# physics formulas and the mcat

Discussion in 'MCAT Discussions' started by JohnWetzel, Jul 12, 2011.

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1. ### JohnWetzelWikiPremed 7+ Year Member

297
31
Dec 29, 2008
Atlanta, Georgia
There are a lot of questions at SDN about how to look at physics formulas for the MCAT, which to commit to memory, which would be given on the test. There are a lot of posts and questions on how to view the conceptual versus quantitative problem solving nature of the MCAT. Being experienced in teaching a lot of folks for the MCAT I thought I would share my point of view.

The physics on the MCAT is conceptual. There aren't going to be that many plug and chug problems. However, the physics formulas that deal with the primary conceptual learning goals are the most compact way to see and understand conceptual physics. You should learn more formulas than these discussions suppose, to my mind, but you don't need to learn them in the way that many seem to be asking about. You don't need to have a lot of formulas in your memory to plug given information to find a number answer on many MCAT questions, but you do need more in your memory than many seem willing to believe. This is to understand MCAT physics. In a recent thread I posted a cart-load of formulas I think are critical http://forums.studentdoctor.net/showthread.php?t=303219 and wanted to clarify because if these were taken for plug and chug machines I may have misdirected some folks.

Actually there aren't that many formulas that really must be committed to memory for plug-and-chug problem solving, but if you are comfortable knowing and restating the seventy or eighty core physics formulas in plain English using real verbs, never saying equals, but imagining the simplest model system you can for the situation, you will a much easier time with the conceptual side of physics. Learning the formulas will save you a lot of time and confusion.

For example, direct proportionality is the common everyday language way of saying that a quantity increases in a straight line way with some other quantity. How far you go is directly proportional to how fast you are going and how long you travel. The height of a building is directly proportional to how many floors it has.

Try to use direct proportionality in a straightforward commonsense way in rephrasing physics formulas. The weight of an object is directly proportional to its mass. The work is directly proportional to the magnitude of the force in line with the displacement. The buoyant force is directly proportional to the weight of the fluid displaced. The kinetic energy is directly proportional to the square of the speed.

Wait. Instead of saying directly proportional to the square of the speed, you could say geometrically proportional to the speed itself. Knowing the formula in a conceptual way will help you navigate problems like the relative speeds of particles of two gases at the same temperature. Quadrupling the mass would have the same effect as doubling the speed on kinetic energy, so four times the mass would only need half the speed to have the same kinetic energy. Look at Graham's law for the effusion rate of gases and make your brain do this. Committing Graham's Law to memory because the AAMC expects you to plug in given information is not really the point. The process of thinking about what changes with what, what remains the same, and drawing conclusions is the heart of using physics formula to interpret phenomena as a kind of conceptual skill.

So there are common language ways of expressing exponential and geometric relationships, and you need to know how to do the inverse, as in the loudness is logarithmically proportional to the sound intensity. The MCAT passage would have the formula for decibels, but if your mind has never gone down the road of tackling the main formula, you won't be on track for the conceptual problems in the passage.

Some seem to be so extremely mathematically inclined, that the mathematical, formula expressions may be enough without messy language concepts, and there is almost a geometric kind of dynamic, imagination that is not really math and not really language, but many people, including myself, who is, if anything, blessed with the math thing do benefit in my physics by expressing the mathematical relationships in a plain language, conceptual way to myself, often simply using variation of proportionality, and I know it helps premedical students to do this.

Direct proportionality and inverse proportionality are just language tools to represent a situation where you can see one side of a physics identity, or equation, increasing or decreasing, respectively, because a quantity within is changing, and how it affects the other side. Try not to ever say 'equals' in restating a physics formula in common language and you will see how useful 'is directly proportional' or 'is inversely proportional' can be for understanding.

Inverse proportionality occurs mathematically expressed where you have two quantities multiplied by each other equaling some constant or where one quantity is in the denominator on one side and numerator on the other of the identity. The Reynolds number, which predicts when turbulent flow will occur, not an MCAT memory formula per se, but definitely a good one to know, is all else being equal, inversely proportional to the viscosity of the fluid and directly proportional to its density and speed. That's what I'm getting at. If you learn the formulas throughout physics as a conceptual language you will have already achieved most of the conceptual learning goals for MCAT physics which is about 'what changes with what' and 'what remains the same' through various simplified systematic ways of looking at the universe, that are so simple the relationships can be expressed with a formula.

Thought I'd share these insights because it keeps coming up. Sorry for the length of this post, but if you are reading this sentence, you made it through the thing.

Last edited: Jul 25, 2011
3. ### plzNOCarribbean

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May 21, 2010
Thanks for the insight John! I have to admit that I first started out with the heavy algebraic plug and chug mentality, but as I've been studying I am trying more and more to visualize the physical system. I do admit it does certainly help and is much more useful with regard to the conceptual questions, which seem to be the format of the recent MCAT's

4. ### macsta 2+ Year Member

471
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Jun 9, 2011
I agree with everything you said. But, learning the formulas is the easiest way (at least for me) to conceptualize topics. Also, there are some free standing questions that will ask you to plug-and-chug (i.e. what is the capacitance if you are given permittivity, area,and distance). I would just memorize the 40 or so equations given at the end of each chapter in review books. Memorize AND understand the equations.

5. ### Melomare17 2+ Year Member

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May 25, 2011
yes completely agree!

6. ### EnergyDrink 5+ Year Member

882
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Apr 3, 2011
I don't have any equations memorized. I have them all learned... but none memorized.

7. ### JohnWetzelWikiPremed 7+ Year Member

297
31
Dec 29, 2008
Atlanta, Georgia
I think a really helpful conceptual skill for physics is to picture a formula as an abstract ideal space in your imagination, where the events in a simple model system involve the changes described by the formula. Imagine a world where the only words allowed are the quantities in the formula, as simple and ideal as possible. Imagine a point mass in space with a constant force opposite its direction of motion. Let time pass. Imagine doubling the initial speed of the object and think about the same force now requiring four times as much distance to bring it to rest.

Everybody has their own tricks in teaching their minds how to learn different things. I think the most important thing is to understand the formulas as a way of seeing and predicting and making them interact with and represent the world in your mind like a language.

8. ### chemistryguy

Know how to do dimensional analysis. if a question gives choices that are all expressions with variables, you can simply solve many of them doing dimensional analysis!

9. ### liveoak

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Jan 21, 2011
just spend hours and hours, and everything will fall into place.

814
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May 25, 2011
yessss!

11. ### bambam02 5+ Year Member

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Jul 15, 2010
I wish there was a like button for threads on this forum like they have on facebook.

But anyway, i like what your saying

I feel like the MCAT just wants to make sure you understand how certain physical properties relate to others. Like you said, if you double the mass, you double the force.

This even applies to chemistry as well, most particularly to La' Chatlier's principle. They dont want to know how much salt is precipitated if you throw a common ion in the boil, they just want to know that salt does precipitate.

In the same light, they just want to know that you understand that if the earth was twice as massive, then the moon would be accelerating towards us twice as quickle.

12. ### TitusDoc

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Jul 18, 2011
Well said. I have been trying to figure out the best way to approach committing the physics formulas to memory for weeks now and think your explanation of visualizing them conceptually is really going to help. I'll work on this and take some Practice FLs and let you know! Thanks!