The process of change of physical quantities such as displacements, velocities, accelerations, and forces may be grouped into two categories; oscillatory and nonoscillatory. The oscillatory process is characterized by alternate increases or decreases of a physical quantity. A nonoscillatory process does not have this feature. The study of oscillatory motion has a long history, extending back to more than four centuries ago. Such a study of oscillatory motion may be said to have started in 1584 with the work of Galileo (1564–1642) who examined the oscillations of a simple pendulum. Galileo was the first to discover the relationship between the frequency of the simple pendulum and its length. At the age of 26, Galileo discovered the law of falling bodies and wrote the first treatise on modern dynamics. In 1636 he disclosed the idea of the pendulum clock which was later constructed by Huygens in 1656.
- Ogata K (2004) System dynamics, 4th edn. Pearson/Prentice Hall, Upper Saddle RiverGoogle Scholar