Together they form the electromagnetic spectrum. These electromagnetic waves have different wavelengths and frequencies. The distance between one wave peak and the next one is called the wavelength. The number of these peaks that pass by you each second is called the frequency. Each of these colors has its own wavelength and frequency.
Mechanical energy is work or energy made by machines.
Today we use engines, powered by fossil fuels or renewable energy, to do work. Friction is a force that holds one object back against another. If you try to push a book along a table, at first it will not move. As you push harder, the book eventually begins to slide. But as the book rubs along the table, the force of friction slows it down.