Waves and Sound
Lesson Plans
Although most of the activities provided for the study of the topic of waves and sound
involve vibrating objects producing sound, other types of mechanical waves and wave
behaviors are included. For each activity or demonstration, ask students what is vibrating
to create the disturbance. It is also appropriate to discuss the differences between a pulse
and a continuous wave, and the differences in the methods of producing them. Have
students focus on the transmission of energy along the path of the wave in each example,
recognizing that the vibrating object remains centered at its rest position.
An alternative activity to illustrate to students the difference between a pulse and a wave
is to have a student in the back left corner stand up and then sit down quickly. This is
identified as a disturbance in a medium. The next student is asked to perform the same,
singular activity, etc. All students are asked to perform the up-down motion one after
another. Students may call this a wave, but strictly speaking, it represents a pulse
traveling through the medium.
To make the activity illustrate a wave, have the first student stand up, bend down to touch
her toes, stand up again and continue to repeat the motion. The next student does the
same, beginning to bend down just as the previous student is beginning to stand up, the
process continues as the motion passes on to the next student etc. A wave begins with a
continuous vibration whereas a pulse begins with a single motion. Have students discuss
whether “The Wave” demonstrated by spectators at sports events is a pulse or a wave.
Some common misconceptions students may have with respect to waves and sound are:
 All waves travel the same way.
 There must be a medium for wave propagation.
 Light and sound have the same wave nature.
 Wave speed and frequency are the same.
 Pitch is related to loudness.
 Large amplitude waves travel faster than small amplitude waves in the same
medium.
 Waves transport matter from one place to another.
 Changes in wave speeds produce the Doppler effect.
In the conceptual development activity Wave at Me students are guided through wave
characteristics of transverse and longitudinal waves, define crest, trough, compression,
and rarefaction and discuss amplitude, frequency, wavelength, and period. You may
wish to check for understanding by having students line up and demonstrate “people
waves” of both transverse and longitudinal varieties. Emphasize that in transverse waves,
the individual particles move perpendicular to the direction of propagation of the wave,
whereas in longitudinal waves, the individual particles move parallel to the direction of
propagation of the wave (but not the whole length of the wave’s path). The examples in
this lesson are all mechanical waves requiring a medium to transfer the energy from one
location to another.
Jan Mader and Mary Winn
The Standing Wave Demonstrator expands the concept of wavelength and constructive
and destructive interference. A wave from a fixed point reflects back 180o out of phase so
the incident wave and the reflected wave will have equal wavelength and amplitude. If
the incident wave and reflected wave are in phase, a standing wave will be formed.
Standing waves occur when waves traveling both directions through a medium interfere
to produce nodes at regions of destructive interference and antinodes (or loops) at regions
of constructive interference. This phenomenon occurs for all types of waves. As an
alternate method of standing wave production, attach a cord on the end of a variable
speed drill and hook the other end of the rope to the wall on a rotating clip. As you vary
the speed of the drill the number of standing waves will also change.
If a ripple tank is unavailable the transparencies in Interference Patterns illustrate the
crests and troughs of a wave train as it passes through a double slit or originate from two
point sources. The nodal and anti-nodal lines are clearly visible and can be used to
explain the interference of both mechanical waves of water and sound as well as the
interference patterns generated when electromagnetic waves (light) pass through double
slit.
Most students have heard the pitch of a horn or motor change as it passes them, a
common occurrence of the Doppler effect. Many have heard of “Doppler radar” used by
weather forecasters, but probably do not understand its operation or advantage over
regular radar. The Doppler Buzzer should give them a basic understanding of why the
detected frequencies change even though the emitted frequencies for a moving source
remain the same.
An excellent visual to illustrate the compression and rarefaction of wavefronts is the
following: Obtain at least three oval or circular hoops embroidery hoops of various radii.
Place them on the overhead projector concentrically and discuss these as wavefronts
produced by a stationary point source. Then place your finger in the center of the smallest
hoop and begin dragging it to one side, “bunching” the hoops in the direction of motion.
From previous study, we know that the wave speed is dependent solely on the medium,
so the “bunching up” of the waves in front of the detector (listener in the case of sound
waves) means that more wavefronts are reaching the detector in a given time, thus
producing a higher detected frequency. The opposite is true behind the moving source.
Since most students drive, your school resource officer may also be a tremendous source
of help with this concept if he/she will bring the RADAR and LASER detectors and
explain them to the class.
Additional activities for waves and sound may be found in the following AAPT PTRA
Manuals, which may be purchased from AAPT:
 Hobbs, Winn, and Senior, Role of Demonstrations in Teaching Physics, ©1999
AAPT
 Jodi and Roy McCullough, The Role of Toys in Teaching Physics, ©1995
AAPT
 Cox and Belloni, The Role of Physlets in Physics Education, ©2001 AAPT
 George Amann, Exploring Physics in the Classroom, ©2005 AAPT
 Amann and Callahan, Homemade Physics Equipment, ©2005 AAPT
 Clarence Baaken, et al, Teaching About Music, ©1998 AAPT
Jan Mader and Mary Winn