AP Physics on Monday!

[drummerdude13903]

Hey, I know that Randall is a physics major, and a lot of people here are big in science and math, so I think we should wish the best of luck to all the daily xkcd vistors that will be taking the AP Physics B and AP Physics C exam on monday across the country! Today's comic is a great one for the upcoming occasion too!

[themandotcom]

Good luck fickle high school students! I remember being super stressed for these AP exams, but don't worry - it won't really matter much. And the top schools don't even take AP credits! ><

[KestrelLowing]

Good luck fickle high school students! I remember being super stressed for these AP exams, but don't worry - it won't really matter much. And the top schools don't even take AP credits! ><

Yeah, but I wonder how much of that is just "Hey, look at us. We're so good we don't even accept AP scores!" and how much is legitimate belief that the AP tests do not cover enough well enough.

Still good luck to you guys! Make sure you know your formulas. Unless it's changed, you don't get the sheet for multiple choice

[existentialpanda]

Yeah, but I wonder how much of that is just "Hey, look at us. We're so good we don't even accept AP scores!" and how much is legitimate belief that the AP tests do not cover enough well enough.

Can't speak for every school, but at mine it's because the introductory classes are already at a high enough level that an AP-level course is not an adequate replacement. A lot of people here (myself included) got 5s on all our tests, took the first-level classes anyway and hell, if I'd tried to skip them I'd have died. Make of that what you will.

Also, good luck to all you people who still have to worry about that. See you on the other side.

[Wodashin]

I think you get a different sheet for the multiple choice.

This is my first AP test ever, and I've heard it's the toughest one. Hoping to do well, and good luck to everyone else.

I've never studied before, but I think if I want to get a 5 I should. We had a mock AP test that was one from a few years back and I got a 4.

Damn you Thermodynamics and Pressure, and the flu. Mainly the flu, but because of it, the other two things. Super stressed.

Soooo... This test isn't all that important

[doogly]

Good luck fickle high school students! I remember being super stressed for these AP exams, but don't worry - it won't really matter much. And the top schools don't even take AP credits! ><

Yeah, but I wonder how much of that is just "Hey, look at us. We're so good we don't even accept AP scores!" and how much is legitimate belief that the AP tests do not cover enough well enough.

Still good luck to you guys! Make sure you know your formulas. Unless it's changed, you don't get the sheet for multiple choice

The AP does not cover enough. At Dartmouth, a good score on the AP physics allowed you to take the honors intro sequence, which does in 3 terms what a slower paced one does in 4. But the first two are still certainly mechanics and e&m done properly.

[drummerdude13903]

Good luck fickle high school students! I remember being super stressed for these AP exams, but don't worry - it won't really matter much. And the top schools don't even take AP credits! ><

Yeah, but I wonder how much of that is just "Hey, look at us. We're so good we don't even accept AP scores!" and how much is legitimate belief that the AP tests do not cover enough well enough.

Still good luck to you guys! Make sure you know your formulas. Unless it's changed, you don't get the sheet for multiple choice

yep, there are no reference tables for the first half. memorizing all the formulas is the worst part.

[Bakemaster]

If you take issue with having to memorize formulas for your AP Physics test, you're definitely not ready to skip over the actual college physics coursework. In college you'll not only be expected to memorize the formulas, but likely to derive them as well, and you'll be tested on it.

[Wodashin]

Welp, it's today. And I studied for 0 minutes. It doesn't surprise me, but I'm screwed. Well, I'll still pass, but I'll only pass. I'm not getting a 5 for sure.

Good luck to everyone out there taking this test today.

[KestrelLowing]

If you take issue with having to memorize formulas for your AP Physics test, you're definitely not ready to skip over the actual college physics coursework. In college you'll not only be expected to memorize the formulas, but likely to derive them as well, and you'll be tested on it.

