When a force acts on an object and the object actually moves in the direction of force, then the work is said to be done by the force. Work done by the force is equal to the product of the force and the displacement of the object in the direction of force. If under a constant force F the object displaced through a distance s, then work done by the force W = F * s = F s cos θ where a is the smaller angle between F and s. Work is a scalar quantity, Its S1 unit is joule and CGS unit is erg. ∴ 1 joule = 107 erg Its dimensional formula is [ML2T -2 ]. Work done by a force is zero, if (a) body is not displaced actually, i.e., s = 0 (b) body is displaced perpendicular to the direction of force, i.e., θ = 90° Work done by a force is positive if angle between F and s is acute angle. Work done by a force is negative if angle between F and s is obtuse angle. Work done by a constant force depends only on the initial and final Positions and not on the actual path followed between initial and final positions.