Section+4.4+-+The+Law+of+Conservation+of+Energy

Recall that the law of conservation of energy states that:


 * Energy cannot be created or destroyed; rather, it can be **transformed** into different types of energy, and **transferred** from one place to another
 * The total energy within an **isolated** system remains constant (i.e. energy in an isolated system is conserved)

Energy falls into two main categories:


 * Kinetic energy: the energy of **motion**
 * Potential energy: the energy **stored** by matter based on its position of the arrangement of its atoms/molecules

Examples of **kinetic** energy include:


 * Heat/thermal energy (this is kinetic energy at the microscopic level)
 * Sound energy (transmitted through the motion of particles)

Examples of **potential** energy include:


 * Chemical potential energy (energy stored in chemical bonds)
 * Gravitational potential energy (energy stored by matter based on its vertical height relative to a surface; matter is under the influence of gravity)
 * Radiant energy (the energy stored by electromagnetic waves, such as visible light)
 * Elastic potential energy (energy stored within an elastic device that is stretched, compressed, twisted or bent)


 * Total mechanical energy** is the sum of the **kinetic** energy and the **gravitational potential** energy. Mechanical energy also follows the law of conservation of energy.

Friction causes kinetic energy to transform into heat/thermal energy. As such, there are very, very few situations (in the "real world") in which the transfer of energy is 100% efficient.

"Whenever kinetic friction does negative work to slow an object down, the magnitude of the work equals the thermal energy produced" (Nelson, p. 199)


 * Work done by friction, W = -F_k * (delta) d
 * Therefore, thermal energy produced by friction, E_th = +F_k * (delta) d