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.

  • $\begingroup$ Not clear what your question is: (1) What is internal energy OR (2) Can an object be considered a 'system'. $\endgroup$
    – docscience
    Jun 14 '15 at 16:43
  • $\begingroup$ I am clear what internal energy is. It sounds like a conversion between kinetic and potential energy. $\endgroup$ Jun 14 '15 at 16:45
  • 2
    $\begingroup$ So then what is your question? That's what is not clear (to me) $\endgroup$
    – docscience
    Jun 14 '15 at 16:46
  • $\begingroup$ I am not clear. Sorry $\endgroup$ Jun 14 '15 at 18:42
  • $\begingroup$ here, 'system as a whole' = 'the objet'. $\endgroup$
    – user46925
    Jun 14 '15 at 22:35

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.

  • $\begingroup$ Is it like a water molecule in a glass water when you pour it in mid air? $\endgroup$ Jun 14 '15 at 18:43
  • $\begingroup$ I am having some difficulty in understanding your above sentence. $\endgroup$
    – SAKhan
    Jun 14 '15 at 18:47
  • $\begingroup$ That was just a analogy I saw on hyper physics. The definition of internal energy in my book is more like thermal energy converted from kinetic sorta thing. $\endgroup$ Jun 14 '15 at 18:58
  • $\begingroup$ Sure you can always convert kinetic energy to internal energy. Rubbing two stones for instance is a case in point. That will raise the temperature of stones. $\endgroup$
    – SAKhan
    Jun 14 '15 at 19:03

A system is a set of interacting or interdependent components that act as a whole, and the system's boundary delineates the system from its surroundings or environment in which it exists.

Wikipedia offers a good definition here.

If I'm understanding your question, you are asking whether objects, defined by their energy states, can be considered a system.

Certainly! The definition of a system can capture the energy states of any complex or ordinary object as interdependent, interacting components, and if suitable definitions for the input and output flow of energy.


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