What is internal energy defined as?

The correct answer is The total kinetic energy and potential energy of all particles in a system.

Exam lens: Write the relationship, substitute values only when needed, and finish by interpreting the result. This question asks: What is internal energy defined as. The correct response is The total kinetic energy and potential energy of all particles in a system, because internal energy combines particle kinetic and potential energy. In Internal energy, the marking point should connect directly to use particle motion and particle arrangement to describe changes in internal energy. If the question includes values, the working must keep the appropriate unit and operation; if it is an explanation, it must name the relevant particle behaviour or energy change. This item belongs to Internal energy and energy transfers, so avoid answers that switch to a different quantity, confuse heat with temperature, or describe gas pressure without collisions when collisions are the reason. Checkpoint 263 is distinct because it uses this exact question context and the exam lens rather than a generic particle-model sentence.