When you play an instrument what happens to the air inside?

Depending on the type of instrument, the air moves in a variety of ways to create various sounds.

In a woodwind instrument the air is directed by a mouth contact point (Saxophone = Neck, Flute = Lip Plate, Clarinet = Barrell). The air must be directed properly causing it to bounce back and forth along the body of the instrument. At the points of air contact, you will find holes. The various pitches are created by the hole remaining open or being sealed off via a pad made usually of felt covered in leather or fish bladder.

In a brasswind instrument the air is used differently. A brasswind instrument is constructed of various tubing diameters and lengths. As the air travels through the instrument valves are depressed which allows the air to pass through the correct tubings and make it's ay out of the bell of the instrument. The larger the tubing and the longer path that the air must travel to reach the bell, the lower the pitch that is created. These pitches can be fine tuned by using adjustable slides. Pulling the slide out will flatten (lower) the sound pitch. Pushing the slide in will sharpen (increase) the sound pitch.