This paper presents a physics-based control-oriented model for general floating offshore wind turbines that contains as many as six platform degrees of freedom (DOFs) and two drivetrain DOFs. The model is derived from the first principles, and therefore, can be manipulated by its real physical parameters while maintaining accuracy across the highly nonlinear operating range of floating wind turbine systems (WTSs). Forces and torques generated by wind and wave disturbances are derived for a baseline 5-MW wind turbine on a semisubmersible platform. The proposed model is validated against advanced simulation software FAST, and shown to be accurate at predicting major dynamics of the floating WTS.