Objective
Using a simulation, apply the scientific method to investigate the various properties of
transverse waves.
1. Go to the “Wave on a String” simulation on the PhET simulations website at
http://phet.colorado.edu/en/simulation/wave-on-a-string. Click the play arrow on the
simulation graphic to run the web-based simulation or click DOWNLOAD to run the
simulation locally on your device.
2. Get oriented to the simulation by exploring and manipulating all the possible variables and
options:
a. MODE: manual, oscillate, pulse. In Oscillate and Pulse modes, you can pause/play, step,
and also change other settings regarding the wave characteristics
i. Amplitude: 0 to 1.25 cm
ii. Frequency: 0 to 3.00 Hz
iii. Damping: None to Lots
iv. Tension: Low to High
b. END: fixed end, loose end, or no end
c. Rulers: Display (box checked) or not (box unchecked). When displayed, you will see two
rulers: one horizontal and one vertical.
d. Timer: display (box checked) or not (box unchecked); start/pause/reset
e. Reference line: dashed line that can be used as a reference for amplitude
measurements
Note: The rulers, timer, and reference line can all be dragged around as needed. In addition
to the reference line, there is another dashed line parallel to the undisturbed string that is
fixed (not moveable).
f. Restart button: starts the simulation over for the current settings
g. Reset button (circular button with a circular arrow, on the lower right of the screen):
resets the simulation to the default settings
h. Pause button ( I I ): simulation is running when this is showing; press to pause the
simulation
i. Play arrow ( > ): simulation is paused when this is showing; press to run the simulation
While getting oriented with the simulation, think about how the different wave properties
discussed in Chapter 6 are being illustrated in the simulation, and how changing things in
the simulation affects the wave properties.
3. After spending some time experimenting with the simulation, follow the steps below to
conduct four experiments. Before beginning, be prepared to write down your
observations.
Experiments
Experiment 1: Manipulating a Wave on a String
In this experiment, you will investigate and observe the properties of waves by manipulating a
string attached to an energy source.
Before completing the experiment, write down a hypothesis, based on your current
understanding after reading the background information for the activity, that makes specific
predictions for how the string will react to changes to the energy source and to changes to the
end of the string.
1. Experiment setup: Click the Reset button. The Mode will be set to Manual. Set the
Damping to None.
2. Experiment procedure:
a. Set the End to No End. Wiggle the wrench up and down at varying speeds and over
various distance ranges. As the wrench is wiggled, a wave disturbance is created and the
string to moving up and down represents energy being propagated along the string.
Observe how the properties (wavelength, frequency, and speed) of the wave produced
changes with the different wiggle action. Write down your observations.
b. After wiggling for several seconds, let go of the wrench and observe what happens.
Write down your observations.
c. Click Restart. Change the End to Loose End. Wiggle the wrench as in part a. Observe the
differences in the properties of the waves produced with the Loose End compared to No
End. After wiggling for a bit, let go of the wrench and observe what happens. Write
down your observations.
d. Click Restart. Change the End to Fixed End. Wiggle the wrench as in part a. Observe the
differences in the properties of the waves produced with the Fixed End compared to No
End and the Loose End. After wiggling for a bit, let go of the wrench and observe what
happens. Write down your observations.
Answer the questions below to help you formulate some results and conclusions for this
experiment. You may need to do some additional experimentation to answer the questions.
1. In part a. of the experiment:
a. Based on the definitions of transverse and longitudinal waves (chapter 6), which
type of wave – transverse or longitudinal – is being generated along the string?
Explain how you determined this.
b. How is the wave frequency and wavelength affected when the wrench is wiggled
faster?
c. How is the wave amplitude affected when the wrench is wiggled farther up and
down?
2. For which end setting(s) is wave interference taking place? Explain what causes the
interference.
3. For which end setting(s) does the energy propagate away from the source without
returning? Explain why the energy does not return.
Experiment Results and Conclusions
Based on your observations while performing the experiment and your answers to the
questions above, formulate some results and conclusions for how the string will react to
changes to the energy source and changes to the end of the string.
Experiment 2: The Effects of Damping and Tension
In this experiment, you will investigate and observe the effects of adding tension or damping to
a wave.
Before completing the experiment, write down a hypothesis, based on your understanding
after reading the background information for the activity, that makes specific predictions for
how adding tension in the string, or damping the energy along the wave, will affect the
amplitude, wavelength, and speed of the wave being generated by the oscillator.
1. Experiment setup: Click the Reset button, and then click the pause button ( I I ) so that the
play arrow ( > ) is showing. Set Mode to Oscillate, set Damping to None, set Tension to
Low, set end to No End, and display the Rulers. You do not need to adjust the frequency
and amplitude settings. For this experiment, we will be changing the Damping and Tension
settings.
2. Experiment procedure:
a. Click the play arrow. After the oscillation wheel has turned several times, gradually
adjust the Damping from None to Lots. Observe how the amplitude, wavelength, and
speed of the energy propagating along the string all change as the damping is increased,
using the rulers as an aid in determining the relative changes (you do not need to take
any measurements). Write down your observations.
b. Repeat the setup in part 1 above.
c. Click the play button. After the oscillation wheel has turned several times, gradually
adjust the Tension from Low to High. Observe how the amplitude, wavelength, and
speed of the energy propagating along the string change as the tension is increased,
using the rulers as an aid in determining the relative changes (you do not need to take
any measurements). Write down your observations.
