Consider a flat belt wrapped around a set of pulleys, experiencing belt tensions at the driving pulley ends. For a counterclockwise pulley motion, the magnitude of T2 is greater than T1 due to the friction between the belt and pulley surface. Knowing the total angle of belt-to-surface contact and coefficient of friction enables the estimation of the tensions. A free-body diagram of a differential element AB of the belt is drawn. Assuming impending motion, the frictional force opposes the sliding motion of the belt, causing the magnitude of the belt tension acting at point B to increase by dT. Applying the horizontal and vertical force equilibrium and using the cosine and sine approximations, two force equilibrium equations are obtained. The product of two differentials compared to the first-order differentials is neglected in the vertical equilibrium equations, while the horizontal equilibrium equation is simplified further. Combining the equilibrium equations and integrating between the corresponding limits gives an expression correlating the belt tensions. This equation applies to flat belts passing over any curved contacting surface.