In everyday use, work is the effort that an individual or group makes to accomplish a task. The word can also be used to describe the act of transferring energy from one object to another, or changing its form. In physics, however, the concept of work is more scientific, and it involves a force exerted on an object and the resulting displacement of that object. A person holding a heavy book over his head, for example, would not be doing work in the physics sense because the force is not directly proportional to the distance that the book moves.
A key part of physics’ definition of work is that it must be done on an object to change its energy from potential to kinetic. This can happen in a variety of ways, including when a ball is dropped and it gains kinetic energy as it falls to the ground; when a horse pulls a plow across the field; or when an Olympian throws a shot-put.
Work also changes the amount of mechanical energy an object has, and can be transferred from one object to another. For example, if someone picks up a box that weighs 10 pounds and then drops it onto a carpet, the box will gain 10 times as much kinetic energy as it had before picking it up. This is because the total force exerted by the hand over this time and distance, multiplied by the mass of the box, is equal to the change in energy of the box.
The term work is often applied to a particular job or profession. For example, some people may be called on to do manual labor for a living, while others may be employed in the computer industry and are known as IT technicians. Traditionally, IT departments have focused on the design, installation, maintenance and repair of computers and related hardware components, but they are now increasingly tasked with managing the flow of data between people and devices.
While some examples of work seem intuitive, it can be difficult to define exactly what work is in the physics sense. A horse pulling a plow across a field, for instance, does positive work because the force exerted on the plow is greater than the displacement it causes. A man pushing a large boulder across the floor, on the other hand, does no work because the force exerted is not equal to the displacement it produces.
Whether something is doing work or not, its effects are measured in units of energy—in the SI (International System of Units) system, joule; and in the centimetre-kilogram-second system, erg. The energy of an object, either kinetic or potential, is equal to the product of its force and its displacement, regardless of its direction. This property of work is called its tensor, or vector, magnitude. Because work is a vector quantity, it has both magnitude and direction, even though we tend to think of it as a scalar, or non-vector, magnitude.