I find the physics tag very unclear on a site like this. It's been used on questions about physical aspects like bow length, a couple physiology questions, and several questions about sound such as this one. With such breadth, it's useless.
I also think regardless of how it could be narrowed, it will just serve to confuse users. Most don't read tag wikis so the particular meaning we assign may not be known, and even then it may be mis-applied. The definition that most readily comes to mind is "the nature and properties of matter and energy", which is again awfully broad.