred to as a pulse when the wave motion is a single
disturbance or of short duration. The illustration below shows, that for longitudinal waves, the
medium vibration is in the same direction as the motion of the wave.
Figure 2. Longitudinal Wave
(From http://www.phys.ualberta.ca/~trpk/phys100/waves/wave2.jpg)
Keep in mind that for longitudinal waves the disturbance is parallel to the direction of
travel of the wave. Sound waves are longitudinal waves. Sound waves happen when the
atmosphere is alternately compressed and stretched. The backward and forward motion of a
speaker or the clapping of your hands produces these sound waves. The P waves of an
earthquake are also an example of a longitudinal wave.
For an animation of a longitudinal wave, go to
http://www.acoustics.salford.ac.uk/feschools/waves/wavetypes2.htm.
The third type of mechanical wave is often referred to as a surface wave, which combines
properties of both transverse and longitudinal waves. Surface waves occur on Earth’s surface
when generated from an earthquake and surface waves are also seen traveling along the surface
of an ocean. With a surface wave, the particles of the medium travel in a circular motion
compared to the direction of energy transfer. Only the particles at the surface of the
medium experience the circular motion, which is shown in the illustration below.
Figure 3. Surface Wave
(From http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/u10l1c.html )
For a wave to be generated, there is a preliminary displacement of a molecule someplace in the
medium. Just as an earthquake has a focus, any wave traveling through a medium has a
source. The molecules, which are displaced from their equilibrium position always progress in
the same direction as the starting place of the vibration.
To learn more about ocean surface waves, go to
http://blackmagic.com/ses/surf/papers/wavephysics.pdf.
Properties of Waves
To better understand waves, we will now look at their properties, or in essence, dissect a wave.
First we will look at a transverse wave, and then, make a comparison to the longitudinal wave.
The image will show the parts of the wave.
Figure 4. Crest and Trough
(From http://www.howstuffworks.com/noise-canceling-headphone.htm)
In the figure of the transverse wave above, the line running through the center of the wave
corresponds to the rest position or equilibrium position of neutral molecule movement. The
crest is the point where the vibration has the most amount of positive displacement from the
rest position. Conversely, the trough is the point where the vibration has the greatest amount
of negative displacement. The maximum displacement of any molecule in the medium relative
to equilibrium is called the amplitude of the wave. When thinking about sound waves, the
“volume” of the sound is strongly linked to the sound waves’ amplitude.
For more information on amplitude, go to
http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/u10l2c.html.
Now to compare the transverse wave to the longitudinal waves look at the diagram below.
Figure 5. Compression and rarefaction in a longitudinal wave.
(From http://www.howstuffworks.com/noise-canceling-headphone.htm)
A longitudinal wave has compressions and rarefactions, which are analogous to the crests and
troughs of the transverse wave. A compression is the part of the longitudinal wave where the
molecules of the medium are pushed closer together (e.g., higher pressure, more dense). A
rarefaction is the part of a longitudinal wave where the molecules of the medium are spread
apart the most (e.g., lower pressure, less dense).
To learn more about longitudinal waves, go to
http://www.kettering.edu/~drussell/Demos/waves/wavemotion.html.
If we look at a single molecule in the medium, the time it takes for its motion to repeat itself is
called the period (T) of a wave and it is measured in seconds. The number of times the motion
repeats itself in a specific time interval is known as the frequency (f) of the wave. When
referring to sound, frequency is equivalent to pitch. In other words the frequency is the
number of cycles per second (cycles/second). Frequency is measured in Hertz (Hz), which is
equivalent to cycles per second. Frequency and period are inversely proportional to each other,
1
as represented by the equation T  .
f
More information about the relationship between pitch and frequency can be found at
http://www.harmony-central.com/articles/tips/pitch_vs_frequency/.
The wavelength (  ) is the distance the wave energy travels in the time it takes to complete one
cycle. A wavelength can be measured from crest to crest (compression to compression) or
trough to trough (rarefaction to rarefaction).

Figure 6. Representation of wavelength.
