What are the three ways that thermal energy travels as heat?

Thermal energy travels as heat through convection, conduction and radiation. Convection is the transfer of heat by a liquid or gas, such as water and air, respectively. The movement of thermal energy by convection is called current.

Conduction is the transfer of thermal energy from one molecule to another. While conduction occurs in solids, liquids and gases, it works best in materials with simple molecular structures (i.e. where molecules are situated very close to each other). That's why metal is a better conductor than wood or plastic.

Radiation is the transfer of heat by electromagnetic waves. The sun is our greatest source of thermal energy, which it provides through radiation. When infrared radiation from the sun or other source strike an object, it causes the molecules within that object to move faster, effectively transferring its thermal energy, or heat, to that object. Radiators, irons, toasters and incandescent light bulbs are some examples of devices that radiate thermal energy.