Energy naturally flows from a hot body to a cold body. When energy flows from a hot body to a cold body, we say that the hot body has heated the cold body. For example, energy naturally flows from a hot Bunsen burner flame to a cold beaker of water placed above it. The flame has heated the beaker of water.

There are three basic mechanisms by which heating can occur. These are conduction, convection and radiation^*.

• Conduction
• Convection
• Radiation