(From http://www.bom.gov.au/weather/radar/about/images/wavelength.gif)
For a wave, the speed is the distance traveled by a given point on the wave (such as a crest) in
distance
a given interval of time. Represented in equation form, speed 
. Wave speed
time
depends upon the properties of the medium through which the wave is moving. A change in the
properties of the medium will cause a change in the speed, or if the wave transfers from one
medium to another. The speed of a wave is also a ratio of wavelength to period, which in

wavelength
equation form is speed 
. This equation is known as the wave equation. It states
period
the mathematical relationship between the speed (v) of a wave and its wavelength (  ) and
frequency (f). Using the symbols v,  , and f, the equation can be rewritten as v  f . The




important thing to remember is that wave speed is dependent upon medium properties and
independent of wave properties.
Further detail about waves can be found in the HS TIPS Benchmark P.12.C.1
Behavior of Waves
When waves travel through a medium they can reach the end of that medium and come across
another medium or obstacle. There are several possible results of a wave encountering a
barrier, a boundary, or another medium. One outcome is that a wave may be diverted
(reflected) in the opposite direction. For example, a sound wave may come into contact with a
wall and bounce back so that you hear an echo, which is a type of reflection. Direction change
will occur with a reflected pulse, and also, the amplitude will be less than the amplitude of the
incident pulse because energy is not completely conserved within the pulse (i.e., some energy
is transferred to the reflecting barrier).
To learn more about the reflection of sound waves, go to
http://hyperphysics.phy-astr.gsu.edu/hbase/Sound/reflec.html.
As a wave encounters the barrier between two media, some of the energy will be reflected and
some will be transmitted from the old media into the new media. If the differences between the
media properties are small, most of the wave’s energy will be transmitted and very little will be
reflected. If the two media have very different properties then little energy will be transmitted
and most will be reflected. Finally, if the wave travels from a less dense to a denser medium
the reflected wave will be inverted.
Waves can also change direction when traveling from one medium through another and this is
called refraction. The speed and wavelength of a wave changes as it passes into a different
medium causing the path of the wave to bend or refract. With sound waves the more elastic
the medium the faster the wave travels. As a result sound waves travel faster through solids
than they do liquids, and faster in liquids than in gases. The speed of sound in air depends
on the properties of air specifically the temperature and the pressure. A sound wave will travel
faster in a less dense material than a more dense material within a single phase of matter.
Therefore sound travels faster in warm air than in cool air. The two figures below demonstrate
why sounds can be heard at farther distances at nighttime, a phenomenon entirely due to
refraction.
Figure 7. In the daytime the air near the Earth’s
surface is warmer than the air above
and sound waves are refracted upward.
(From http://www.hk-phy.org/iq/sound_night/sound_night_e.html)
Figure 8. At nighttime, the air near the Earth’s surface
is cooler than the air immediately above
and sound waves are refracted downward.
(From http://www.hk-phy.org/iq/sound_night/sound_night_e.html)
Diffraction denotes a change in the direction of a wave when passing through an opening or
around a barrier in its path. Water and sound waves can diffract around corners or openings.
With increasing wavelength the amount of diffraction increases and the opposite applies to
decreasing wavelengths.
Figure 9. This photo shows water wave diffraction near the northern
coast of Norway. Waves bend as the pass around islands and coast
promontories creating complex interference patterns.
(From http://www.compadre.org/informal/index.cfm?Issue=18)
More information about reflection, refraction, and diffraction can be found at
http://www.glenbrook.k12.il.us/gbssci/phys/Class/sound/u11l3d.html.
Doppler Effect
Everyone is familiar with the sound of a siren on a moving vehicle. As the vehicle draws near, the
apparent pitch of the siren is increased; as the vehicle passes and then moves away, the apparent
pitch is decreased. The Doppler effect is perceived when the starting place of the waves is moving
with respect to an observer. The Doppler effect is the apparent shift in pitch (frequency) of a
source of sound because of the relative motion between the source and the observer. Water waves,
sound waves, light waves, etc. can all exhibit the Doppler effect. We are most familiar with sound
and the picture below demonstrates the Doppler effect in a sound wave.
Figure 6. Doppler Effect
(From http://www.glenbrook.k12.il.us/gbssci/Phys/Class/waves/u10l3d.html )
For an applet of the Doppler effect, go to http://www.lon-capa.org/~mmp/applist/doppler/d.htm
For more information on the Doppler effect, go to
http://hyperphysics.phy-astr.gsu.edu/Hbase/Sound/dopp.html
Another resource for information on the Doppler effect and sonic booms can be found at
http://www.kettering.edu/~drussell/Demos/doppler/doppler.html
Content Benchmark P.8.C.2
Students know vibrations (e.g., sounds, earthquakes) move at different speeds in different
materials, have different wavelengths, and set up wave-like disturbances that spread away from
the source uniformly. E/S
Common misconceptions associated with this benchmark
1. Students have difficulty understanding the correct characteristics of sound waves.
Consider the following statements showing student confusion about sound waves (from:
http://www.eskimo.com/~billb/miscon/opphys.html).
