Thermal energy and heat are mainly related because of the fact that the faster molecules move, the more heat is created. If molecules are vibrating slower, that means that there will be less energy, resulting in less heat. Say I am boiling water. As the temperature increases, the water molecules move faster. Once that water cools, the molecules will be moving really slowly. In conclusion, thermal energy and heat are related because of how fast or slow the molecules move, the more or less heat and energy will be produced. I hoped this helped!
