We make sounds by actions such as striking, blowing, plucking and scraping

Young children playing guitars in class.

To create sound, you need an input of energy in the form of movement. An object is struck, scraped or blown into and vibrates as a result. The vibrations cause intermittent variations in pressure in both the object and the substance surrounding it – for example, air or water. If nothing moves, there are no vibrations. If there are no vibrations, there are no changes in pressure in the surrounding substance to travel away and be picked up as sound.