Experiment: The Damping Effect Of The Pendulum

Experiment: The Damping Effect of Air Drag on a Pendulum Bruce Dillon Lane Matheson Carol Brunjes

Objective: To show students the damping effects that occurs due to air drag and heat loss.

Materials:  Simple Pendulum  Stop watch  Ring Stand  Graph paper  Cardboard protractor large enough to measure angles at the bottom of the pendulum  Tape

Procedures: 1. Set up pendulum and protractor as shown.

Pendulum

Table Top

Protractor

2. Measure the length of the top of the string to the center of the mass. Record in data table. 3. Pull the mass back to an angle of approximately 40 degrees. Record angle in data table. 4. Release the mass and measure the maximum angle every 15 seconds. Continue until angle is 5 degrees or less. Record angles in data table. Discussion: A simple pendulum produces simple harmonic motion when the displacement from the equilibrium position is small. The small angle is used to reduce the amount of drag due to the air. However, if the angle is large then drag needs to be considered. In this case the oscillations of the mass of the pendulum are subject to a drag force proportional to the velocity. The system is the said to be “damped”. In damped oscillations the amplitude decreases exponentially with time.

Questions for Students: 1. Graph your data with amplitude on the y-axis and time on the x-axis. 2. Does your data agree with theory? Explain your response. 3. At what value of t would you expect your pendulum to stop completely? 4. What are some errors that might skew your data? 5. As amplitude decreases, what happens to the periods?