Eh, I had a different experience. Once I hit college, the majority of my classes allowed either a common formula sheet or they allowed you a sheet to make one yourself. If you think about it, that's how the real world is going to be. You're never going to be asked to calculate something on the spot. You just need to know that said formulas exist and how to use them. You don't actually need to have them memorized.

Of course just by using some enough, you'll have them memorized. Still, I always found it stupid that you would have to memorize formulas when that's not how the 'real world' works.

[Bakemaster]

The issue isn't whether you'll be required to memorize them in the real world or not, though; it's about training people to have a certain level of mastery over the subject. You're not required to never make a mistake in most real world careers, either, but we should be able to agree that one goal of college study is to gain the ability to make very few of them, and infrequently. Thus, you get marked down fairly consistently for making mistakes on tests, where in the real world you would just be told you screwed it up, now you fix it.

I'm not saying students necessarily will be (or should be) required to memorize things like the many formulas for electric field produced by differently-shaped charge distributions, but they absolutely need to memorize things like Coulomb's Law and Gauss's Law and if they're in a STEM field it's pretty important that they know how to use the fundamental laws to derive specific formulas.

[KestrelLowing]

The issue isn't whether you'll be required to memorize them in the real world or not, though; it's about training people to have a certain level of mastery over the subject. You're not required to never make a mistake in most real world careers, either, but we should be able to agree that one goal of college study is to gain the ability to make very few of them, and infrequently. Thus, you get marked down fairly consistently for making mistakes on tests, where in the real world you would just be told you screwed it up, now you fix it.

I'm not saying students necessarily will be (or should be) required to memorize things like the many formulas for electric field produced by differently-shaped charge distributions, but they absolutely need to memorize things like Coulomb's Law and Gauss's Law and if they're in a STEM field it's pretty important that they know how to use the fundamental laws to derive specific formulas.

Yeah, I really can't remember the Navier-Stokes equations, but I know it relates to fluid flow, deals with conservation of momentum, and I know exactly where to find it (don't sell back good/mediocre textbooks!). Still, I know how to use it. (At least in relatively simple cases where a lot of stuff cancels! - Haven't taken compressible flow and don't really plan to)

And yes, being able to derive formulas is fairly important, but once again I think it's another "do this once, see what assumptions are made, file that in the back of your head somewhere, and look it up when you need it". The skill of being able to derive relationships is very important, but remembering exactly how to do it for specific formulas, not required.

You've hit something that I really feel strongly about: You should never be forced to memorize anything specific. By that, I mean that you should be able to do the processes that are necessary for math or physics or whatever, but the specifics that can easily be found in a text book shouldn't be required. You should certainly know they exist and what terms are in it, but (and this example is very simplistic and could easily be figured out with unit analysis) if you know Ohms law relates voltage, current, and resistance but just can't remember if it's V=IR or V=I/R, why does that matter?

Yes, there is definitely personal bias here. I cannot memorize equations or anything like that for the life of me. If I use it enough and it's easy enough, maybe. I don't have my multiplication tables memorized. I just cannot remember things of that nature. Processes though? Those are really easy and I can quite easily tell you why and how something works.

Also - Good luck to all of the people taking the AP test today!!

[Bakemaster]

If a student can't immediately recall that current is directly proportional to voltage and inversely proportional to resistance, I'd say they don't have a remotely adequate grasp of Ohm's Law. If the student is expected to understand anything about how a circuit works, they need to understand this fundamental principle. Would you claim to understand Newton II: Electric Boogaloo if you couldn't remember instantly if it was F=ma or Fa=m?

[KestrelLowing]

If a student can't immediately recall that current is directly proportional to voltage and inversely proportional to resistance, I'd say they don't have a remotely adequate grasp of Ohm's Law. If the student is expected to understand anything about how a circuit works, they need to understand this fundamental principle. Would you claim to understand Newton II: Electric Boogaloo if you couldn't remember instantly if it was F=ma or Fa=m?

Ok, V=IR was a bad example because it is so simplistic and almost everyone has that memorized. However, in more complicated equations, I think it's understandable. For example, let's take the Navier Stokes equation again.

