[Physics] internal energy

Question

My physics book says:

The total potential energy and kinetic energy possessed by the particles that make up an object, but excludes the potential and kinetic energies of the system as a whole.

I wonder if the object can be seen as a system.

Answer 1

Excludes the system as a whole means you disregard the kinetic energy associated with the translation or rotation of the body as a whole. For instance that associated with the center of mass motion. In case of internal energy you focus on the interior, like motion due to the atoms and molecules of which the object is made up of.