Coupled Oscillators
So far we have considered simple harmonic oscillators such as a mass on a spring or a simple pendulum that have only one way of oscillating. These are characterised by a single natural frequency of oscillation. In this chapter we consider systems that consist of two (or more) oscillators that are coupled together in some way and that have more than one frequency of oscillation. We will see that this coupling produces new and important physical effects. Each of the frequencies relates to a different way in which the system can oscillate. These different ways are called normal modes and the associated frequencies are called normal frequencies. The normal modes of a system are characterised by the fact that all parts of the system oscillate with the same frequency. Coupled motion is important because oscillators rarely exist in complete isolation and real physical systems are usually capable of oscillating in many different ways. For example a noisy old car will have many coupled components that may be heard vibrating and rattling when the engine is running! At the microscopic level, vibrating atoms in a crystal provide an example of coupled oscillators. Coupled oscillators are also important because they pave the way to the understanding of waves in continuous media like taut strings. Wave motion depends on neighbouring vibrating systems that are coupled together and so can transmit their energy from one to another.