It's called Physical Modelling, and it's a big sub-branch of audio synthesis. A very good intro is Perry Cook's "Real Sound Synthesis" book. To understand the

It's called Physical Modelling, and it's a big sub-branch of audio synthesis. A very good intro is Perry Cook's "Real Sound Synthesis" book. To understand the physics behind the software, the field you need to read is called Acoustics. A great intro (and the textbook we used in grad school) is "The Science of Sound" by Rossing et. al. (And +1 to Julius Smith book recommendations).