Experiment Results and Conclusions
Based on your observations while performing the experiment, formulate some results and
conclusions for how the independent changes made to the damping and tension each
affect the amplitude, wavelength, and speed of the wave being generated by the oscillator.
Experiment 3: Measuring Wavelength
In this experiment, you will measure the wavelength of a wave produced along the string for
different settings of the wave frequency.
Before completing the experiment, write down a hypothesis, based on your understanding
after reading the background information for the activity, that makes a specific prediction for
how changing the wave frequency will affect the wavelength.
1. Experiment setup: Click the Reset button. Set Mode to Oscillate, set Amplitude to 0.50 cm,
set Frequency to 1.00 Hz, set Damping to None, set the Tension to high, set the End to No
End, and display the Rulers. For this experiment, we will be changing the Frequency setting.
2. Experiment procedure:
Construct a table like the one below. Complete the following steps to complete the table.
a. After observing the generated waves with the oscillation wheel turning, click the pause
button.
b. Measure the wavelength in centimeters (cm), by using the horizontal ruler to measure
the horizontal distance between consecutive wave crests (highest part of the wave) or
between consecutive wave troughs (lowest part of the wave). Write down the
wavelength value for this frequency setting in the table.
c. Change the Frequency to 2.00 Hz. Repeat steps a and b.
d. Change the Frequency to 3.00 Hz. Repeat steps a and b.
Frequency
Setting
Measured
Wavelength in
Centimeters (cm)
1.00 Hz
2.00 Hz
3.00 Hz
To check that you performed the experiment correctly, and to validate the correctness of
your hypothesis: Multiply the frequency (in Hz = 1/s) by the corresponding wavelength (in
cm). Recall from chapter 6 that: Wave speed (in cm/s) = Wavelength (in cm) X Frequency
(in Hz = 1/s). You should calculate the same speed, about 6 cm/s, for each of the frequency
settings.
Experiment Results and Conclusions
Explain how the data you collected in the experiment validates the relationship between
wavelength and frequency for waves traveling at the same speed, as described in Chapter 6.
If your data did not validate the relationship, go back and check that you performed the
experiment correctly.
Experiment 4: Calculating Wave Period
In this experiment, you will investigate the relationship between wave frequency and wave
period, by counting the number of waves passing a given point for a given time interval and
performing a calculation.
Before completing the experiment, write down a hypothesis, based on your understanding
after reading the background information for the activity, that makes specific predictions for
how the period of a wave correlates to its frequency.
1. Experiment setup: Click the Reset button. Set Mode to Oscillate, set Amplitude to 1.00 cm,
set Frequency to 1.00 Hz., set Damping to None, leave the Tension on High, set the END to
No End, and display both the RULERS and TIMER. For this exercise, we will be changing the
Frequency setting.
2. Experiment procedure:
Construct a table like the one below. Perform the following steps to complete the table.
a. With the simulation running, position the timer above the 3 cm mark on the horizontal
ruler. You will be using the 3 cm mark as a reference point for counting waves passing it.
With the ruler and timer in these positions, you should be able to count wave crests
passing the 3 cm mark and also see the timer. Practice counting wave crests that pass
the 3 cm mark as the simulation runs. With each wave crest that passes, one cycle of the
wave has passed.
b. Start the timer and count the number of wave crests that pass the 3 cm mark in 10
seconds. Exact timing is not critical; just stop counting waves when the timer reaches
about 10 seconds.
c. Repeat step b, resetting the timer after each repeat, until you are confident that you are
counting the correct number of wave crests passing in 10 seconds. Record this value in
the designated location in the table.
d. Change the Frequency to 2.00 Hz. Repeat steps b and c.
e. For each frequency setting, divide the time interval (10 seconds) by the number of wave
cycles passing in 10 seconds. This calculates the amount of time in seconds that is
required for each wave to pass a given point, which is defined as the wave period.
Record each calculated period in its designated location in the table.
To check that you performed the experiment correctly, and to validate the correctness of
your hypothesis: In chapter 6, you learned that the wave period is equal to 1/frequency. So,
the inverse of the corresponding frequency setting (1/frequency) and the calculated period
should be very close in value.
Frequency
Setting
Time
Interval
Number of Crests
(Wave Cycles) Passing
in 10 Seconds
Wave Period
(10 seconds/number of wave cycles passing in 10 seconds)
1.00 Hz 10 seconds
2.00 Hz 10 seconds
Experiment Results and Conclusions
Explain how the data you collected and calculations you performed in the experiment
validates the relationship between wave period and wave frequency as described in
Chapter 6. If your data and calculations did not validate the relationship, go back and check
that you performed the experiment correctly.
Activity Submission
1. Create a document containing a report for each experiment. Your document should contain
four paragraphs, one for each experiment.
a. Title each paragraph with the corresponding name for each experiment, as it is stated in
the headings for the experiments above (e.g., Experiment 1: Manipulating a Wave on a
String).
b. For each experiment report:
i. Clearly and succinctly present your hypothesis for the experiment.
ii. Based on the information prompted for in the experiment’s Procedure and Results
and Conclusions section, clearly and succinctly summarize your observations,
results, and conclusions for the experiment, and include any data collected and
calculations made.
iii. Clearly and succinctly evaluate the correctness of your hypothesis based on the
information presented in part ii above.
