This is a more physically accurate approach, which uses the widely used finite element method to solve the partial differential equations which govern the dynamics of an elastic material. The body is modeled as a three-dimensional elastic continuum by breaking it into a large number of solid elements which fit together, and solving for the stresses and strains in each element using a model of the material. The elements are typically tetrahedral, the nodes being the vertices of the tetrahedra (relatively simple methods exist to tetrahedralize a three dimensional region bounded by a polygon mesh into tetrahedra, similarly to how a two-dimensional polygon may be triangulated into triangles). The strain (which measures the local deformation of the points of the material from their rest state) is quantified by the strain tensor ϵ ϵ . The stress (which measures the local forces per-unit area in all directions acting on the material) is quantified by the Cauchy stress tensor σ σ . Given the current local strain, the local stress can be computed via the generalized form of Hooke's law : σ σ = C ε ε where C is the elasticity tensor, which encodes the material properties (parametrized in linear elasticity for an isotropic material by the Poisson ratio and Young's modulus).