Here's why:
* Internal energy is the sum of all the kinetic and potential energies of the particles within a system.
* Kinetic energy is the energy of motion, so the kinetic energy of the particles contributes directly to the internal energy.
* Potential energy arises from the interactions between particles (like electrostatic forces). While not strictly "kinetic," it still plays a role in the overall energy of the system.
Therefore, internal energy encompasses the total energy associated with the motion and interactions of particles within a material.
