In the simplest terms, work is the application of force to cause movement of an object over a distance. It is a scalar quantity that is defined by the magnitude of the force applied and the distance over which it is applied. Work is also the amount of energy that is transferred to or from an object when it moves, and it is a critical part of the concept of energy.
Work is all around us, from the push of a shopping cart to the lift of a book shelf. It is the reason why you can put a heavy box on top of the bookcase, but you would not be able to lift it over your head without the assistance of a crane. In fact, you would do more work lifting the box than holding it up over your head, because if you simply hold the weight above your head it does not change its distance over time, and thus does not transfer any energy.
One of the things that most people don’t know about work is how it relates to energy. The energy of something is the ability to do work, and it can be measured in joules (J). A unit of work is the newton-meter, N*m, which is equal to the amount of work done by a force of one newton over a distance of one meter in the direction of the force. Other units of work are often used, including calories and kilowatt-hours.
The most important thing to understand about work is that in order for a force to do work on an object, the object must be displaced. This means that, for example, when a teacher applies force to a wall and becomes exhausted, the teacher has not done any work because the wall shows no displacement. This is different from the way we think of work in everyday life, where lifting a heavy book up to your shoulder counts as work because it changes the position of the book.
Whenever an object is moved from one place to another, whether it is as large as an entire car or as small as a piece of paper, work has been done. This is because the motion of the object transfers energy to or from the system. In fact, all objects have potential energy, which is the scalar product of the force and the velocity of the object over its trajectory, and that energy can be converted to work through the use of the principle of conservation of linear momentum.
The fact that work can be done on a body is not limited to a change of position; it can also be the rotation of a shaft, the compression of a gas, or even the motion of internal particles due to an external magnetic field. For all of these, work can be calculated using the same formula as for a simple linear motion. This is called the path integral of the force-displacement relationship.
