Lesson 3: Particles in Motion – We learned about kinetic molecular theory of matter which explains how particles move. The transfer of thermal energy depends on the movement of particles in the material. Then we learned that particles make up all matter and particles are in constant, random motion. Particles constantly collide with each other and with the walls of their container. Next we discovered that temperature is the measure of the average kinetic energy of the particles in material. If the particles in a material have little kinetic energy, the material feels cold. The SI unit for temperature is kelvin (K) and another temperature unit often used by scientists is Celsius (C).