The expression Five Elements describes a type of moving energy or body of Qi, rather than merely a physical element. They are really the Five Energies. The term “element” is used frequently even though it is not a true definition.
The five elements are Water, Wood, Fire, Earth and Metal. Everything in the universe is made up of one or a combination of these energies. These five energies are continuously interacting with one another; either in a productive, controlling or weakening cycle. An understanding of how these energies interact enables us to manipulate and use the available energies to their best advantage. 
While the elements can be represented in a physical state, the more you delve into Feng Shui you will discover that they can also be a personal characteristic, a body part, a number, a direction or one of several other attributes. For these reasons it’s important not to limit your thinking to just the physical.