Kinetic vs. Thermal energy What is the difference between kinetic energy and thermal energy? Is it the size of the particles or number of particles or is there some other defining factor?
 A: Depending on the level you're at, perhaps high school or after 16 level, then you're comparing macroscopic (i.e. something in our size scale) to something dependant on something microscopic (something on a particle level). The thermal energy is related to temperature, which is related to the average molecular/atomic KE of the particles within.
Furthermore, the ball is a (relatively speaking) more organised structure. Yet when examining thermal energy, the conceptual focus is on the particles themselves as objects.
To understand thermal energy, it is good to recall the concept of internal energy. The question above is typical of what I would ask at high school or grade 12/13 level to check for understanding. Internal energy, Hyperphysics
A: Kinetic energy is the total energy of a particle or system. For example a ball falling has kinetic energy. Thermal energy is a form of kinetic energy inside particles are at least subunits of bigger things. This thermal energy is just kinetic energy of particles. The size should be macroscopic to be considered kinetic and even this is depending on whether it is part of an even bigger thing or not.
https://www.britannica.com/science/thermal-energy
