I had Bruisma for 2 consecutive quarters (105A&B). Here are some things to consider before taking a class with "Ze Flying Dutchman". Pros: Prof. Bruinsma is the BEST lecturer I have encountered so far in my time at UCLA, or anywhere else for that matter. He genuinely wants you to learn, and will answer any question have about the material, regardless of how obvious/trivial until he is satisfied you understand. The tests are all curved with the average roughly set at a B-. (May not sound like a good thing, but when 60% on an exam gets you an A, it is.) His Dutch accent provides endless entertainment. (Don't worry, he's not difficult to understand.) Cons: The tests are all curved with the average roughly set at a B-. His tests are hard. Very hard. Every midterm had an average of 40-50%. He's a mathematical bad-ass, and tends to forget that undergrads typically aren't. Whatever subject the class is, you can be sure he will find every possible example that relates back to Holland or was discovered by some other crazy Dutchman. My opinion: Yes, his classes are hard, but they're hard for everyone. Since it's curved, all you have to do is beat the curve. No physics professor is going to just give away A's. Might as well take him, have an awesome, entertaining lecturer who will actually teach you something.
I would not recommend Prof. Fronsdal. The two main problems are 1) the material and 2) communicating with him. 1) In 105B, he did cover what most 105B classes generally would cover: Hamiltonian mechanics, collisions and Conservation of Momentum, gravitation and Kepler's Laws, scattering theory, special relativity, 4-vectors. However, in about 3, 4 weeks in, he introduces group theory (from Math 110A) and attempts to review some concepts from linear algebra (while bungling up various definitions) and differential geometry (generators of infinitesimal translations, rotations, etc.). The class takes a turn for the worse from that point on. If you want to cover topics sufficiently for usage in other classes (such as scattering theory for Physics 126), then you're stuck resorting to the not-so-great textbook that Fronsdal only refers to once a week (Marion and Thornton, Classical Mechanics). 2) Communicating with him is a problem. He wears a hearing aid, and I know it can't be helped, but . I attended his office hours almost weekly for homework questions. He will answer nearly anything you throw at him, but you'll find yourself raising your voice to the point where the rest of the faculty in the PAB 4th floor theory cluster will hear you. This is even worse in class when people attempt to ask him questions, and it may take as many as 2, 3 minutes to get the whole question across before he starts to address it. In the past several quarters that he's taught this class (the 105AB sequence), I feel like the students were lucky enough to have decent/good TAs who knew their material well or would invest their own time to consult Fronsdal on any mix-ups or anything simply not understood, and relay the message back to the students. He has a very generous grading curve, but don't let that fool you into thinking you'll get that much out of the class otherwise.
Fall 2020 - Note: took this class under remote conditions; hopefully, the reader is taking it in-person :) TLDR: Gelmini wants everyone to learn and is quite helpful but her exams are freaking impossible. Professor Gelmini is very enthusiastic and is always looking to help as much as possible. She is also very welcoming to feedback and is always trying to improve. Her office hours are very helpful, as she encourages questions and loves to see people finally understand things. She's very "motherly" and is a warm, wholesome person. One thing Gelmini lacks, however, is the ability to understand how much students actually understand the material. Professor Gelmini thinks we are all experts with the material. If she says an exam is meant to take an hour, it will probably take 3+ hours. Her first midterm was ridiculous, because it was literally find the formula in the notes, do some calculus on it, and get credit. If you didn't find the formula and tried to start with first principles (like the conservation of momentum), you wouldn't be able to solve anything. However, she curved that midterm very gently. And as always, she improved her second midterm (which was 24 hours). Even though I hate taking 24-hour physics exams (it's like 24 hours of torture), I think the questions on her second midterm were much fairer (although, the grading was a bit sus). Her final, however, was on another level. It was 24 hours of pain. I can't believe she gave that final. Worst part about it, the median was way to high. I wonder why. Anyway, Gelmini is a solid choice. Her exams are super tough, but I think this is the class where I have learned the most physics (so far). Good luck!
Fall 2018 - Honestly, this was the hardest class I took in the physics department here at UCLA, and I didn't learn much--way harder than 110B, 112, 18L, and the rest. Musumeci is a convoluted lecturer (probably because he treats us as though we already know the material), and the exams are unfair (derive the shape of a spinning planet, Euler angles of a satellite, etc). Suggestion: avoid.