The Einstein model of solids considers each atom as a quantum mechanical version of one of these systems. They can be classified using a quantity given by 2 pi times the energy stored over the energy dissipated, also known as the Q factor. These systems may undergo damping, and the frequency of these objects is equal to the square root of the stiffness k over mass. Pendulums are an example of these systems at small amplitudes, and they can be described mathematically by setting Newton's Second Law equal to Hooke's Law. 
The Einstein model of solids considers each atom as a quantum mechanical version of one of these systems. They can be classified using a quantity given by 2 pi times the energy stored over the energy dissipated, also known as the Q factor. These systems may undergo damping, and the frequency of these objects is equal to the square root of the stiffness k over mass. Pendulums are an example of these systems at small amplitudes, and they can be described mathematically by setting Newton's Second Law equal to Hooke's Law. For 10 points, name these objects, exemplified by a mass on a spring.
The Einstein model of solids considers each atom as a quantum mechanical version of one of these systems.
Simple {Harmonic Oscillator}s [accept Simple {Harmonic Oscillation} or Simple{ Harmonic Motion} or {SHO} or {SHM}; prompt on partial answer]