Cambridge Natural Sciences for physics

My personal view on this is unless you have an interest in studying something like Evo&behaviour or Earth Sciences (materials is pretty deeply rooted in Chemistry, so while it may not require the subject it would very much surprise me if someone only liked Materials and not Chemistry) - then just apply for the Maths course with Physics instead of NatSci.

With Compsci now gone; there is, in my opinion, no reason to subject yourself to IA NatSci if you know you are going to do Physics. The IA Maths course is also much better and more rigorous preparation for a prospective physicists or theoretical physicist (a theoretical physicist should honestly do the full undergrad degree in Maths and then look to do a PhD in applied Maths/ Physics). IA Natsci is more raw work than IA Maths, covers the same amount of Physics, and covers less Maths.

STEP seems like a good reason, as does avoiding real maths. I don't think the lack of CompSci changes much, my understanding is that it wasn't a hugely popular choice (and not hugely popular among the people who did it either). My impression is that people who do Earth or Materials often enjoy them even if they weren't interested to start with because they're taught well. I'm not sure Maths with Physics and PhysNatSci are interchangeable for that many people. I thought most people doing the former consider IA to be basically normal maths (they often study the extra paper anyway) with some physics on the side, whereas for PhysNatScis the 1/4 physics paper takes up a lot more than 1/4 of their time/effort.

The Cambridge Maths course is very applied. Things like Galois theory are really important to Physicists, I really don't see why not studying them from a fundamental level is meant to be a good thing for prospective physicists. It's definitely the best possible foundation to build a research career on - and this is the reason why the vast majority of modern names in Physics do not actually have Physics undergraduate degrees, they have Maths degrees (and often their PhDs are also firmly rooted in Maths more than theoretical methodology).

Avoiding STEP because you think you might fail it is just a massive red flag. Quite a lot of Mathmos end up in part II natsci physics and the natscis who get into it through their IA/ IB grades are also going to be very strong at applied maths. Cambridge grading is competitive, so if you don't measure up well against these people (who would definitely have been on track to get at least 1,2 in STEP) you are going to really struggle to get out with a 2i. It's definitely a lot better to fail STEP and do well in another University, than to try and dodge STEP just so you can get into a University where you can't keep up with the rest of the year.

Maths w/ Physics is simply the better route into Physics. What you give up is the option of studying something like Earth Sciences. Again, like my original post said, if you have an interest in doing this then that's fine. But if you are just going to choose modules to make up the numbers, it makes a lot more sense to be doing Maths in that time instead. Again, it's completely normal to do Maths w/ Physics => switch to 2nd year NatSci doing Physics. But doing Maths w/ Physics also just lets you continue with Maths for longer.

And yes, IA full Maths + Physics is a lot less work than IA NatSci. In terms of studying hours, in terms of # of supervisions, in terms of contact hours, in terms of lecture hours. The IA option for something like "chemistry" or "materials" is going to cover the same volume of content as a full 1st year undergraduate course at another University - and it's also going to happen at what cambridge considers to be a difficulty capable of stretching its students. But IA Natsci Maths is not the same as a full first year maths undergrad degree since it largely skips a large amount of the theory and just tries to focus on teaching A-Level FM properly and doing foundations for physics. Likewise for IA Maths the actual content is going to be largely the same as first year Maths at Bristol, Imperial, Durham, etc. - but the problems will be harder, there will be set supervision work, there will be much harder exam questions - because it's cambridge. Of course doing first year physics is less work if you are independently already studying PDEs, complex analysis, field calculus, mechanics and special relativity in your Maths degree.

Just to add to the mix: NatSci has Saturday lectures in Year 1.

Maths too no?