The thing about "weed-out" classes is that they're in some respects indiscriminate--to extend the metaphor, they sometimes spray so much curricular pesticide that they wipe out many people who might either *eventually* find the core skills and methods congenial or they underimagine what the core skills being laid out actually are in relationship to all the professional activities that have some relationship to that core.
The former point has become more and more intense for me over the years--as STEM departments have been under pressure to improve outcomes for underprepared students and to make their majors more inclusive, there have been more students who survive a "weed out" despite receiving poor grades in the lower rungs of the curricular hierarchy and maybe only barely making it through the major at all only to flourish spectacularly at a later date in a professional or scholarly role that rests on their undergraduate education. It means there really shouldn't be courses that are impassable barriers, especially in terms of what you're suggesting here--that since you can't have students engaged in the actual practice of a STEM field before they have the necessary preparation, you have to give them some feel for how challenging that practice is going to be, whereas many of the humanities and social sciences can set students to actual practice of their fields and disciplines from the get-go and just help them become more and more sophisticated in that practice over time.
But I also think many STEM faculty under-imagine what those end-state professional practices are in relationship to the discipline that they themselves work with. The relationship between primary care medicine and biology/biochemistry is more distant than a lot of faculty credit; the notion that organic chemistry is giving premed students a challenging window into their professional future and letting them decide whether they're going to find that life congenial just seems empirically untrue. If I really wanted to "weed out" future doctors before they get themselves deep in debt and find it's not the life they wanted, I'd compel them to endure the terrible conditions facing many residents, I'd have them deal with insurance adjusters telling them what they can and cannot offer as a standard of care, I'd have them spend a day listening to patients of all temperaments and presentations, and I'd have them spend a Saturday night in a crowded underfunded urban emergency room. The notion that organic chemistry is a good proxy test of what life as a basic physician (or other health-care professional) will be like just seems wrong. I think we try to tell ourselves that our assessments are good predictions of later professional competency, and I think for our own disciplines, that's absolutely true. I cannot imagine that someone who profoundly hated physics (or history) could perservere and become a skilled scholarly physicist or historian. But I can imagine someone surviving biology enough to do any number of jobs where biological science is somewhere present but not determinative of everyday professional practice. In some cases, this is not at all hypothetical--there's tons of evidence that barely-passing CS majors may end up being enormously successful tech designers or executives, barely-passing engineers may end up flourishing in industry or policy, etc.
Pre-med is a really odd case, because the profession has to a very large extent outsourced its weed-out classes to the Physics and Chemistry departments, subjects which as you note are largely ancillary to the practice of medicine. We see a little bit of the same thing with Engineering: our intro physics courses are full of future Economics majors who won't make it to a course in whichever subfield of engineering they arrived on campus as a nominal major of.
With regard to students who struggle early and flourish late, I've definitely seen that and arguably been one of those people. I agree this often reflects a too-narrow perspective about what major success means-- most of the cases I've seen involve students with a flair for experimental work who struggle with the more abstract math that's essential preparation for grad school in theoretical physics. And as you note, there are too many programs where the whole curriculum is exclusively focused on preparing students for graduate study in the discipline, rather than broader preparation for a career in something major-adjacent. I think that's less of a problem in the SLAC world, because the structure of the institutions makes it more likely for students to spread out their interests, but even in our corner of the academic universe, it's often a point of contention when designing curricula.
I agree with you that STEM fields do build on foundations, which end up serving as weed out classes. That being said, I also think the way of teaching physics that I experienced was designed for future physicists and not for a broader audience (eg. Engineers, other majors taking intro Physics). They often dove into the math rather than taking the pains to explain how it connects to real life.
Moving further into the course, us experimentalists experienced something similar from courses taught by theoreticians. For instance, we were taught Jackson, without explaining why and when the formal framework is needed. I finally got "weeded out" when I went for a QFT course in grad school, and even the first lecture wasn't explained in a way I could understand.
In professional life, I have found people of all backgrounds pick up a working knowledge of almost anything that relates to what they do. I think physics education has a lot of opportunity to make it more accessible to a wider audience.