Each term is easily explained and whether the term is positive or negative is pretty easy too. However, we're human! If we've got 40 other related fluids equations floating around our heads it would be really easy to forget a term, for example the f for other body forces as that often is ignored in many applications of the Navier Stokes. If I forgot a term of an equation and got a reasonable solution I think I would comfortably say that I still understand basic fluid dynamics but I just forgot the Navier Stokes equation.

[Windmill]

Yeah, I don't know most of these equations you all are talking about, especially the Physics equations, and I'm about to graduate with an engineering degree. If you get the general gist of classical mechanics, knowing specific formulas is kind of a waste of time and energy. Oh yeah, I forgot Coulomb's Law and Gauss's Law too. Ohhhhh well....

Real world: I can look it up in chart or book.

[Bakemaster]

Ok, V=IR was a bad example because it is so simplistic and almost everyone has that memorized. However, in more complicated equations, I think it's understandable. For example, let's take the Navier Stokes equation again.

I guess I should have been more specific: If you take issue with having to memorize formulas for your AP Physics test, you're definitely not ready to skip over the actual college physics coursework that corresponds to the AP Physics curriculum. I shouldn't have assumed that implication was obvious. The farthest the AP curriculum goes into fluid mechanics is very basic applications of Bernoulli's principle; Navier-Stokes is completely outside of its scope.

Sure, you can forget the laws and equations from your general physics series if you like—after you demonstrate competency by completing the coursework. The point I was trying to make is that if remembering them for the AP test is an issue, it's in your best interest not to be able to get full credit for the series at a school with a demanding curriculum.

[Wodashin]

What was up with the free response? I don't know if everyone in the country gets the same test, but holy crap. Multiple choice was significantly easier, which is different than most of the practice AP tests I've taken.

[Kirby]

Of course, we're not supposed to discuss the free response in specifics until Wednesday...

I will say, however, that on the EM test I came up with an answer I thought was right to all of the parts. Not so on the Mechanics free response.

The multiple choice actually had me worried for a little bit. I skipped a good half or so of the questions on my first pass through the test because I just couldn't remember enough of the specifics to come up with the answer. Miraculously, when I looked back over it, I could come up with an answer I was reasonably confident in.

Anyone else have thoughts on the exam?

[doogly]

I am a very strong proponent of memorizing your shit. Not as in, "let me sit down and memorize these things," but as in, "these fundamental equations are written in my heart." For intro mechanics, it has to work like this. If there was such a thing as understanding centripetal acceleration without knowing it is v^2/r, then it would be fine. But there is no such thing. I went through all of this logic with my class this semester on statistics, and the need to know formulas for standard deviation, normal distribution, so on. There are certain things you need to be intimately familiar with.

[KestrelLowing]

I am a very strong proponent of memorizing your shit. Not as in, "let me sit down and memorize these things," but as in, "these fundamental equations are written in my heart." For intro mechanics, it has to work like this. If there was such a thing as understanding centripetal acceleration without knowing it is v^2/r, then it would be fine. But there is no such thing. I went through all of this logic with my class this semester on statistics, and the need to know formulas for standard deviation, normal distribution, so on. There are certain things you need to be intimately familiar with.

Yes, but we're human and we easily forget things!! For example, standard deviation. You need to know what it represents but NO ONE calculates it by hand. Why do you need to know the formula when no one ever directly uses it? If you know what standard deviation is and why it's important, the specifics of how to calculate it aren't that important.

And yes, I believe there is a way of understanding centripetal acceleration without knowing it's v^2/r. The numbers don't really matter at that point, just the understanding that the acceleration points towards the inside of the curve, is related to velocity and radius, and the centripetal force is proportional to it.

[Bakemaster]

That's not enough of an understanding. You also have to know whether the relations are direct or inverse, and you have to know how radius and velocity are related. If you know these relationships, you necessarily have enough committed to memory to pull this particular equation out of thin air with very little effort and a high degree of confidence.

