Model Physics Unit Using the Virtual Molecular Dynamics Lab

1
Model Physics Unit Using the Virtual Molecular
Dynamics Lab

• Jacalyn Crowe and Cathy Abbot

2
Simple Harmonic Motion and Waves

• 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

3
Damped 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.

4
Simulation 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.

5
Data Collection

• As the harmonic oscillator loses energy, the
  amplitude decays exponentially.
• Students collect amplitude verses time data for
  the first five peaks.

6
Data 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.

7
Speed 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.

8
Simulation 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.

9
Initial Location of Compression Wave

• The histogram shows the compression waves
  initial location, just beneath the piston.

10
Simulation Ends

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

11
Final Location of Compression Wave

• The histogram indicates the compression waves
  arrival at the bottom of the container.

12
Data 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.