This is a computer simulation of a common experiment on masses and springs in introductory physics labs. It can be used to perform standard experiments relating to Hooke's Law and Simple Harmonic Motion. It includes three springs, one of which has variable stiffness, a few standard masses, and some unknown masses. The value of g can also be varied. User-adjustable damping is included, although its nature is not specified. Also included are a ruler for measuring displacements and a stopwatch for timing motion.
To understand the Hooke's law and its applications in simple harmonic motion.
Target Student Population:
High school and lower division undergraduates.
Prerequisite Knowledge or Skills:
An introduction to concepts of force (although this simulation, if carefully scripted, could be used for such an introduction).
Type of Material:
In class demos, student assignments, or virtual labs and pre-labs.
Requires Macromedia's Flash Player plug-in.
Evaluation and Observation
Sufficient resources are provided to perform a number of different experiments. Students may find spring constants by using the known mass values and the dragable ruler to measure displacements. They can then use the results to determine the unknown masses. They can also perform experiments to investigate the relationship between period of oscillation and mass, spring constant, or amplitude. Graphs showing energy relationships are also available.
The damping control is labeled "friction", however the nature of the damping force is not discussed. If it is a velocity-dependent damping, it is probably a little misleading to call it friction. If it is something else, its nature should be explained, since friction resulting from contact between sliding surfaces normally would not be encountered with masses hanging vertically.
The energy graphs have some missing information. It is not clear where the reference level for gravitational potential energy has been located, but it appears to be out of the figure. The zero for elastic potential energy, likewise, does not seem to be quite at the height designated by a dashed line. Finally, the work done by the dissipative force is labeled "heat". Students should be made aware of this connection, and the definition of heat, as this is sometimes not treated at this point in a physics course.
The spring motion is constrained to the vertical direction, but there are no visual clues as to why.
Potential Effectiveness as a Teaching Tool
The ability to make quantitative measurements make this an excellent discovery applet. Easy to use tools are provided to make measurements of forces, displacements, and time. Force, energy, and harmonic motion can all be explored. The slider control that varies the spring constant for the third spring has no numbers; one end is labeled "soft",
the other, "hard". This is an effective way of conveying the physical effect of the control without giving away data about the spring that students can obtain for themselves by measurement.
Since the nature of the damping applied to the springs is unknown, the ability to change this is of limited utility.
The bar graphs for energy, while useful, might cause some confusion as indicated above. Students should be encouraged to consider the physics (or lack thereof) in the choice of the zero potential energy reference levels.
Ease of Use for Both Students and Faculty
All controls are obvious in their functions and seem to work flawlessly. The help screens are clear and concise in their explanations, which are provided in the form of balloons attached to the individual components. The graphics are excellent.
Occasionally, re-sizing the window may obscure parts of the applet window.
Other Issues and Comments:
This simulation is part of a growing collection created by the Physics Education Technology Group. These materials are designed based on research in physics education and studies of student usage of the simulations. Information about the results of research on the impact of the simulations and a database of instructor-submitted lesson plans are available on the web site.