In physics, a phonon is a quantized mode of vibration occurring in a rigid crystal lattice, such as the atomic lattice of a solid. The study of phonons is an important part of solid state physics, because phonons play a major role in many of the physical properties of solids, including a material's thermal and electrical conductivities. In particular, the properties of long-wavelength phonons give rise to sound in solids-hence the name phonon from the Greek f¿¿¿ (phone) = voice. In insulating solids, phonons are also the primary mechanism by which heat conduction takes place.