Work:

Work is the transfer of energy.

Work is done on the object when you are transferring energy to that object. If you put energy into an object, then you are performing work on that object.

If a 1st object is the agent which gives energy to a second object, then the 1st object does work on the 2nd object. The energy goes from the 1st object into the 2nd object. At 1st we will say that if an object is standing still, and you get it moving, then you have put energy into that particular object.

The Mechanical work is the amount of energy transferred by force acting through a distance. The term work was first coined in the year 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 displacement and force 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 same direction, mechanical work done is positive.

But, 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 sometimes reserved for torque to distinguish the unit of it from work or energy. Work can be 0 even when there is some force exerted. The centripetal force in the uniform circular motion, for instance, does zero work as the kinetic energy of the moving object doesn't change. This is because the force is always perpendicular to the motion of object; the component of a force parallel to velocity vector of an object can do work on that object. Similarly when a book sits on a table, the table does not work on the book despite exerting a force equivalent to mg upwards, as no energy is transferred into or out of the book.