
The atoms or molecules that make up substances are always vibrating as a result of thermal energy. When a substance is hotter, that means its atoms or molecules are vibrating faster. Thermal energy always moves from a hotter area to a colder area. Adding or removing thermal energy can cause a substance to change from one state to another, and chemical reactions can cause thermal energy to increase or decrease.
To better understand thermal energy…
LET’S BREAK IT DOWN!
What is thermal energy?

All matter is made up of particles, either atoms or molecules, and these particles are constantly vibrating. The energy of these moving particles is called thermal energy and is related to the temperature of the substance. Temperature measures the average kinetic (or motion) energy of the particles within a substance. Temperature measures an average because the particles within a substance do not all move at exactly the same speed. The particles in hotter substances are moving faster, whereas the particles in colder substances are moving slower.