There are certain things you need to be intimately familiar with.

"That's where I come in," he continued with a wink.

[doogly]

Yes, in fact. I do that thing.

And I am not unmerciful. I will let factors of 2 slip. Anything that is pure dimensional analysis, like v^2/r, I think is fair game. If you put a 1/2 in front, my wrath would be tempered.

[KestrelLowing]

That's not enough of an understanding. You also have to know whether the relations are direct or inverse, and you have to know how radius and velocity are related. If you know these relationships, you necessarily have enough committed to memory to pull this particular equation out of thin air with very little effort and a high degree of confidence.

There are certain things you need to be intimately familiar with.

"That's where I come in," he continued with a wink.

Right, but if you know where to find the relation and it's readily available, why do you need to have it committed to memory!?! It's unrealistic to think that someone like a scientist or engineer will actually remember every equation they learn.

The way I think about it (please forgive me in advance - I'm not terribly skilled at programming) is that your memory should be full of pointers. You should know where to find the information you need. The actual information is not as important as knowing where to find it. Yes, this can slow you down and yes, things like F=ma are easily remembered. Obviously you also need to know how to apply said information.

Most people have an intuitive understanding of how mechanical things are related. So I don't need to look at a_c=v^2/r to know that if the radius is increased, the acceleration decreases. That's just instinct. No, I don't know by what factor, but that's what good equation sheets are for.

If working in another area like electricity, things may not be quite as intuitive at first but will quickly become so. Voltage increases when resistance increases. You don't technically need to know V=IR to understand that.

The human brain cannot flawlessly remember the majority of things so why should we force it to artificially? Eventually memorization will come if something is used enough, but why force it?

(It just occurred to me that we may be arguing approximately the same things. If so, I'm sorry)

[doogly]

Yeah, it probably is the same thing then. If you have done all of the homework, you can't *not* have v^2/r or f=ma memorized.

[Bakemaster]

Yeah, all that's required is to do what you said, Kestrel: Use the laws, equations and formulas over and over until you have them memorized. Still, for some people, flash cards and memory trickses make this easier when they just don't have time to work through thirty homework problems between Monday and Wednesday. Whether it's "artificial" or "forced" is really not important; the virtue is in knowing what you're supposed to know, however it is that you get there, and the same route doesn't work for everyone. No syllabus will work efficiently for every student, and I'd like to think the vast majority of decent teachers can recognize this. Homework is a super great tool for learning and pretty much everyone benefits; but some people do better by those means you dismiss as "forced" or "artificial" and there's nothing wrong with that. If someone needs flash cards or a mnemonic, then so be it; the class exists to give them a particular set of knowledge and skills, not to measure their ability relative to their circumstances.

What if you don't memorize the formulas? Well, no consequence is certain, but the less you know and the less automatically you know it, the more likely you are to make mistakes. The more likely you are to make any mistakes, the more likely you are to make significant mistakes. The real danger here isn't that you have to spend an extra few minutes thumbing through the index of your text or doing a search on Google. It's not even that you're stuck without any resources and have to remember this one formula in order to perform the impossible feat that will save both your girlfriend and your sidekick from certain death at the same time. It's simply that at some point, you'll think you know the formula and so you won't bother to verify it in a text or with a coworkers, but you'll be wrong. And yes, that can happen even when you had it perfectly memorized to begin with—but it's far less likely to! What's the consequence going to be? I dunno. Maybe you have to manufacture some extra beams and it costs your company a small amount of money. Maybe the error goes unnoticed and the orphanage collapses in a stiff wind, killing everyone inside. Probably something in between, but whatever it is, wouldn't it be nice to have to deal with these consequences less frequently?

[KestrelLowing]

Basically the problem for me personally is that I can't memorize formulas. I still don't have my multiplication tables memorized, and that's not from a lack of trying (seriously - flash cards, mnemonics, songs, everything). I just can't. My mind doesn't work that way. I'm horrible with vocabulary of foreign languages but the grammar is always really easy. I remember processes, I don't remember facts.

