How does physics relate to music?
Standing or stationary waves.
Musical instruments produce standing waves that correspond to particular musical notes.
Stringed instruments such as pianos and guitars produce transverse standing waves. The instrument has strings with a variety of carefully tuned masses and lengths to produce the necessary waves. On a guitar the strings can be pressed against the fret board to create a string with a new length and therefore a new set of standing waves.
Wind instruments such as saxophones and clarinets have carefully designed air columns that are tuned to produce longitudinal standing waves. Operating the buttons and levers the instrument forces the position of antinodes and therefore which standing wave is produced. Therefore by controlling the production of waves the production of musical notes is controlled.
If you'd like to see a visual representation of this I made a video of the Ruben's Tube: .