== Equation ==The equation used to model belt friction is, assuming the belt has no mass and its material is a fixed composition:: formula_1where formula_2 is the tension of the pulling side, formula_3 is the tension of the resisting side, formula_4 is the static friction coefficient, which has no units, and formula_5 is the angle, in radians, formed by the first and last spots the belt touches the pulley, with the vertex at the center of the pulley.