Physics teaching is unfortunately highly variable, and I agree that as you move up the ladder things get more theory-focused. I think the presumption is that the future experimentalists peel off before you get to QFT, and go do things where they get their hands dirty. (As, in fact, I did, though I did take one "QED for Dummies" class...)
There's been a lot of good work in the Physics Education Research community about how to effectively connect with wider audiences, and I think the median intro course is slowly getting better. It's still a big range of quality, though.
I was very impressed by a physics colloquium on teaching physics by Joe Redish at UMD. Grad courses at UMD were actually great until I tried taking a QFT class.
The problem of intro physics classes designed for physicists only is not one that really exists in practice, certainly not today. At institutions that have substantial numbers of physics majors, there may be an intro class specifically designed for them, but then there are also intro classes designed for engineers. At most institutions, with smaller number of physics majors, the intro classes are targeted to the broader audience (often engineers, for calc-based, and bio/pre-med/pre-PT, for algebra-based). The standard textbooks are generally pretty light on math and derivations, and instructors often even lighter.
So it's often a complaint that exists more in the minds of students than in reality. I've had students complain that they couldn't possibly be expected to do the work asked of them in an intro lab - because they weren't physics majors. I have to point out to them that our intro labs are maybe 45% bio majors, 45% engineering majors, 8-9% other (exercise science, CS, math, chemistry, etc.), and about 1-2% physics majors. It turns out physics is challenging, even when it's a curriculum explicitly designed for those other than future physicists.
If you're an anglophone business major taking Japanese, you're going to find the course challenging even if it's oriented around business vocabulary and situations. Being interested in the applications helps, but marginally. It doesn't magically make it easy.
It seems like things have changed now, and I'm glad to hear of undergrad physics courses geared towards other majors. I would have imagined that it would have had a greater impact on students than what your experience has been.
But if you ever need a reminder of how things used to be taught (like my time), there's Jackson's textbook on electrodynamics, which a lot of physicists hate (though some surely love)
The thing about "weed-out" classes is that they're in some respects indiscriminate--to extend the metaphor, they sometimes spray so much curricular pesticide that they wipe out many people who might either *eventually* find the core skills and methods congenial or they underimagine what the core skills being laid out actually are in relationship to all the professional activities that have some relationship to that core.
The former point has become more and more intense for me over the years--as STEM departments have been under pressure to improve outcomes for underprepared students and to make their majors more inclusive, there have been more students who survive a "weed out" despite receiving poor grades in the lower rungs of the curricular hierarchy and maybe only barely making it through the major at all only to flourish spectacularly at a later date in a professional or scholarly role that rests on their undergraduate education. It means there really shouldn't be courses that are impassable barriers, especially in terms of what you're suggesting here--that since you can't have students engaged in the actual practice of a STEM field before they have the necessary preparation, you have to give them some feel for how challenging that practice is going to be, whereas many of the humanities and social sciences can set students to actual practice of their fields and disciplines from the get-go and just help them become more and more sophisticated in that practice over time.
But I also think many STEM faculty under-imagine what those end-state professional practices are in relationship to the discipline that they themselves work with. The relationship between primary care medicine and biology/biochemistry is more distant than a lot of faculty credit; the notion that organic chemistry is giving premed students a challenging window into their professional future and letting them decide whether they're going to find that life congenial just seems empirically untrue. If I really wanted to "weed out" future doctors before they get themselves deep in debt and find it's not the life they wanted, I'd compel them to endure the terrible conditions facing many residents, I'd have them deal with insurance adjusters telling them what they can and cannot offer as a standard of care, I'd have them spend a day listening to patients of all temperaments and presentations, and I'd have them spend a Saturday night in a crowded underfunded urban emergency room. The notion that organic chemistry is a good proxy test of what life as a basic physician (or other health-care professional) will be like just seems wrong. I think we try to tell ourselves that our assessments are good predictions of later professional competency, and I think for our own disciplines, that's absolutely true. I cannot imagine that someone who profoundly hated physics (or history) could perservere and become a skilled scholarly physicist or historian. But I can imagine someone surviving biology enough to do any number of jobs where biological science is somewhere present but not determinative of everyday professional practice. In some cases, this is not at all hypothetical--there's tons of evidence that barely-passing CS majors may end up being enormously successful tech designers or executives, barely-passing engineers may end up flourishing in industry or policy, etc.
