A small part of the universe to which applies the laws of thermodynamics.We call this subset a SYSTEM.
The thermodynamic system is analogous to the free bodydiagram to which we apply the laws of mechanics, (i.e.Newton’s Laws of Motion).
The rest of the universe outside the system close enough to the system to have some perceptible effect on the system is called the surroundings.
The surfaces which separates the system from thesurroundings are called the boundariesas shown in above fig (eg: walls of the kettle, the housing of the engine).
