AP Physics C 2017

Physics is  NOT about   numbers.

Yes, you must use numbers occasionally. Yet you must understand that the number you get in answer to a
question is always subordinate to what that number represents.
Many misconceptions about physics start in math class. There, your teacher shows you how to do a
type of problem, then you do several variations of that same problem for homework. The answer to one of
these problems might be 30,000,000, another 16.5. It doesn’t matter ... in fact, the book (or your teacher)
probably made up random numbers to go into the problem to begin with. The “problem” consists of
manipulating these random numbers a certain way to get a certain answer.
In physics, though, every number has meaning . Your answer will not be 30,000,000; the answer may
be 30,000,000 electron-volts, or 30,000,000 seconds, but not just 30,000,000. If you don’t see the
difference, you’re missing the fundamental point of physics.
We use numbers to represent REAL goings on in nature. 30,000,000 eV (or, 30 MeV) is an energy; this
could represent the energy of a particle in a multibillion-dollar accelerator, but it’s much too small to be
the energy of a ball dropped off of a building. 30,000,000 seconds is a time; not a few hours or a few
centuries, but about one year. These two “30,000,000” responses mean entirely different things. If you
simply give a number as an answer, you’re doing a math problem. It is only when you can explain the
meaning of any result that you may truly claim to understand physics.

So How Do I Deal with All the Numbers on the Test?

You see, in virtually all cases the test authors still assume that you have no calculator. Thus, a large
majority of the multiple-choice questions involve no numbers at all! And those questions that do use
numbers will never require more than the simplest manipulations. Here is a question you will never see
on the AP test:

What    is  the magnitude   of  the magnetic    field   a   distance    of  1.5 m   away    from    a   long,   straight    wire    that

carries 2.3 A   of  current?

(A)     3.066   ×   10–6 T

(B)     3.166   ×   10–6 T

(C)     3.102   ×   10–6 T

(D)     2.995   ×   10–6 T

(E)     3.109   ×   10–6 T

Yes, we know you might have seen this type of problem in class. But it will not be on the AP exam. Why
not? Plugging numbers into a calculator is not a skill being tested by this examination. (You should have
recognized that the equation necessary to solve this problem is