Peer Review

Moment of Inertia

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Effectiveness:

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Overview:: This is a simulation of a classic experiment for measuring moments of inertia. A mass is attached to a string wrapped around a turntable and released. The moment of inertia of the turntable and its contents can be found from the acceleration of the hanging mass. Several different point masses are provided; these can be placed at different positions on the platform. A hollow ring and hollow and solid spheres are also available. A selection of accelerating masses can be used.

This material has recently become for-fee. See comments below.
Type of Material:: Interactive simulation
Recommended Uses:: Online experiment or in-class demo.
Technical Requirements:: Needs shockwave plugin.
Identify Major Learning Goals:: To understand the relation between the moment of inertia and mass distribution and its impact on rotations.
Target Student Population:: Advanced high school physics students and introductory college physics students.
Prerequisite Knowledge or Skills:: Students should be familiar with torque and the methods of calculating the moments of inertia. Also, instructors should derive the basic equation describing the system, since this is not done in the associated documentation.

Rating:
Strengths:: This is a well-executed simulation of a classic experiment to measure moments of inertia. It effectively invokes real experimental apparatus.
Concerns:: The documentation is rather sketchy. In particular, the formula relating moment of inertia of the rotating system to the acceleration of the suspended mass is presented baldly, without explanation. Also, the applet displays the acceleration of the system to five significant figures at the end of the simulation, much higher precision than would be possible for a real experiment of this sort.

Rating:
Strengths:: This applet allows students to perform virtual experiments that probably will not be generally available to them as a physical lab. It has sufficient options for a variety of student assignments. Students are allowed to run the lab and investigate unknowns as they wish.
Concerns:: The acceleration of the hanging mass is simply given by the simulation. It would be better if students had to determine it in some fashion (e.g. by measuring the time it takes the mass to fall through a known distance). Thus, they are not required to conceptualize or create an operational picture of the experiment and the quantities involved.

The help for the simulation gives a formula that can be used to determine the moment of inertia from the acceleration. If allowed to see this, students will not have to understand or derive the results, leading to a "plug and chug" operation of the virtual experiment.

Rating:
Strengths:: The simulation is simple to operate. All operations are drag and drop, and behave very much like a real experiment.
Concerns:: The online help gives results with no physical explanation or derivation. The use of the three unknown objects is not clear.

Other Issues and Comments:: Access to this material has recently become by subscription. Although the MERLOT/Physics does not usually review for-fee materials, this review will remain available for our users.
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