What is internal energy and how is it related to the particles in a system?

Internal energy is defined as the total kinetic energy and potential energy of all particles in a system. It reflects the energy stored within the system due to the motion and arrangement of its particles.

Particle lens: Describe arrangement, motion, spacing, collisions, or energy changes only when they are relevant here. This question asks: What is internal energy and how is it related to the particles in a system. The correct response is Internal energy is defined as the total kinetic energy and potential energy of all particles in a system. It reflects the energy stored within the system due to the motion and arrangement of its particles., because internal energy combines particle kinetic and potential energy. In Internal energy, the marking point should connect directly to define internal energy as the total kinetic energy and potential energy of all particles in a system. 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 216 is distinct because it uses this exact question context and the particle lens rather than a generic particle-model sentence.