3A70.27 • Coupled Oscillations: Normal Modes of Two Spring-Coupled Gliders

Location: Floor Demo

Photo shows the demonstration used at the University of Texas at Austin

Concepts Conveyed:

Simple harmonic systems of coupled oscillators have certain normal mode frequencies at which every oscillator in the system will oscillate when the system is oscillating in the corresponding normal mode.
While the system is oscillating in a normal mode, the oscillators may be in or out of phase and may have oscillations of different amplitudes.
Any way the system can oscillate is some linear combination of these normal modes.

Instructions/Notes:

Using the string-tied wooden blocks, displace the two free gliders in opposite directions, as far as the string allows.
Make sure the central marking on the string is aligned with the 80.0 cm mark (you can place a yellow flag here to remember) on the track.
Quickly remove both blocks from the track and observe.

Using the string-tied wooden blocks, pin the gliders against the tracks with the blocks, fully extending the string.
Displace the gliders the same desired amount (12-16 cm works best) in the same direction.
Quickly remove both blocks from against the gliders and observe.

Initiate the gliders in any other configuration and observe how their motion is a combination of the two.

Demo Staff

Clear the PASCO air track of any other demos and put them on the bottom shelf of the table.
Place one of the two gliders labeled “Fixed End” on the track with its inner, right, edge aligned with the 20.0 cm mark and the other with its inner, left, edge aligned with the 140.0 cm mark.
Clamp both of the “Fixed End” gliders to the track with the big C-clamps.
Place two of the “m—181g” gliders on the track between the two fixed gliders
Grab 3 of the springs and place each between any two gliders, threading the open ends of their handles through the top holes along the edges of the gliders.
Be sure to include the string-tied wood blocks labeled “Two Masses” with this experiment.
Reset the track as normal when putting up the demo.

Last updated on February 18, 2026