Why is there no friction energy? Can anyone briefly explain to me why is there no term for frictional energy when they often referred to work done by friction instead? 
Thank you
 A: At the level of freshman mechanics, a good way to organize your thoughts is to realize that there are only a few forms of energy:


*

*kinetic energy

*gravitational potential energy

*electrical potential energy

*nuclear potential energy


It may seem as though there are other forms of energy, but they are really just manifestations of these forms, which exist at the microscopic level. Thermal energy is a form of random KE at the molecular level. Normal and frictional forces are basically electrical forces between atoms. Essentially all we have is KE plus one form of PE for each of the fundamental forces of nature.
This classification scheme does not work perfectly in general, e.g., it doesn't really work for describing the energy of an electromagnetic wave, or dark energy, but it works for anything you're going to do in the context of newtonian mechanics.
If I press on the sides of a box and lift it using a static friction force, the type of energy the box is gaining is gravitational PE, which is coming from the electrical PE being burned by my body's metabolism.
If a baseball player slides in to home base, the organized KE of their body is being converted into random KE (heat) by the kinetic friction force.
In the classification given above, all forms of energy are either energy of motion (kinetic energy) or energy of position (potential energy). Position means the position of one object relative to another object, when those objects are acting on each other at a distance through a force. For example, boiling water requires electrical PE, because you're taking molecules out of the liquid, separating them from the other molecules that were attracting them.
Mechanical work is just a transfer of energy by a macroscopic force. Any form of energy can be transformed into any other form of energy by mechanical work. Work itself is not a form of energy.
