Work results when a force acting on an object displaces it. It is equal to the product of the scalar component of force along the displacement direction. Mathematically, work can be given as the dot product of the applied force and the displacement of the object. The SI unit of work is the joule. One joule is the work done when a one-newton force displaces an object by one meter. Since work is a scalar quantity, its magnitude can be positive, negative or zero depending on the direction of the force relative to the displacement. Consider the example of a crane lifting a load upward. Here, the applied force and displacement vectors are aligned in the same direction, so the work done is positive. In another example, when brakes are applied to a moving car, the braking force acts in the opposite direction to the car's motion. Here, the work done is negative. A frictionless pulley lifting a load through a massless inextensible string does zero work as force and displacement are perpendicular.