Employing principles of classical mechanics to build up thermodynamics has been a hot topic for decades. Inversing this approach, this paper attempts to integrate classical mechanics into the present author's new thermodynamics. First, the concepts of heat and force are defined. Heat is the sum of molecular kinetic energy, system work, and system potential, while force is the linear gradient of heat variation. Since the heat variation can be divided into the exothermic and endothermal processes, the exporter and importer of force are clear. Hence, the forces' exports and imports are checkable. It solves the problem of Newton's "causes hitherto unknown." Second, Newton's three laws are rebuilt based on new definitions. The force equation has four terms of variation gradients: kinetic energy, temperature, gas molar volume, and liquid/solid molar volume. Only the gradient of kinetic energy variation creates the symmetric forces, i.e., mutual repulsion and attraction, though the reaction force doesn't exist. The reaction force is defined to represent the loss of kinetic energy. The other terms create asymmetric forces, namely that the force direction exported is opposite to that imported, which are the deriving forces of rotation and spin (self-rotation). Of most importance, these results relieve Newton's anxiety that the force transfer doesn't need a medium. Therefore, the origins and attributes of forces are disclosed. Third, as an outstanding achievement, a succinct equation is derived to predict the equilibrium distance of molecular interaction.