Thermal energy is the energy associated with the random motion of atoms and molecules in a substance. It is a form of internal energy and is present in all matter, regardless of its state (solid, liquid, or gas). The higher the temperature of a substance, the greater its thermal energy.

Thermal energy can be transferred between objects through three mechanisms: conduction, convection, and radiation. Conduction is the transfer of thermal energy through direct contact between two objects. Convection is the transfer of thermal energy through the movement of a fluid (liquid or gas). Radiation is the transfer of thermal energy through electromagnetic waves.

Thermal energy is used in a variety of applications, including heating and cooling buildings, generating electricity, and powering vehicles. It is also a major source of energy for industrial processes, such as manufacturing and mining.

The study of thermal energy is called thermodynamics. Thermodynamics is a branch of physics that deals with the relationship between heat, work, and energy.