Memorizing Equations in the Shower for AP Physics B & C

Treat Equations Like Vocabulary

Think about how you would memorize a vocabulary word: for example, "boondoggle." There are several ways to memorize this word. The first way is to say the word out loud and then spell it: "Boondoggle: B-O-O-N-D-O-G-G-L-E." The second way is to say the word and then say its definition: "Boondoggle: An unproductive or impractical project, often involving graft." If you were to use the first method of memorizing our word, you would become a great speller, but you would have no clue what "boondoggle" means. As long as you are not preparing for a spelling bee, it seems that the second method is the better one.

This judgment may appear obvious. Who ever learned vocabulary by spelling it? The fact is, this is the method most people use when studying equations.

Let's take a simple equation, v_f = v_o at. An average physics student will memorize this equation by saying it aloud several times, and that's it. All this student has done is "spelled" the equation.

But you're not average.¹ Instead, you look at the equation as a whole, pronouncing it like a sentence: "V f equals v naught plus at." You then memorize what it means and when to use it: "This equation relates initial velocity with final velocity. It is valid only when acceleration is constant." If you are really motivated, you will also try to develop some intuitive sense of why the equation works. "Of course," you say, "this makes perfect sense! Acceleration is just the change in velocity divided by the change in time. If acceleration is multiplied by the change in time, then all that's left is the change in velocity

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So the final velocity of an object equals its initial velocity plus the change in velocity."

The first step in memorizing equations, then, is to learn them as if you were studying for a vocabulary test, and not as if you were studying for a spelling bee.

Helpful Tips

Memorizing equations takes a lot of time, so you cannot plan on studying your equations the night before the AP exam. If you want to really know your equations like the back of your hand, you will have to spend months practicing. But it's really not that bad. Here are four tips to help you out.

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Just as with vocabulary words, you will only learn physics equations if you use them on a regular basis. The more you use your equations, the more comfortable you will be with them, and that comfort level will help you on the AP test.

The reason you should try solving homework problems without looking up equations is that this will alert you to trouble spots. When you can look at an equations sheet, it's easy to fool yourself into a false sense of confidence: "Oh, yeah, I knew that spring potential energy is ½ kx²." But when you don't have an equations sheet to look at, you realize that either you know an equation or you don't. So if you solve homework problems without looking up equations, you'll quickly figure out which ones you know and which you don't; and then you can focus your studying on those equations that need more review.

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Use whatever tricks necessary to learn an equation. For example, it is often hard to remember that the period of a pendulum is

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and not

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So make up some trick, like "The terms go in backward alphabetical order: Two-pi root L over g." Be creative.

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Practice speed. Say the equations as fast as you can, then say them faster. Start at the top of the AP equations sheet² and work your way down. Have someone quiz you. Let that person give you a lead, like "Period of a pendulum," and you respond "Two-pi root L over g." See how many equations you can rattle off in four minutes. We call it the 4-Minute Drill.

This is much more fun with a group; for example, try to persuade your teacher to lead the class in a 4-minute drill. Not only will you get out of four minutes of lecture, but you may also be able to bargain with your teacher: "Sir, if we can rattle off 50 equations in the 4-Minute Drill, will you exempt us from doing tonight's problems?"³

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See how the equations sheet looks next to your bathroom mirror. Or in your shower (laminated, of course). Or taped to your door. Or hung from your ceiling. You'd be surprised how much sparkle it can add to your décor. You'd also be surprised how easy it will be to memorize equations if you are constantly looking at the equations sheet.

So what are you waiting for? Start memorizing!

Answer Key to Practice Quiz

1. 
2. p = mv
3. I = Δp
4. I = FΔt
5. P = Fv
6. 
7. 
8. V = IR
9. W = Fd
10. W = ΔKE
11. n₁ sinθ₁ = n₂ sinθ₂
12. P = IV
13. T =
14. F_net = ma
15. 
16. 
17. 
18. ½mv²
19. 
20.