Thermal energy is the total kinetic and potential energy in a substance that determines its temperature. Thermal energy is always transferred from warmer objects to cooler ones through conduction, convection, or radiation. Conduction involves the direct contact and vibration of particles between objects. Convection is the transfer of heat by the movement of molecules within a substance from warmer to cooler areas, such as wind or boiling water. Radiation transfers heat through space in the form of electromagnetic waves like the sun's rays.