Since this is a four credit class, my expectation is that you will spend 6-8 hours outside of class working on physics. Since you do your laboratory writeups in the lab period, almost all of this time will be spent doing homework, working through posted homework solutions.

Not everyone learns in the same way. This means that not everything is going to work for everyone. We're trying a variety of techniques — to try and provide something to reach everyone. If there are some methods that work for you (and I don't mean that you enjoy doing — I mean that you feel help you get a better handle on the physics), focus on these at first. Don't cut the others off entirely! You may be surprised later on.

I do not believe that it is of much use for me to read the textbook to you in lecture. Instead, I will try to get you to think about the material in lecture -- to understand what it means, to organize it in your mind, and to see its implications. In a number of cases, the implications of thinking things through carefully will produce some startlingly unexpected results! These are of great importance and show you both the power of scientific reasoning and the danger of relying on an unrefined intuition.

My assumption is:

- that you will come to lecture
- that you will go to tutorial
- that you will do the homework
- that you will carefully go over the posted homework solutions and compare them to what you did
- that you will make some attempt to put all this info together for yourself into a coherent whole.

I will try to make the exams test the variety of skills we are trying to help you develop, so if you miss one of the three — readings, lecture, or discussion — regularly, you may find yourself unpleasantly surprised on an exam. If one of these three elements is not working for you, please come and see me and discuss the problem.

You may have learned to solve problems in high school or in other science courses by simple "pattern matching" — seeing a set of problems and copying them back on the exam from memory without understanding what is going on. THIS TECHNIQUE WON'T WORK HERE. It is essential to begin thinking about a problem by trying to imagine the real world situation it is describing. Then, you should decide what it is that is important in the problem and what is not relevant. (Sometimes you may have too much information, sometimes not enough.) Only then can you begin to set up the problem and think about what might be a relevant method or equation. Once you have solved the problem, you should evaluate your result for plausibility, again checking back to your real-world experience and understanding. Exam problems will include occasional traps to lead folks who pattern-match without thinking astray.

__You
should NOT expect to be able to look at a problem and see the answer
right away either for the homework or on an exam __. Problems where you
can see the answer right away are not really "problems" --
they are exercises. Most of the homework (AND some of the exam problems)
will be more complex than this. You should expect to have to "figure them
out".
To do this, it helps a lot to "know what tools you have to work with",
that is, to think about the physics we have learned, organize and classify
what you know, and be aware of how and when you can use it. The physics you
use should become a toolkit for solving problems with, not a simple one line
answer.

Furthermore, "simple pattern matching", that is, looking at a lot of problems and solving new problems by saying "oh, this is just like problem x" often won't work here as well. What we are doing is LEARNING TO SOLVE PROBLEMS BY REASONING FROM PRINCIPLES. This often requires multi-step thinking. Often, I will present a problem that looks superficially like a previously done problem but that has a critical change. If you are viewing the problem through surface features, you may well give the same answer as the previous problem, which will now be wrong. If you are viewing the problem through the principle you used to solve it and use the principle the same way you did in the first case, you will generate the new (and different) answer correctly and easily. This is part of the reason why in this class it is more effective to think a few problems through deeply instead of doing lots of problems superficially.

The exams will contain
a mix of problems: short answers, problem solving, explain in words, (one
to two page) essays, and estimation questions. The last are unusual but very
important. There will be one 15 point estimation question on every hour exam
(and one on every homework assignment). In these, you will have to make a
plausible guess at numerical information which is not given, and explain
why you made that guess. Your reasoning is what counts on these problems,
not the answer you get (within reasonable limits). This is also true for
problem solving: On an extended problem on an exam (not short answer) * little
or no credit is given for an answer for which no reasoning is shown.* Extensive
partial credit will be given for reasoning and explanations. (Even short
answer questions require explanations on homework.)
Note that an equation is not a reason. Almost no equation works in
every circumstance and those that (almost) do (at least for this course) require
analysis of what each term means. To get full credit on problems, you will
have to include at least a sentence or two explaining why you chose the equation
you did or how to apply it.

Calculators are permitted
on exams, but will rarely be needed. Any numbers to be calculated will be
requested to "one sig. fig. accuracy" and can be done
in your head. *Credit will be deducted for inappropriately many significant
figures and for misues of units.*

A card or sheet of equations will __not__ be permitted on the exams. Does
this mean you will have to memorize long lists of equations? No. Physics
is not a collection of equations. A very few need to be memorized -- and those
you __should__ know because they summarize fundamental conceptual knowledge!
Most of the others can be easily constructed correctly in a minute or two
if you understand where they come from and what their structure is. This
process will produce the correct result almost every time, whereas memorization
of a large number of equations has no "built in checks" so you often get
cross-links and wind up writing down the wrong equation. What I call "three-line
derivations" (TLDs)
are crucial for this course. They allow you to easily reconstruct dozens
of equations from a small number of fundamental principles.

One of the most important
problems with memorizing equations is that every equation has not only the
equation but its "context". Each equation has its
limitations. No equation works in all circumstances, so it is as important
to know the circumstances where an equation can be used productively and correctly
as it is to know the equation itself. Furthermore, an equation is not just
a way to calculate some quantity; it expresses a *relationship among physical
measurements.* This not only tells you how to calculate one quantity if
you know the rest, it tells you what other measurements must be kept fixed
for a change in one variable to produce an "obvious" in another,
and how changes in one quantity are associated with changes in another quantity
given that everything else is kept fixed. (For example, Δ*x* = <*v*>Δ*t* tells you
that a longer distance means a larger velocity -- but only if both objects
have traveled for the same amount of time.)

Problems from midsemester exams from previous semesters of this class will be posted on our website at Old Exams. This includes both the original and the makeup exams, and the makeup exams have solutions so you can see the kinds of answers I am looking for. Note, however, that each year, the materials covered for an exam (and in the course) tends to be slightly different.

Your TA should be your first line of defense when you are having trouble. Other resources include:

- your working group
- me or a TA in the course center
- the listserve
- the Slawsky clinic.

*To help you understand how to get information about the real world from experimen*t. In some of our labs you will be exploring situations that are more complicated than those discussed in lecture and text or will be done before we study them in lecture. You will have to figure out the result from measurements. This simulates how real scientific research is often done.*To help you understand how reliable your data is and what it tells you.*You will focus on this by thinking about how certain you are about the numerical values you obtain and by trying to convince the other groups in your lab that your data is correct.*To help you understand how to describe the relationships between measurements mathematically*. You will focus on this by proposing and testing mathematical functions to describe your results.

University of Maryland | Physics Department | Physics 121 Home |
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This page prepared by Edward F. Redish

Department of Physics

University of Maryland

College Park, MD 20742

Phone: (301) 405-6120

Email: redish@physics.umd.edu

Last revision 27. August, 2008.