If two spring pendula are coupled together by an attached
mass (Fig. 3) and one of the two systems is set into
motion, the oscillation performed by that pendulum soon
also transfers over to the other pendulum. Provided that the
springs used possess the same stiffness—i.e., the same spring
constant—the first pendulum remains briefly motionless
after some time; its oscillation energy has been completely
transferred over to the second pendulum. From then on, the
energy shifts between the two pendula, which is why each of
the pendula makes a typical swing motion.
The oscillations of coupled pendula of this kind can easily
be recorded with the help of two smartphones, which once
again serve as mass for the pendulum (Fig. 3). A measurement
example for a coupled mass of 100 g is shown in Fig. 4.
When the acceleration values, and therefore the amplitudes,
of one pendulum reach a maximum, the accelerations of the
other pendulum correspond approximately to the acceleration
of gravity, which equals a state of rest. The energy transfer
happens even faster if the two pendula are more strongly
coupled together. By varying the coupled mass, this aspect
can be examined in a subsequent experiment.
There is a complication when analyzing the data because
the measurements of both smartphones cannot be started
completely synchronously. In this case, the following method
has proved successful: The person conducting the experiment
starts the measurements on both smartphones separately and
waits for the systems to reach a state of rest. Then he or she