This usually results in me having to derive everything from the few equations I managed to memorize on tests when I am not allowed a formula sheet (thankfully few and far between now). I do the thing where I'll look at a formula right before a test, keep repeating it in my mind (I get VERY frustrated if anyone interrupts me before a test) and then when I get the test, write it down immediately because I can't just memorize it.

And I sincerely hope I'm never put in a life or death situation when trying to figure out whether the voltage increases or decreases when the current increases

[Bakemaster]

If I ever become a supervillain, keep in mind that I know your secret weakness now.

[gmalivuk]

The human brain cannot flawlessly remember the majority of things so why should we force it to artificially?

Because that's what education is. No one needs to teach you how to sit up or walk or speak the language(s) people use around you, because the human brain is very good at learning those things, pretty much flawlessly.

It's not so good, however, at learning to read or write or do math or logic or think in a systematic, scientific way. So that's what has to be taught artificially.

[freeeeeeeeeeeeeeeen]

All of my tests in all of my physics classes have had some sort of formula sheet, but if you don't know how to use the formula you're pretty screwed. And most of my tests in my engineering classes have either been open book, open notes or had a formula sheet. I agree it is more important to know how to manipulate the formulas than straight up memorizing them, but after using them often, its pretty hard to forget v=x/t or F=ma but no matter how much you try, it is nearly impossible and foolish to memorize some nonsensical empirical relation formula that things like engineering are full of.

[doogly]

Well, that's engineering. All the ones in physics make sense, so that helps.

[Rizzo]

I took this exam and I'll say I was not even close to being prepared.

My physics teacher wouldn't teach the subjects properly. But besides that, I highly doubt even getting a good grade on this exam would have helped in college. Why do I want to trust a high school taught course that is supposedly on a college level? The high school must think I'm to think that I even slightly know this. /rant

On another note, I liked how the exam at least showed the problems in a certain way. It was better than a typical plug-n-chug method on a regular test.

[Kurushimi]

This exam was interesting. The multiple choice and free response required more thought than I expected. It was much tougher than the previous exams we took. I really liked it. There was actually a problem I couldn't get.

[Kirby]

I will say that after working through various problems throughout the year, I didn't really need to use the formula sheet on the free response (it was provided on there). There were a couple formulas it would have been nice to know for the multiple choice, but (at least the ones I couldn't recall) I knew weren't on the formula sheet and could be derived, time permitting. Some hand-waving later, I was able to deduce the answer without too much trouble.

It's officially 48 hours after exam administration, therefore, we're now free to discuss the free response (note: we're never permitted to discuss the multiple choice in detail). If anyone's curious, CollegeBoard has posted the free responses on their website:
Physics B
Physics C: Mechanics
Physics C: E&M

I guess I'll be the first one to say it: what the hell was going on in 1.e/f in the Physics C Mech exam?

[Meem1029]

That is basically a conservation of momentum problem followed by a friction problem. I'm not sure how I would solve the second part off the top of my head (part f that is), but I think I'd be able to get it if I tried to. Note: This is coming from the perspective of a college freshman towards the top of his physics class at a top 5 for physics (as far as grad school attendance goes) liberal arts college.

[benoitowns]

This usually results in me having to derive everything

I would feel really bad for you if you ever encounter the derivative of natural log. That derivation takes soooo long

[mbrigdan]

I think he she means that he she has to rederive the more complicated formulas from the ones he already knows (eg: find half-life equation from the rate equation)*, rather than having to rederive that d (lnx) /dy = 1/x (and other such basic math knowledge).

*admittedly, this is chem, but I don't know enough physics for a real example

Edit: he -> she

[Bakemaster]

Also: she*

[KestrelLowing]

Yup! I'm a she.

And yes, that is what I meant. Some very simple, easy to memorize things I have down, but if I don't have a formula sheet I often have to derive more complex formulas.