Peer Review

Loaded String Simulation

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Effectiveness:

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Overview:: This is a computer simulation of a vibrating string with fixed ends. It models
the string as a massless string connected a finite number of masses; the number
of these is under user control. Options to set the tension and damping are also
available. Motion can be initialized either by selecting individual modes, or
by plucking the string. A sound option is also available.
Type of Material:: Simulation
Recommended Uses:: Lecture demo and out of class assignments for vibrations and waves.
Technical Requirements:: Java Applet
Identify Major Learning Goals:: To understand the behavior of vibrating strings.
Target Student Population:: Lower and upper division undergraduate. Lower division students will need additional explainations from the instructor to make effective use of it, however.
Prerequisite Knowledge or Skills:: Students should have a basic knowledge of standing waves on strings.

Rating:
Strengths:: One of the best features of this applet is that it describes a loaded string rather than a continuous string. This makes possible comparisons between finite load scenarious and the continuous case. The string can be excited either by turning on various modes explicitly or by plucking it in a number of ways. There are also a number of ways to display the contribution of the various modes. The ability to hear the sound produced by the vibrating string is also a very nice touch.
Concerns:: Normally, in textbooks, we first understand vibrations of masses attached to springs (not strings); then learn about vibrations of strings separately. This simulation blends the two ideas, which may prove comfusing to some students. The author should provide some additional explanations to clarify the system

Rating:
Strengths:: The great strenghs here are the depth of the treatment and the excellent graphics. There are a number of alternative ways to view the contribution of the various modes to the overall motion.
Concerns:: The entire simulation is qualitative in nature, there is no way to obtain numerical values for any quantity within the simulation. Also, the drive force option is limited in its usefulness because its range is two limited. It would be nice to have the ability to excite resonances other than the fundamental.
Varying the tension did change the amplitude as advertised, but had little effect on the frequency. The option to vary simulation speed, although useful when trying to follow the motion of higher modes, is still out of step with the other controls, which all change physical parameters associated with the motion. An option to vary the mass, along with an effective tension control, could accomplish much the same thing.

Rating:
Strengths:: Although the purpose of some of the controls and displays used in the simulation are not always obvious, the directions that accompany the applet are clear and concise.
Concerns:: Instructors who wish to use this simulation for assignments will need to develop fairly detailed lesson plans for students if effective use is to be made of this item. The sound part does not work very well; there are a numerous clicks and pops. Also, the phase and amplitude controls are somewhat confusing. The amplitude controls can be used to set the amplitude, but the phase controls only show the current phase unless phasor mode is selected.

Other Issues and Comments:: An interesting applet that simulates how a string with beads on it would vibrate. The simulation would benefit a great deal if a detailed description of the underlying theory were attached.
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