Work and energy

Work can be defined as the application of a force over a distance. In other words, work is the use of a force to move an object a certain distance. The equation for work done is:

W = Fs

where W is work done, F is force in newtons (N) and s is the distance the object moved in metres (m). Work is measured in joules (J), which is equivalent to one newton per metre.

Work takes on many forms. It can be most easily seen when an object is moved from one place to another. Work is also taking place, however, when an object is being heated or changes state. In these cases, the work takes place on a particle level. As particles move more quickly, the object heats up and changes state.

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Energy is the ability of an object to change the velocity, location, shape or state of another object. Simply put, in many cases, energy is the ability of an object to do work. Some definitions of work state that it is a transfer of energy from one object to another. Like work, energy is measured in joules. There are two main types of energy: kinetic energy and potential energy.

Kinetic energy is the energy found in objects that are in motion. Kinetic energy is often used to change the speed or shape of another object. A billiard ball being hit by another billiard ball, for example, shows kinetic energy being used to change the speed of another object. Another example of kinetic energy doing work is when two cars collide with one another and their shape is changed.

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Potential energy is energy that is stored within an object. There are many kinds of potential energy. The most common example is gravitational potential energy, which is the energy an object gains when it is raised higher in a gravitational field. There are other types of potential energy that will be discussed later. (Refer Chapter 4)

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Potential energy can be transformed into kinetic energy and vice versa. Imagine raising a ball into the air. As the ball is raised, it gains gravitational potential energy. If you were to let go of the ball, it would start to fall towards the ground. As it starts moving, the ball's potential energy becomes kinetic energy. Conversely, if the ball were to bounce up into the air after it hit the ground, its kinetic energy would be transformed into potential energy.