The document discusses how the ear works and what sound is. It explains that the ear is made up of the outer, middle and inner ear. Sounds enter the outer ear as vibrations and hit the eardrum, causing it to vibrate. The vibrations are transferred through the middle ear bones (hammer, anvil, stirrup) to the inner ear where hair cells in the cochlea convert the vibrations into electrical signals that are sent to the brain. The document also provides diagrams of the ear and discusses how sound travels through molecules and air.