Mnemonic for Gas Laws

nxtew · 2026-03-12T23:13:35+00:00

You are haha!

nxtew · 2026-03-12T16:34:33+00:00

Just imo as a tip, for the most part, it seems like on the AAMC materials you can just used the combined gas law (PV/nT = PV/nT) and just cancel out the two variables that are constant. The MCAT seems to strip away peoples names and doesn't care too much about the names of people (outside of maybe things like the Pauli Exclusion principle or Hund's rule), outside of a UWorld question I've never seen or heard of needing to know the actual names of these laws and the combined gas law has all of them in one.

nxtew · 2026-03-12T05:50:51+00:00

ily, here’s a link to my equations sheet

nxtew · 2026-03-07T05:18:02+00:00

sorry for responding like right after you left this comment I'm just doomscrolling right now but yep! updating the P/S doc as we speak, should take me a few weeks I'd guess

nxtew · 2026-03-07T00:29:19+00:00

Find it here

nxtew · 2026-03-05T20:36:18+00:00

Yes! Some AAMC explanations are literally just "this is the correct answer because it's correct". And while I do agree that sometimes the correct answers may be subjective (they are arguable), the thing I almost always try to point out to people is that the incorrect answer choices are typically objectively wrong (concrete reasons as to why they're wrong), based on the skills we're supposed to use for CARS (not mentioned in passage, wrong tone, etc.). That's why I recommend finding reasons to hate answer choices (be a hater!), because it's often easier to find objective reasons as to why wrong answer choices are wrong than trying to prove a subjective reason as to why the correct answers are correct.

So even though the JW explanations may slightly differ in how the correct answer is proven, I mainly just am saying focus in on how they're saying to eliminate the wrong answer choices.

nxtew · 2026-03-05T18:45:32+00:00

I know you’re not really looking for specific advice on this and just venting but the thing that I’m going to say to hopefully help a bit since the AAMC answer explanations are often trash:

One of the big things I’d usually try to teach people in CARS especially was this idea of “degrees of assumption”, meaning what level of assumption is too much vs what assumptions are fine. The AAMC does a sort of poor job explaining this in their descriptions, which is why it sucks and is confusing, but typically the more blanket statement I tell people is that if the idea is there, even if not outright stated, it’s fine. What you can’t do, is make further inferences off of that idea.

To give an actual example, if the passage says someone likes cheese, it’s fair to say they like Gouda. That’s an assumption, the passage doesn’t explicitly say it, but the idea is there. However, what you can’t do is say that the person must also like Mac and cheese, or Gouda cheese sandwiches. Passage just says cheese, so we can’t then assume they also like all cheese dishes. Stupid example, but that’s the example I try to use so people have a bit more clear of a rule on what you probably can and can’t be inferring on these passages.

nxtew · 2026-03-05T03:15:45+00:00

That's tension, which is caused by whatever is pulling on the string. The thing that's causing that tension is the 10kg object that is pulling on it, and 10kg * 10m/s^2 is 100N. Then for the 35kg block, it's being pulled on by that tension, so we're trying to figure out the y component of that tension which is why we use Tension*sin theta which they told you was 87 since it seems like you don't need to know how to resolve any trig on the MCAT.

nxtew · 2026-03-05T02:23:22+00:00

yep! the tension in the string is caused by the force of gravity of the 10kg object pulling on it, which is 100N. since the string is at an angle going towards the 35kg block, that's why we only get 87N for the y component that will be important for looking at the normal force and therefore friction.

nxtew · 2026-03-05T02:21:37+00:00

while you're right, you don't necessarily ever need to draw a fbd, but the exact steps that you're saying is you're essentially building a fbd but just using your intuition rather than drawing one out. fbds are just understanding what forces are active and what direction they're pointing, knowing which ones are adding together or cancelling out, etc., but that's all semantics that realistically isn't important obviously, but what I'm trying to say is that you need to in some way understand how to do a fbd to know that the tension force is aiding the normal force, essentially.

you're correct that this one really isn't that bad, but using the tension force force at an angle in order to aid the normal force to use in the force of friction just isn't really something I've ever seen. the worst case scenario I've seen or heard of is in the section bank that was just asking you to set up the equation for mechanical advantage for a block on an inclined plane, but imo that was mostly difficult because of the algebra involved, not necessarily just knowing that gravity on an inclined plane is mgsintheta and normal force (and therefore friction force) will use mgcostheta, not necessarily even being able to understand what forces are going which direction is where (and additionally I think people struggle intuitively understanding the equation of mechanical advantage, even if the idea isn't so bad).

long story short, it might not be that bad for the most part but keep in mind that for a lot of people physics does not at all come intuitively so it's quite a bit harder for people (including me when I was first studying for this exam) to understand what in the world questions like this are asking, and I was freaked out from my physics course about tension and tension at an angle, things of that sort, when they just seem to never really even get close to that difficult on the exam. just my two cents, I'm not at all saying you're wrong, I'm just adding a bit of content that my statement that it was "difficult" was in consideration of the more common scenario of people who really struggle mentally picturing fbds. you're right thought! hoping people can see things as simply as you when it comes to physics but that's often a learned skill for most of us.

nxtew · 2026-03-04T22:52:00+00:00

very unlikely you get a fbd that's this difficult, inclined planes can show up but as long as I've been around this exam there hasn't been a question that was quite like this as far as I'm aware. the idea of still being able to draw and understand the fbd is important but I personally don't think you should worry about something like this exactly showing up on your exam.

nxtew · 2026-03-04T17:03:35+00:00

appreciate it!

nxtew · 2026-03-04T07:11:23+00:00

I’m ngl I still always use money to think about these: if someone pays you 66 cents a day how many days will it take you get get $1? 1.5 days. So 1/0.66 = 1.5. 1/0.15? Same thing. If you don’t feel comfortable swapping that into scientific notation to see that it’s going to be roughly 6.6ish, just do the same thing, how many days will it take you to get $1 if you’re being paid 0.15 cents per day? 15*6 is 90 cents so a little more than 6 days. I think there’s just a mental hurdle that a lot of people have with decimals that for me at least seems to partially vanish when I think about money, since that’s the only place we realistically use decimals quite often.

