The other tool you can use on the free-response section is the equations sheet. You will be given a
copy of this sheet in your exam booklet. It’s a handy reference because it lists all the equations that you’re
expected to know for the exam.
However, the equations sheet can also be dangerous. Too often, students interpret the equations sheet
as an invitation to stop thinking: “Hey, they tell me everything I need to know, so I can just plug-and-chug
through the rest of the exam!” Nothing could be further from the truth.
First of all, you’ve already memorized the equations on the sheet. It might be reassuring to look up an
equation during the AP exam, just to make sure that you’ve remembered it correctly. And maybe you’ve
forgotten a particular equation, but seeing it on the sheet will jog your memory. This is exactly what the
equations sheet is for, and in this sense, it’s pretty nice to have around. But beware of the following:
• Don’t look up an equation unless you know exactly what you’re looking for. It might sound obvious, but
if you don’t know what you’re looking for, you won’t find it.
• Don’t go fishing. If part of a free-response question asks you to find an object’s momentum, and you’re
not sure how to do that, don’t just rush to the equations sheet and search for every equation with a “P ”
in it.
Math and the Physics C Exam
Physics C students often worry about the math they’re expected to know for the AP exam, because some of
the material covered in the Physics C curriculum involves pretty complicated calculus. Maxwell’s
equations, for example, involve concepts that are well beyond the scope of most high school calculus
classes.
Whether or not you are carrying an A in your AP Calculus course is irrelevant. Most importantly, you
must have a strong understanding of the physical meaning behind the mathematics. The problems that
might seem to involve calculus—those that use an integral or derivative equation from the equations sheet
—can often be approached with algebraic methods. Remember, an integral is just the area under a graph;
a derivative is just the slope of a graph. If you have to, set up an integral and don’t solve it. Or explain in
words what your answer should look like. Also, note that many of the equations that appear on the
equations sheet as calculus expressions rarely or never need calculus. For instance, Gauss’s law has a
nasty integral in it, but when used correctly, Gauss’s law rarely requires any calculus. Whatever you do, it
is not worth the time and frustration to focus exclusively on the tough calculus—this isn’t a math exam,
and the point distribution in the rubrics reflects this fact.
Other Advice About the Free-Response Section
• Always show your work. If you use the correct equation to solve a problem but you plug in the wrong
numbers, you will probably get partial credit, but if you just write down an incorrect answer, you will
definitely get no partial credit.
• If you don’t know precisely how to solve a problem, simply explain your thinking process to the
grader. If a problem asks you to find the centripetal acceleration of a satellite orbiting a planet, for
example, and you don’t know what equations to use, you might write something like this: “The
centripetal force points toward the center of the satellite’s orbit, and this force is due to gravity. If I
knew the centripetal force, I could then calculate the centripetal acceleration using Newton’s second
law.” This answer might earn you several points, even though you didn’t do a single calculation.
• However, don’t write a book. Keep your answers succinct.
• Let’s say that part (b) of a question requires you to use a value calculated in part (a). You didn’t know
how to solve part (a), but you know how to solve part (b). What should you do? We can suggest two