# What Is Work?

When we think of work, it usually involves exerting a force to cause some type of movement. Using this definition of work, we would consider the following to be work: a girl pushing a truck across the ground, a boy climbing over a fence, or a teacher lecturing to a class. While these examples are indeed work, there are also many things that we do that do not involve work in the scientific sense of the term. In order for work to be done, three quantities must be known: force, displacement and the angle between the force and the displacement.

In physics, the concept of work is very simple when motion and force are parallel. When they are, the resulting work is equal to the magnitude of the force multiplied by the distance moved. This is because the direction of displacement is the same as the direction of the applied force. The more force that is applied, the greater the amount of work that is produced.

However, when motion and force are not parallel, it becomes much more complicated. This is because the resulting work depends on the relative directions of the forces and the displacement.

For a work to be done, it must be either positive or negative. When a work is positive, it is equal to the product of the force times the distance moved. For example, if a ball is dropped from a height, the work done on it by the gravitational force as it falls is equal to its weight multiplied by its distance to the ground. This is because the direction of the force is perpendicular to the direction of the displacement.

On the other hand, if a person takes a book off of a shelf and then slides it back onto the shelf without moving the book, no work is done. This is because the direction of the motion is not the same as the direction of the force, so no work is done.

Work can also be described as the definite integral of power over a displacement vector, where the integral is defined along the trajectory from ph (t 1) displaystyle phi (t1) to ph (t 2) displaystyle phi (t2). For a variable force, this integral is computed by substituting the values of the force and the displacement into the equation above.

The SI unit of work is the joule, named after the 19th-century English physicist James Prescott Joule. Other non-SI units of work are the newton-metre, erg, watt, foot-pound, kilocalorie and liter-atmosphere. In addition, work can be measured in terms of its thermal energy content using units normally reserved for heat energy such as the calorie and the joule-calorie. However, these units are rarely used outside of thermodynamics. Generally, only the SI units of force and displacement are employed when talking about mechanical work. The use of other units is considered a mistake. Those who use them may be viewed as not being well informed of the principles of physics.