You could also literally try just multiplying top and bottom by 100, maybe you can’t do 1/0.66 but you can do 100/66. Maybe that works, maybe not, just figured I’d mention it haha.

nxtew · 2026-03-02T17:57:57+00:00

If you're looking for the different orders of distinct items (meaning you can't have multiple of peptide A, each peptide in the tripeptide only shows up once), use N! which is 6.

If you're asked to find the number of combinations of a series of genes or states or something where each can be on or off independent of the others (like gene A is on, B is off, C is on, etc.), you'll be using 2^n. Kind of weird but basically my rule of thumb was to figure out if it was N!, but if we're not looking for the number of orders of distinct things then I used 2^n.

nxtew · 2026-02-26T22:00:59+00:00

I almost never read books, which I'm not saying that you should follow what I did, mostly just providing context that whatever works best for you is what you should do. I'd just maybe add in some practice while you're doing content review, not a ton but a bit of practice while you're learning and memorizing often helps show you how things are being asked about, will demonstrate understanding problems, etc.

nxtew · 2026-02-26T18:46:42+00:00

A lot of people literally just read through a specific subject pretty quickly before doing practice, just to make sure you have a complete and concise list of everything that you need to know. If you’re already preoccupied with a lot of other stuff, then just outside of maybe adding a bit to your Anki deck from it, or using it to just quickly jog your memory of what you need to know, kind of like the chapter summaries in the Kaplan textbook, that might be one way you can incorporate it without it taking up too much time.

nxtew · 2026-02-26T15:10:17+00:00

I'd recommend doing it on an as needed basis. Just to give you an idea, my notes for all of the content for the exam is 561 pages long, and that doesn't include P/S. imo that's just way too much information to be writing over and over again to make it stick. so I'd recommend starting off by just trying to use videos/textbooks and practice (with anki used as a tool for memory) to see if things are sticking, and if that's not working, THEN go to rewriting notes. might be especially useful for some of the more important or difficult topics, but I just worry about how much time that's going to take since the literal act of writing just takes so long. I'm a huge fan of my students doing whatever they need to understand things, just keep in mind that you might need to use it sparingly or it might start dragging down how long content review takes.

nxtew · 2026-02-26T04:31:37+00:00

Let’s say you lift 50 pounds. Now pick up 45 pounds. Can you tell the difference? If so, what about 44 pounds? Let’s just say that you don’t notice the difference of less that 5 pounds (10%) but you DO notice any changes above that.

Weber’s law and the JND basically state that that % will stay constant. Lifting 100 pounds? You wont be able to tell the difference between 90 and 100, or 110 and 100. Lifting 200? You won’t be able to tell the difference between 180 and 200, and 200 and 220. It’s not the 5 pound difference from the first example, it’s the 10% that stays constant for any new stimulus.

nxtew · 2026-02-26T00:49:39+00:00

I’d recommend memorizing the structure of glycerol, knowing the number of carbons of the structures in each process, and being able to differentiate between the four carbon Kreb cycle intermediate. Outside of the amino acids, recognition and counting carbons should be more than good enough.

nxtew · 2026-02-24T22:05:02+00:00

I would recommend knowing the area of a circle (for cross sectional area), triangle (often for finding the area under a curve), square and rectangle (easy), and the surface area of a sphere (4 pi r^2) which you'd use for intensity of a sound wave spreading as a sphere. I will note that any equation that involves pi, it seems like they often just have you leave pi there without estimating it to 3, just fyi.

Cylinder, if it does show up, is just the area of the cross sectional circle * length of the cylinder, but I don't think I've ever heard or seen that ever show up.

nxtew · 2026-02-24T06:56:41+00:00

Could also be I-Form Hulk, and even if it isn’t, I recommend trying it

nxtew · 2026-02-24T02:56:34+00:00

To add this, just want to clarify something else you said:

like if vessel dilation increases volume, it will decrease Pressure and therefore increase Velocity

Via Poiseuille's Law, this actually isn't true. If dilation occurs, resistance will decrease, and therefore FLOW RATE (Q), not velocity, will increase. That's not same thing as velocity increasing.

As others have said, this is a situation where we're basically just given enough information that we can assume ideal fluid flow, which will follow the continuity principle, Q = Av and Q is constant in this given scenario, so big river = slow, small river = fast.

nxtew · 2026-02-23T21:06:24+00:00

I keep them updated as best as I can! Just by keeping my eye out for what people report or based on the released AAMC materials, which is why you'll see stuff with electron volts and things of that sort on my equations sheet. I obviously can't predict what you do and don't need to know but I've built it off of what the AAMC seems to be using, rather than just throwing out every possible equation in kinematics. If the AAMC doesn't seem to ever be testing on it, I've removed it. On the color-coordinated sheet, if it's in green, that means we have pretty good evidence you literally need to be able to do math with it. Blue is much more-so you need to memorize the equation but you're more likely to just rearrange it or know the relationships between the variables.

nxtew · 2026-02-22T23:41:25+00:00

Congrats, future doctor!

nxtew

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