System and surroundings

As physical systems undergo change, one question always on the short-list is: What is happening with energy?

As the system changes configuration, what happens to the energy within the system and between the system and its surroundings?

Energy dissipation represents an important set of phenomena. In the context of Thermodynamics, we call it heat flow from the system.

Almost any real world transformation of potential energy into kinetic energy coincides with an exchange of energy between a system and its environment, usually as sound energy or heat flow. The friction on a block sliding down an inclined plane is a typical problem, leading to energy loss to the surroundings through heat flow.