Discussion of Course Goals

Explanation of some of the unusual features of the class

My goals for this class

My goal for this class is to get as many of you as possible to understand both the content of physics and learn how to think about physical situations scientifically.

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.

Text vs. Lectures vs. Discussions

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:

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.

Problem solving

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 Course Center

Room Toll 0208 is set up in a way for you to be able to have a place to work on physics problems. There will be a variety of texts available, plus tables and whiteboards. This is a good place for groups to meet to discuss the homework. Helpers (TAs or me) will be available to answer questions or make suggestions in the course center at the times listed on the "Times" webpage.


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, Δx = <vt 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.

Powers of 10 (scientific notation) and units

In many of your previous science and math classes you have been taught to use scientific (powers of 10) notation and how to attach units to measurements. But often these were not required and in my experience many students in this course are still not comfortable with these methods. The buck stops here. You will be required to use both scientific notation and units. Answers without units will be simply considered wrong (they are) even if the numbers are correct. Answers that are correct but not in scientific notation (such as 1,373,682 instead of 1.4 x 106) will lose a point for too many significant figures and a point for not being in scientific notation. If you are not comfortable with scientific notation, now is the time to figure it out! (It's actually quite simple if you can add and subtract one and two digit numbers in your head -- which you also ought to be able to do.)

Having trouble?

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

What's with the labs?

The labs for traditional physics classes have as their primary goals to familiarize you with handling lab equipment and to demonstrate the real-world correctness of results presented in lecture and in the text. This provides little introduction to realistic scientific laboratory procedures that require you to develop insight and creativity. We therefore replace the traditional labs by ones in which you will be given a task and some equipment and will have to find ways to come up with the results yourselves. The laboratory period will be structured to help you to do this and you will be able to get (and provide) assistance from other members of the class and from your TA. This lab should be considerably more intellectually challenging than traditional protocol labs. The lab has three primary goals.
  1. To help you understand how to get information about the real world from experiment. 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.
  2. 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.
  3. 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.
See A Guide to the Laboratory for more details.


University of Maryland Physics Department Physics 121 Home

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.