The frequency or frequencies at which an object tends to vibrate with when hit, struck, plucked, strummed or somehow disturbed is known as the natural frequency of the object. When each of these objects vibrates, they tend to vibrate at a particular frequency or a set of frequencies. If you blow over the top of a pop bottle, the air inside will vibrate. If you pluck a guitar string, it will begin to vibrate. If you drop a meter stick or pencil on the floor, it will begin to vibrate. Nearly all objects, when hit or struck or plucked or strummed or somehow disturbed, will vibrate. The sound could be musical or it could be noisy but regardless of its quality, the sound wave is created by a vibrating object. Any object that vibrates will create a sound. The vibrating object that creates the disturbance could be the vocal cords of a person, the vibrating string and soundboard of a guitar or violin, the vibrating tines of a tuning fork, or the vibrating diaphragm of a radio speaker. The vibrating object is the source of the disturbance that moves through the medium. As has been previously mentioned in this unit, a sound wave is created as a result of a vibrating object.