We propose a very simple model of lattice dynamics of graphite and its intercalation compounds (GIC's): our model only uses five force constants for graphite, and seven for the GIC. It is used to calculate the dynamical matrix of the structure, and to obtain by matrix diagonalization the phonon vibration frequencies for each element of the first Brillouin zone. Making use of available experimental results concerning graphite as well as ${\mathrm{LiC}}_{6}$, we may approximate the parameters introduced in the model. Finally, with the results so obtained, we calculate a great number of physical properties of these compounds: specific heat, Debye temperature ${\mathrm{\ensuremath{\theta}}}_{\mathit{D}}$, bidimensional or tridimensional character, as well as elastic constants.