Plastics wave Toward any tiny object, when we apply d Alembert theory, we must consider stress, body force and the inertia force of elastic objects caused by acceleration In space right-angle coordinate system, the x,y, z directions component of inertia force of every unite Ⅴ olume are: a2 02v 02w at at at Where p is the density of elastic objects9 Toward any tiny object , when we apply d’Alembert theory , we must consider stress , body force and the inertia force of elastic objects caused by acceleration . In space right-angle coordinate system, the x, y, z directions component of inertia force of every unite volume are: Where ρ is the density of elastic objects. 2 2 t u   −  2 2 t  −   2 2 t w   − 