PURPOSE: To demonstrate the normal modes of a mechanical
system comprised of two discrete oscillators. Also, to show the beats of this
system.
DESCRIPTION: Two physical pendula are linked together by a weak spring.
Displace both pendula equally to one side and release them together in phase, as
shown in the photo at center. The is one normal mode of the system. It is the
slower mode. No beating will occur.
Start with both pendula displaced to opposite sides and release to move 180 degrees out of phase, as shown in the photo at right. This is the other mode for this system. It is the faster mode of oscillation and again no beat occur.
To show beats, start with one pendulum at rest in equilibrium and the other pendulum displaced from equilibrium, as shown in the photo at left. Energy will transfer back and forth between the two oscillators in a time interval of about four minutes. This is not a normal mode for the system.
EQUIPMENT: Coupled pendulums and spring as photographed.
SETUP NOTES: Stored in mechanics.
Updated by Jun Qi in 3/24/2000