Pre-med is a really odd case, because the profession has to a very large extent outsourced its weed-out classes to the Physics and Chemistry departments, subjects which as you note are largely ancillary to the practice of medicine. We see a little bit of the same thing with Engineering: our intro physics courses are full of future Economics majors who won't make it to a course in whichever subfield of engineering they arrived on campus as a nominal major of.
With regard to students who struggle early and flourish late, I've definitely seen that and arguably been one of those people. I agree this often reflects a too-narrow perspective about what major success means-- most of the cases I've seen involve students with a flair for experimental work who struggle with the more abstract math that's essential preparation for grad school in theoretical physics. And as you note, there are too many programs where the whole curriculum is exclusively focused on preparing students for graduate study in the discipline, rather than broader preparation for a career in something major-adjacent. I think that's less of a problem in the SLAC world, because the structure of the institutions makes it more likely for students to spread out their interests, but even in our corner of the academic universe, it's often a point of contention when designing curricula.
I agree with you that STEM fields do build on foundations, which end up serving as weed out classes. That being said, I also think the way of teaching physics that I experienced was designed for future physicists and not for a broader audience (eg. Engineers, other majors taking intro Physics). They often dove into the math rather than taking the pains to explain how it connects to real life.
Moving further into the course, us experimentalists experienced something similar from courses taught by theoreticians. For instance, we were taught Jackson, without explaining why and when the formal framework is needed. I finally got "weeded out" when I went for a QFT course in grad school, and even the first lecture wasn't explained in a way I could understand.
In professional life, I have found people of all backgrounds pick up a working knowledge of almost anything that relates to what they do. I think physics education has a lot of opportunity to make it more accessible to a wider audience.
Physics teaching is unfortunately highly variable, and I agree that as you move up the ladder things get more theory-focused. I think the presumption is that the future experimentalists peel off before you get to QFT, and go do things where they get their hands dirty. (As, in fact, I did, though I did take one "QED for Dummies" class...)
There's been a lot of good work in the Physics Education Research community about how to effectively connect with wider audiences, and I think the median intro course is slowly getting better. It's still a big range of quality, though.
I was very impressed by a physics colloquium on teaching physics by Joe Redish at UMD. Grad courses at UMD were actually great until I tried taking a QFT class.
The problem of intro physics classes designed for physicists only is not one that really exists in practice, certainly not today. At institutions that have substantial numbers of physics majors, there may be an intro class specifically designed for them, but then there are also intro classes designed for engineers. At most institutions, with smaller number of physics majors, the intro classes are targeted to the broader audience (often engineers, for calc-based, and bio/pre-med/pre-PT, for algebra-based). The standard textbooks are generally pretty light on math and derivations, and instructors often even lighter.
So it's often a complaint that exists more in the minds of students than in reality. I've had students complain that they couldn't possibly be expected to do the work asked of them in an intro lab - because they weren't physics majors. I have to point out to them that our intro labs are maybe 45% bio majors, 45% engineering majors, 8-9% other (exercise science, CS, math, chemistry, etc.), and about 1-2% physics majors. It turns out physics is challenging, even when it's a curriculum explicitly designed for those other than future physicists.
If you're an anglophone business major taking Japanese, you're going to find the course challenging even if it's oriented around business vocabulary and situations. Being interested in the applications helps, but marginally. It doesn't magically make it easy.
It seems like things have changed now, and I'm glad to hear of undergrad physics courses geared towards other majors. I would have imagined that it would have had a greater impact on students than what your experience has been.
But if you ever need a reminder of how things used to be taught (like my time), there's Jackson's textbook on electrodynamics, which a lot of physicists hate (though some surely love)