Work is a noun meaning your job or the activities you do in your job. It can also be a verb meaning to perform labor, effort or exertion, especially hard work. It can also refer to a specific activity, such as typing or painting, that takes a lot of physical effort or concentration. Work can also be a slang word that means something difficult or unpleasant.
In physics, work is the action of force that causes an object to change its position, which is measured in terms of displacement (distance moved) or velocity (speed). Work is equal to the amount of force exerted multiplied by the distance over which the force is applied. The direction of the force and the direction of the displacement determine whether the work is positive, negative or zero. In other words, work is the transfer of energy from one object to another. It can also be considered a measurement of energy, and its units are the same as those for energy: the SI unit is the joule (J), named after 19th-century English physicist James Prescott Joule. Other non-SI units include the newton-metre (Nm), erg, foot-pound and kilowatt hour.
If the direction of the force and the direction of the change in position are the same, the work is positive. This would be the case, for example, if someone pushed a rigid brick wall, tiring himself but not changing the location of the wall. However, if a book falls freely from a table due to gravity, this is considered to do work because the book moves downwards.
Conversely, if the direction of the force is opposite to the change in position, the work is negative. This is the case if someone lifts a heavy box onto their shoulder, because it takes a great deal of effort to hold the box up against the weight of gravity.
There are also cases where it is not possible to do work. If an object is already at its final position, for example, when a person throws a ball upwards, then no work is done because the force of gravity has achieved its goal. The same applies if an object is moving at a constant speed over a given distance, such as a car travelling along a highway, where the force of the road is constant. In these cases, no work is done because the net change in position is zero. However, if the force is continually increasing over a given distance, then work is being done. This is because the force is continuously adding energy to the object, thereby accelerating it forwards. However, the energy that is added to the object can eventually be removed by friction, or by a gravitational field, and the acceleration will decrease. In this case, the work is still being performed. Nevertheless, the acceleration will eventually be zero. This is why it is important to use smooth, continuous forces. Otherwise, the acceleration will become uncontrollable.