Loudness and pitch of sounds are confused with each other.
You can see and hear a distant event at the same moment.
The more mass in a pendulum bob, the faster it swings.
Hitting an object harder changes its pitch.
In a telephone, actual sounds are carried through the wire rather than electrical pulses.
Human voice sounds are produced by a large number of vocal chords.
Sound moves faster in air than in solids (air is "thinner" and forms less of a barrier).
Sound moves between particles of matter (in empty space) rather than matter.
In wind instruments, the instrument itself vibrates not the internal air column.
As waves move, matter moves along with them.
The driver changes the pitch of whistles or sirens on moving vehicles as the vehicle passes.
The pitch of a tuning fork will change as it "slows down", (i.e. "runs" out of energy)
As suggested by Mary O’Leary, in the referenced article, a conceptual change model may be
the best way to address these misconceptions. Students confront their preconceptions, and
through the conceptual change processes, develop a scientifically accurate model of the
concept. Background information is given on sound and then several lesson plans are provided
for use with students. Students confront the preconceptions through the activities and from
there develop a more accurate idea of the concept. The lessons provided are geared to 4th grade
students but they can easily be adapted to older students. The lessons and activities are
described in great detail and are easy to follow.
For further information on this misconception and for strategies to address it, visit
http://www.eskimo.com/~billb/miscon/opphys.html
2. Students incorrectly believe that an object must vibrate only at its natural resonant
frequency.
Students believe that waves traveling through different media will change a sound’s frequency.
In her Master’s thesis, Katherine VerPlanck Menchen discusses these misconceptions and
curriculum she developed to help students address the effects on the frequency of a sound with
respect to resonance and propagation. The curriculum uses guided inquiry labs to explore
sound in a hands-on style. The results are analyzed and evaluated in the article.
To read this thesis, go to http://perlnet.umephy.maine.edu/research/MenchenMSTthesis.pdf.
3. In regard to the Doppler effect, students incorrectly believe that the pitch is constantly
changing as the object gets closer.
Perhaps this misconception springs from the common example that teachers use to discuss the
Doppler effect: a siren on a passing police car. In this case, the police car passes by an
individual, and in fact, does get closer to the person hearing the siren. But getting closer does
not mean the pitch of the siren changes. Actually, the volume gets louder as the police car gets
closer. The pitch does change when the relative direction of the police car with respect to the
hearing person does change. At the instant the siren is no longer approaching the individual,
but now is going away, is the instant the pitch changes.
The Physics Forum website has several discussions from teachers and their students. One
discussion describes how many times students still retain misconceptions despite instruction.
One teacher describes that some misconceptions are ingrained and are extremely difficult to
dispel. The forum also discusses misconceptions introduced by textbooks and analogies used
in the classroom.
To access the Physics Forum, go to http://www.physicsforums.com/showthread.php?t=200359.
For an interesting article, go to http://www.physicsforums.com/showthread.php?t=200359
Content Benchmark P.8.C.2
Students know vibrations (e.g., sounds, earthquakes) move at different speeds in different
materials, have different wavelengths, and set up wave-like disturbances that spread away from
the source uniformly. E/S
Sample Test Questions
Questions and Answers to come in separate file
Content Benchmark P.8.C.2
Students know vibrations (e.g., sounds, earthquakes) move at different speeds in different
materials, have different wavelengths, and set up wave-like disturbances that spread away from
the source uniformly. E/S
Answers to Sample Test Questions
Questions and Answers to come in separate file
Content Benchmark P.8.C.2
Students know vibrations (e.g., sounds, earthquakes) move at different speeds in different
materials, have different wavelengths, and set up wave-like disturbances that spread away from
the source uniformly. E/S
Intervention Strategies and Resources
The following is a list of intervention strategies and resources that will facilitate student
understanding of this benchmark.
1. Exploring With Sound
This site gives students directions for a simple experiment that describes how sonar works. A
maze is created inside a shoebox with blocks of wood. Using marbles a person figures out
where the blocks of wood are located by listening to the sound.
