This is the same principle where if you set off a tuning fork, a second fork of the same frequency will start to resonate and produce sound without coming into physical contact with the first. The closer you become to the specific energy, the more you will be able to work with it. Each element discussed also has symbols to represent them. One well known system consists of four triangles. Earth is an inverted triangle with a line through the middle, usually black or green in color.
Air is a point-up triangle with a line through the middle, and is yellow in color.
Fire is a point-up red triangle, and Water is a blue inverted triangle. Each of these symbols can give access to the respective elemental energies.