# 22.2: Introduction


The amount of kinetic energy, the amount of movement, is what determines how hot or cold something seems to be.  If particles (atoms or molecules) have a relatively high average kinetic energy, then the material will feel hot.  If particles have a relatively low average kinetic energy, then the material will feel cold.  We may not be able to see the movement, but even solid objects have particles that are vibrating and may have translational motion.  When two materials with different temperatures come into contact, they will come into thermal equilibrium.