This lecture covers the Debye solid, phonon frequencies, phonon dispersion, density of states, heat capacity of low-dimensional materials, thermal properties of free electron gas, inelastic neutron scattering, spectroscopies, phonon dispersion curves, Einstein solid, graphene vibrations, free electron gas kinetic energy, Fermi function, energy density, Thomas-Fermi density functional theory, Sommerfeld expansion, and heat capacity in metals.