So just about everyone has played, or at least seen someone play a guitar before. But how does it work? Well in general, it's a pretty simple concept. You strum a string, or multiple strings, which creates a sound wave that enters the sound hole and is amplified inside the body when the sound waves enter the body and resonate within the wood. In order to get this to sound nice, however, the guitar needs to be tuned. In order for this to happen, several factors must be taken into account, suck as the mass, length, and tension in the string. when the guitar is in tune, the strings should each vibrate at a specific frequency. The A string should vibrate at a frequency of 110 Hz, and from there the other strings can be tuned to their respective frequencies. For example, the big E string can be tuned by pressing down on the A string (which should already be tuned to 110 Hz) at the 5th fret, and matching the frequencies. Tuning must be done often for several reasons, including the strings stretching out under the tension, the tuning pegs slipping, or even something as insignificant as a change in temperature, since we know that speed of sound changes based on the temperature. also, the design of the inside of the guitar, and even everything down to what kind of wood the body is made out of can affect the tone and overall sound of a guitar. Here is a video of a guitar being made to give a better idea of what exactly is going on inside the guitar. As you can probably tell, guitars are significantly more complicated than they appear on the outside, and a considerable amount of physics goes into them at every stage, from the basic design, to final materials used, to even every day use and tuning.