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Peer Review

Doppler Effect and Shock Wave (Physics)

by Fu-Kwun Hwang


Overall Numeric Rating:

4 stars
Content Quality: 4 stars
Effectiveness: 4 stars
Ease of Use: 5 stars
Reviewed: Jul 18, 2003 by Physics
Overview: This applet qualitatively demonstrates the non-relativistic Doppler effect due
waves emitted from a moving point source, including the production of shock
waves. The usual parameters (wavelength, wave speed, source speed) can be varied within limits, and the user can measure the distance between wave crests to verify the Doppler formula. The simulation shows how the Doppler effect derives from the various motions involved.
Type of Material: Java applet
Recommended Uses: Lecture/Demo; Homework. The latter will require specific instructor designed
activities or assignments.
Technical Requirements: Browser with Java support.
Identify Major Learning Goals: To achieve qualitative and quantitative understanding of the Doppler effect.
Specifically a user will investigate relations between wave speed, source speed, initial wavelength and how this affect the distance between wave crests.
Target Student Population: Introductory physics in high school or college.
Prerequisite Knowledge or Skills: Algebra and study of waves (meaning of wavelength, frequency, wavespeed)

Evaluation and Observation

Content Quality

Rating: 4 stars
Strengths: The qualitative explanation for the change in wavelength is easily seen from the
simulation. The item gives a clear visual explanation of why the Doppler effect
occurs. The user is able to change several parameters to investigate a wide
range of conditions. Wave speed, wavelength, and source speed can be user
selected. The simulation can be stopped and restarted with a mouse click, and
time is displayed.
Concerns: While the simulation does an excellent job at presenting an overview, there is
no "observer" available in this simulation. The measurement tools allow
observations to be made from any point while the simulation is stopped, but the
physical presentation of an observer making measurements seems to finish off the
topic in the way it is often presented in most texts. This would at least
illustrate the two special cases considered in most classes and texts, moving
toward or away.

Potential Effectiveness as a Teaching Tool

Rating: 4 stars
Strengths: For a moving point source the simulation displays a topic that is usually
difficult to draw on a board in class. In addition to qualitative concepts, a
user will be able to make measurements and either derive or verify results of
the Doppler effect. The applet can also be used to clearly illustrate the
transition to shock waves.
Concerns: An instructor can use the applet as a lecture/demo to illustrate the qualitative
aspects of the Doppler effect. To use the item quantitatively as homework,
specific assignments will need to be created. In addition, for self study, the
students will need to be told that the circular lines represent (e.g.) spherical
wave crests since there is no discussion of the translation from the
simulation to an actual moving wave source.

The lack of units in the applet is troubling because it caters to the well-known
tendency for introductory students to ignore units.

Ease of Use for Both Students and Faculty

Rating: 5 stars
Strengths: Parameters can be easily changed, and the ability to toggle the motion on and
off makes measurement of the wavelength very simple. There are brief but clear instructions that descibe each control and action. Most of the use is self evident in the simulation.