Physics Programmer

I was wondering what a physics programmer does and how much the salary would be in the US (in the games industry)

We don't need them. Physics programming isn't some sort of mystical realm of coding, it's actually very simple. All game engines with APIs already have full physics system built into them, and in custom engines it's a really straightforward task to set up global gravity, force calculations, etc. In a game engine like Unity, for example, physics is all handled by rigidbodies, which essentially just use basic algorithms (y'know, rudimentary physics, p=mv, m1v1=m2v2, etc.). Since you're talking about salary, you obviously want to do this for the money, so you should really become a gameplay programmer. My company employs 4 gameplay programmers just to build the core features for one title, while the rest of my guys are AI coders, and UI devs, just to name a few. Most of my team are actually graphic staff (sound engineers, artists, and so on).

But if you're in it for the money, senior gameplay programmers are probably the best paid in the games industry. Following closely behind that are your server programmers.