Model Physics Unit Using the Model Physics Unit Using the Virtual Molecular Dynamics Virtual Molecular Dynamics

LabLab

Jacalyn Crowe and Cathy Abbot

Simple Harmonic Motion and Simple Harmonic Motion and WavesWaves

This unit is comprised of a series of learning activities on Simple Harmonic Motion and Waves. Using the SMD program, we have enhanced our current unit to strengthen student understanding of two particular topics:

Damped Harmonic Oscillators Speed of Sound

Damped Harmonic OscillatorDamped Harmonic Oscillator

Using the SMD program, students collect accurate data on the amplitude of a damped spring-mass system – a task difficult to accomplish in a wet lab situation. This simulation provides a visual and conceptual link between simple harmonic oscillators and sound waves.

Simulation Set-upSimulation Set-up

A green gas is compressed beneath a heavy red piston. When the piston is unlocked, it will rise to some maximum height, and begin to oscillate in simple harmonic motion.

Data CollectionData Collection

As the harmonic oscillator loses energy, the amplitude decays exponentially.

Students collect amplitude verses time data for the first five peaks.

Data AnalysisData Analysis

Students enter data into an Excel spreadsheet, find the exponential function and print the best-fit curve.

Embedded questions in the lab handout assess student comprehension.

Speed of SoundSpeed of Sound

The SMD program allows students to vary the properties of the medium to determine the effect on the speed of sound in a gas.

In addition, the simulation allows students to observe the displacement and kinetic energy of a single particle in the medium.

Simulation BeginsSimulation Begins

As the piston falls, a compression wave forms beneath the piston. At the position shown, the piston is locked and the wave begins to propagate.

The color of a particle represents its relative kinetic energy.

Initial Location of Initial Location of Compression Wave Compression Wave

The histogram shows the compression wave’s initial location, just beneath the piston.

Simulation EndsSimulation Ends

Students observe the compression wave and the behavior of an individual gas particle as the wave propagates to the bottom of the container.

Final Location of Compression Final Location of Compression WaveWave

The histogram indicates the compression wave’s arrival at the bottom of the container.

Data Collection and AnalysisData Collection and Analysis

Students repeat the simulation, gathering data on wave speed while changing the mass of the particles and the temperature of the gas. Students then determine the quantitative relationship between temperature and velocity, as well as mass and velocity. They then generalize their results to other situations.