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# Peer Review

by Fu-Kwun Hwang

## Ratings

### Overall Rating:

Content Quality:
Effectiveness:
Ease of Use:
 Reviewed: Jun 27, 2001 by Physics Overview: This Java applet allows the user to qualitatively and quantitatively view one dimensional binary collisions in four different reference frames -- the lab frame, the center-of-mass frame, and the frames in which either of the two objects are at rest. Adjustable parameters include each speed, position, mass, and the elasticity of the collision. Learning Goals: To help students understand the meaning of different collisional reference frames, and what quantities are common among such frames. Target Student Population: Lower Level and Intermediate Undergraduate Prerequisite Knowledge or Skills: Basic 1D collisions and momentum conservation including concepts of velocity vector, frame of reference and center of mass. Type of Material: Lecture/Demo; Student Self-Study Technical Requirements: The velocity of the center-of-mass is not displayed in the lab frame, and the velocity of the right barrier is not displayed in any of the other frames while running under Netscape 4.75. Each is displayed under IE 5.5.

### Content Quality

Rating:
 Strengths: This is an excellent and useful applet for looking at collisions from different frames of reference. Very useful for exercises and for classroom lecture/demo. The ability to change on the fly to any of four different reference frames is a useful feature. Concerns: When the masses are very different from each other, and one starts moving very fast, it moves through the other one and through the walls. But then it still bounces back. The animation can be stopped with one object on the "wrong" side of the other object, which could then lead to some confusion. With a very high mass ratio, one will disappear for a while.One can sometimes change the velocity of m1 in the m1 rest frame by changing the CM velocity. (This is true only prior to starting the applet.)General Comments on Quality: Although the applet appearance is rather plain, it works well. The physics appears to be correct (e.g., momentum is conserved, energy is conserved when it should be), even in the limits. Calculations are done only to about 5 significant figures, so the velocity values can be off somewhat after many collisions. There are minor grammatical problems in the text, particularly in subject/verb agreement.

### Potential Effectiveness as a Teaching Tool

Rating:
 Strengths: Recommended Use(s) for Material: Lecture demo/Student exerciseThis is a great way to view a 1D collision from various frames of reference, a topic which is not easily described by text. Concerns: Use(s) Material is not Suited For: Tutorial (without additional text)At high mass ratio (or high speeds), the balls move through walls and each other. This is easily discounted with a word of caution, but even at low speeds, the walls will move off the page, allowing for a little bit of confusion. The lack of units reinforces bad habits of undergraduates, who tend to ignore units.General Comments on Effectiveness: Overall this applet has a good potential to be effective in teaching the concepts of collisions in different reference frames. Its effectiveness for self-study could be substantially enhanced by including assignments or suggested items for students to look at.

### Ease of Use for Both Students and Faculty

Rating:
 Strengths: A generally easy to use and straight-forward interface. The ability to pause/restart by toggling a mouse button is very useful. Concerns: The instructions describe a yellow arrow which is actually red. It is not immediately apparent to the uninitiated user what the blue numbers are indicating. Grammar in the instructions is problematic in places. It is difficult to click on-center to drag objects -- one often ends up changing velocity or mass instead. It is time-consuming to look at a case where one object is much more massive than another since the mass can be changed only by one unit for each click.General Comments on Usability: The applet is generally easy to use, and the display is for the most part self-explanatory, but is not entirely intuitive: the instructions need to read to gather the meanings and possibilities of adjusting parameters. You cannot change the mass by entering a number: instead you must click within the mass (as described in the instructions). Different mass objects are not visually apparent -- one must look at the parameter bar, which cannot be read at a glance.
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