Thermal energy is the term given to the energy that is lost and is not stored anywhere mechanically. This energy goes into a collection of unorganized molecules. A block of wood, a car, and a person are examples of organized collections of molecules. Air is an example of unorganized molecules. Example: A baseball player is running towards 2nd base. He decides to slide along the dirt into second base in order to avoid being tagged out. Unfortunately he starts to slide too early and comes to rest before reaching the base. When he was moving he had energy. As he slid into second base, he began to lose energy to the dirt and air.The energy went into heating up the dirt and then the dirt heated up the air above it. His energy cannot be recovered. Eventually the "lost" energy goes into moving the unorganized collection of molecules in the air. It has been transformed into thermal energy.

The term, "thermal energy," is a physicist's generic energy term used to describe when mechanical energy is lost. It can be accounted for by means beyond the scope of this text.

    A conservative force is where the energy associated with the force is dependent on position. Work done against a conservative force is stored as potential energy. Gravity is a conservative force. The higher a body is lifted , the greater the force stored in the gravitational field. When the body is released, its energy will be recovered in another form –kinetic energy.

A nonconservative force is where the energy is not recovered. It is lost. Usually as thermal energy. The path an object travels affects the amount of work. For example

Examples of conservative and non-conservative forces.