Harmonic oscillatory movement describes movement in which an object that has been displaced from its point of equilibrium is acted upon by a restoring force directly proportional to the amount of displacement. The classic model of such a movement is a weight attached to a spring, oscillating between the two extremes of maximum compression and maximum extension. In a simple (ideal) system as described, no energy is lost and the weight will oscillate for an infinite amount of time between the two extremes . Based on these principles, the position, velocity, and acceleration of such a weight can be modeled by sinusoidal equations, as demonstrated below .
Equations used to model simple harmonic oscillation in the case of a spring include:
- Restoring force: F = -k·x
k is the spring constant; x is the displacement from position of equilibrium; F is the restoring force 
- Position of the body: y = A·sin(ω·t + φ)
Y is position relative to the point of origin; A is maximum elongation; ω is angular frequency (given by ω=2·π·ƒ=(2·π)/T); T is the time to make one full oscillation; φ is the phase difference which gives the position of the body at T = 0 and its direction 
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- Proyecto Newton. MEC. SIMPLE HARMONIC MOVEMENT [online]. ©2012. [cit. 2012-12-10]. <Simple Harmonic Movement>.
- AMLER, Evžen. Acoustics [lecture for subject Biophysics, specialization General Medicine, The 2nd faculty of medicine Charles University in Prague]. Prague. 2012-11-12. .