In this paper, we investigate inherent mesoscale spatial fluctuations of the coefficient of friction (COF) in dry frictional phenomena by modelling it as a random field. The statistical properties of the resulting global random forces and torque are derived for three types of interface motion: pure translation, pure rotation and general planar motion. Closed-form formulas are derived for the case where the interface has a square geometry and a numerical simulation method is developed for more complex shapes. The analysis of these results shows that the statistical properties of the global forces and torque are functions of the ratio of the correlation length of the random field to the characteristic length of the interface, which enables limit analyses to be performed with respect to this ratio. These analyses provide guidance regarding whether the coefficient of friction should be modelled as a random field, a random variable or a deterministic variable. The concepts developed in this paper are illustrated through a simple crank-slider model for which the statistics of energy dissipated (because of the friction) are analysed concerning the value of the ratio of the correlation length to the sliding surface size.