To access this activity go to
http://www.tryscience.org/experiments/experiments_begin.html?sound.
2. How Speakers and Radar Work
The How Stuff works website has some excellent discussions about common items that
demonstrate scientific principles about waves. For example, the site has a thorough description
of how speakers’ function is provided and numerous illustrations are included. The article
briefly explains the basics of sound and how the ear interprets sound.
To interesting discussion can be found at
http://www.howstuffworks.com/speaker1.htm/printable.
Also at the How Stuff Works website is a complete description on how radio detection and
ranging (radar works) and its uses are presented in this article. The piece goes on to explain
echo and Doppler shift. Many useful links are given at the end of the article.
The radar discussion is found at http://science.howstuffworks.com/radar.htm
3. What Do We Mean By Crackling?
This is an interesting interactive site that describes things that crackle, such as paper, Rice
Krispies™, earthquakes, and magnets. You actually listen to the crackling noise and then
simple demonstrations are supplied along with some complex experiments to try.
To access this activity, go to http://simscience.org/crackling/index.html.
4. Experiment With Sonar
Sonar is the use of sound waves similar to radar. NOVA, a science program on PBS, has
developed a great website that discusses sonar, including a wonderful animation illustrates how
sonar works showing what you would “see” on a lake bottom or sea. The NOVA site then
provides a brief explanation, with images, on the uses of sonar.
The link to the visualization can be accessed at
http://www.pbs.org/wgbh/nova/lochness/sonar.html
5. Exploratorium Activities about Waves and Sound
The Exploratorium Science Museum in San Francisco has several terrific activities for students
to learn about science. In one activity, directions are given to create a musical instrument called
a Bonko. The site provides a clear explanation on what is going on with sound in the activity
and how the instrument works. A cultural connection provides information on different
countries that use an instrument similar to the Bonko.
To access this activity go to http://www.exploratorium.edu/science_explorer/can.html
Also at the Exploratorium site is an activity which allows students to create an ‘Ear Guitar.”
Clear directions are provided at this site, along with an explanation about the instrument works
and the underlying principles of sound waves.
The Ear Guitar activity is found at
http://www.exploratorium.edu/science_explorer/ear_guitar.html
Another fantastic site by the Exploratorium showing the application of sound in music. The
site is interactive with demonstrations, movies, and interviews. Students will find the site
engaging and interesting with the ability to create music in some of the interactive modules.
The history and culture of some musical instruments is also explored.
To access this site, go to http://www.exploratorium.edu/music/exhibits/index.html
6. What Is Seismology and What Are Seismic Waves?
The Michigan Tech Department of Geology has developed a tutorial for students on seismic
waves. This site, called “UPSeis” provides a good overview for middle school students by
describing earthquakes and their associated wave properties in nice detail.
Go to the UPSEIS site by clicking on http://www.geo.mtu.edu/UPSeis/waves.html.
7. Oceans Alive! – Water On The Move – Wind and Waves
The Museum of Science has an excellent site using ocean waves as an example to demonstrate
the scientific principles of waves. There is a concise explanation of a wave’s characteristics.
If you investigate the web site further a good deal of information is given on oceans.
To access this site, go to http://www.mos.org/oceans/motion/wind.html
8. NOAA Ocean Explorer: Sound in the Sea
This site provides brief description of the characteristics of waves is provided then ocean
acoustics is explored in depth. There is a wonderful collection of sounds from the sea and you
can listen to various whale sounds, ship sounds, earthquakes, and volcanic tremors. The
technologies used for ocean acoustic monitoring are explained. Biographies are provided of all
the different scientists involved in the project. The monitoring of global oceans through
underwater acoustics is explored in depth.
To access this site, go to
http://www.oceanexplorer.noaa.gov/explorations/sound01/background/acoustics/acoustics.html
This web site contains a selection of audio files that were recorded underwater, related video
and animations, and other images of ocean sound. The site shows how sonar, echolocation,
and sound waves work.
To access this resource, go to http://www.oceanexplorer.noaa.gov/gallery/sound/sound.html
9. How Your Brain Understands What Your Ear Hears
The National Institutes of Health provide this curriculum supplement. The module has a
teacher’s guide with lesson plans and implementation support. There is interactive material for
students that is impressive and aids students in gaining a deeper understanding of sound and
how we hear. This web site is useful for both teachers and students.
To access this educational module, go to
http://science.education.nih.gov/supplements/nih3/hearing/default.htm