Peer Review

Rotational Dynamics Web Assignment

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Effectiveness:

Ease of Use:

Overview:: This is a Web assignment on the relationship between the moment-of-inertia of
a simulated Atwood machine with a twist -- the two masses are connected to
concentric pulleys with different radii. The assignment uses an embedded Java
applet written by Angel Franco Garcia.
Type of Material:: Assignment.
Recommended Uses:: This will be best used as a homework assignment or self-study designed to check
one's understanding of Newton's Laws for rotational motion. It should not be
used as an introduction to the material, but as an excercise after learning the
basics in other ways.
Technical Requirements:: Java enabled browser.
Identify Major Learning Goals:: The assignment will enable students to utilize the applet to make quantitative
and qualitative predictions regarding torques and their effects on a rotating
body. Successful completion will require the student to integrate their
knowledge of torques and relate it to angular acceleration and the
experimentally determined value of moment of intertia of an object.
Target Student Population:: High School or introductory college/university level physics. Calculus is not
required for the solution, but the problem is not easy.
Prerequisite Knowledge or Skills:: A basic understanding of Newton's Laws for rotations, how to calculate torques
and the relationship of angular to linear acceleration and how all these
concepts relate to each other.

Rating:
Strengths:: The assignment is clear and to the point. It utilizes an applet resource that
gets the physics right. This substantial assignment will definitely
benefit any student who is able to complete it. Both qualitative and
quantitative questions are provided.
Concerns:: The outer radius of the double pulley is not given, though it can be guessed
from the condition on the inner radius. The answer that is provided has no
units specified; in fact the answer is in kg-m², whereas the given or measured quantities are in cm and g. Although this is a problem with the
applet, the assignment should clearly warn students.

Rating:
Strengths:: Viewing the applet can clearly show students that the accelerations of the two
masses are different when the radii are different. The requirement to determine
the acceleration using the distance and time measurement is a nice touch. The
assignment can serve as an excellent check on a student's understanding of
the relevant physics for a typical rotational dynamic situation that is not a
simple single step plug-in type problem.
Concerns:: The first question, which is qualitative, could be improved by also asking the
students to observe the more usual case of equal radii, where the accelerations
are the same. The second question, which is also qualitative, would be a more
effective learning tool if some additional description were added to help guide
students to the key features, rather than just being a test of whether they
understand or not. The use of the phrase "In general" is not very informative.

Students need to be told what the units of the answer are.

Rating:
Strengths:: The assignment is reasonably well written and ties in appropriately with the
applet that it uses. The instructions are clear and use the applet resource in
a sound way.
Concerns:: The applet comes from a Spanish site and the controls are in Spanish. While the
most important controls are translated in the instructions for the user. It
would be helpful if the other control buttons were translated for the user.
(Perhaps a glossary should be provided.)

In particular, the radius edit box needs to be translated for the student, as it
figures prominately in the assignment.