Very often, people think that complicated things are difficult to explain but they do not realise that the simplest things are in fact the hardest things to explain. Take a piece of music for example. One may be amazed at how a composer puts together all the different pitches and timbres to make a beautiful piece. It may be difficult to explain, but the basic components which makes that up is sound. How is sound formed? Why does vibrations produce sound, or rather, how does the contration and expansion of molecules give out sound?