Work

Work is the transfer of energy.

In physics we say that work is done on an object when you transfer energy to that object. If you put energy into an object, then you do work on that object.

If a first object is the agent that gives energy to a second object, then the first object does work on the second object. The energy goes from the first object into the second object. At first we will say that if an object is standing still, and you get it moving, then you have put energy into that object. Mechanical work is the amount of energy transferred by a force acting through a distance. The term work was first coined in 1826 by the French mathematician Gaspard-Gustave Carioles. If the resultant force F on an object acts while the object is displaced a distance d, and the force and displacement act parallel to each other, the mechanical work done on the object is the product of F multiplied by d. If the force and the displacement are parallel and in the same direction, the mechanical work is positive. If the force and the displacement are parallel but in opposite directions (i.e. antiparallel), the mechanical work is negative.

However, if the force and the displacement act perpendicular to each other, zero work is done by the force

The SI unit of work is the joule (J), which is defined as the work done by a force of one Newton acting over a distance of one meter. The dimensionally equivalent Newton-meter (N*m) is sometimes used instead; however, it is also sometimes reserved for torque to distinguish its units from work or energy. Work can be zero even when there is a force. The centripetal force in a uniform circular motion, for example, does zero work since the kinetic energy of the moving object doesn't change. This is because the force is always perpendicular to the motion of the object; only the component of a force parallel to the velocity vector of an object can do work on that object. Likewise when a book sits on a table, the table does no work on the book despite exerting a force equivalent to mg upwards, because no energy is transferred into or out of the book