Monday-Wednesday (CORE)/Friday (AP)

1:00p - 2:30p ET/10:00a - 11:30a PT

Student Guide

Or:

How to survive a science course, with special attention to the problems of studying physics

- Why Study Science?
- The Science Course
- Managing Your Time
- Web Lectures
- Getting to Know the Textbook
- Doing Homework
- Getting the Most from Chat
- Quizzes
- Exams
- Study Groups
- Doing Labs
- Writing Lab Reports
- Resources

At the heart of all science is something called * the scientific method*. The simple version of the scientific method is based on the idea that the objective reality of the universe can be determined by carefully observing phenomena, recording appropriate measurements, then studying the data from these observations for patterns that can be used to describe the general behavior of classes of natural objects. When we can control the circumstances of the observations, we are performing

Many physics events are * periodic*, that is, they happen over and over again, in the same way, at the same speed or time interval. Heavier items consistently make a deeper dent in the earth when they hit the surface. Some metals, in chips small enough to float on water, will spin round and orient themselves toward the Pole Star. Water, when it turns to steam, expands to fill more speace (it also expands when it turns to ice!).

When scientists find similarities between objects, or patterns of behavior that repeat with little variation, they want to study the similarities to see if there is some common cause behind them. When the scientist finds a reasonable explanation, he or she proposes a *hypothesis*, a testable statement about the phenomena. Hypotheses that stand up over many repeated observations are combined to make *theories*; distillations of theories that have no known exceptions may be called *natural* *laws*. In physics, we are particularly concerned with motion (kinematics), forces (dynamics), energy and heat (thermodynamics), and how these apply to the very small objects inside the atom (quantum mechanics) and very large areas of space (relativity and cosmology).

Science classes are frightening for many students. They anticipate difficulties with the concepts, with the details, and especially with the math. But science is just one way of thinking about the natural world around us, and anyone can learn to think like a scientist. Don't waste energy worrying about your ability to learn the material; use your energy to learn it! Once you get the hang of it, you'll be able to discover, understand, and appreciate the complexity of God's creation better. You will also be better prepared to take your place as a steward of that creation.

Review the prerequisites for the course. These are the concepts and math skills that you should have mastered in order to succeed in learning the material. The math prerequisites for this course are described in the course overview page and the FAQs page. If you have any questions about your readiness for the course, be sure to ask for help during our first session. I will arrange to work with you so that you can gain the required skills quickly.

Every science course has as its main components lectures, reading assignments, labs, and lots of homework to prepare you for taking quizzes and exams. In addition to these, our online course has this website, the Moodle, and e-mail to provide the functions that would normally exist in talking to your teacher face-to-face, or looking at a bulletin board or whiteboard. Keeping track of all the components can be a daunting task, especially at first, so plan to spend some time becoming familiar with the course website, your text, and the Moodle. Once you have mastered the mechanics of using these tools, you can concentrate on learning the material that they contain.

Why are there so many parts to the course? Well, part of the reason is that you learn in many ways. You memorize facts, you comprehend relationships, and eventually, you understand concepts. You learn by reading, by analyzing pictures and graphs, by watching demonstrations of processes, by participating in discussions, and by applying what you are learning to specific situations in the homework and labs. You "cement" what you've learned by teaching others. The organization and materials of the course require that you take all these approaches.

Make the commitment, now, to spend adequate time on coursework. This course will challenge you mathematically as well as conceptually, so you must realize right from the start that you cannot do all the work for a given unit on one day ... and you shouldn't do it just before chat session! The table below is a rough guide and a suggested pace for this course. The amount of time you spend on each part of the assigned work will vary greatly from student to student, and your schedule will of course depend on your other commitments. Work out a reasonable work load and stick to it!

Try to do your reading as early as possible. This allows you to think about the questions and material, review it in your mind, and absorb it more critically.

**Checklist and schedule**

Completed? | Task | Approximate Time | Scheduled for... | |

1 | _____ | Check Moodle for instructions for next chat session | 15 minutes | Immediately after each class session |

2 | _____ | Read Next Web Lecture | 1/2-1 hour | Monday/Wednesday after chat |

3 | _____ | Read Text Assignment (and work through example problems or questions!) | 1-2 hours | Monday/Wednesday after chat |

4 | _____ | Work through plantarium exercises [Astro], watch videos [Chem], perform Lessons (if any) or simulations [Phys] | 1-2 hour | Tuesday/Thursday |

5 | _____ | Complete Mastery Exercises | 1-2 hours | Tuesday/Thursday (Sat) |

6 | _____ | Complete individual problem and post solution to Moodle | 1/2 hour | Before chat when due |

7 | _____ | Complete AP example (AP option students only) | 1-2 hours |
Thursday (due Friday) |

8 | _____ | Attend Chat and ASK QUESTIONS |
1.5 hours |
Chat Schedule |

8 | _____ | Plan and perform for lab |
1-2 hours |
Tues |

9 | _____ | Perform calculations/reduce data |
1 hour |
Two days before lab due |

10 | _____ | Write lab report |
1 hour |
Day before lab due |

11 | _____ | Take Moodle quiz | 20-30 minutes | (only at the end of the chapter) |

Rather than take our precious chat time by lecturing to you, all unit lectures are posted to the site. You need to read these as well as the text. The Homework and Weblecture pages between them have

- study guide notes to help you with the reading
- a lecture that expands on the text or go into details about related topics
- practice with concepts (checkpoints for your understanding)
- lists of discussion questions to prepare for chat
- application examples or process analysis
- highly recommended website simulations or videos on specific topics
- link to the associated lab

The "checkpoint" exercises ask you to figure something out, then offer you the opportunity to check your answer. Try to figure things out before hitting the "answer" button! If you were correct, and your reasoning was correct, congratulations! You are ready to continue with the next concept. If you missed the answer, but understand the correction, make a note to review the concept later. If you don't understand the explanation, ask the teacher during class, or send e-mail requesting further help.

As you read the web lecture, make notes on anything that puzzles you, and be sure to raise your questions in class.

Examine your copy of *Physics: Principles with Applications* (Giancoli, ed. 7) as soon as it arrives. Read through the *Notes to Students and Instructors on the format* on the use of color and symbols in the diagrams, so that you can easily deterimine whether you are looking at a force or field vector. Study the table of contents: each chapter builds on concepts in the previous sections, so we cannot study electrical field theory until we understand how forces work.

Examine the endpapers inside the front and back cover, so that you know where to find important constants and unit conversions. You will use these in many exercises throughout the year. You may even want to photocopy these so that you can refer to the information easily without having to flip back and forth while working a problem.

Check the appendices in the back of the book, especially the mathematical review in appendix A. If there are any new concepts you have not already covered in your mathematics curriculum, be sure to bring these to the instructor\s attention during the first chat session, so that we can go over them.

As you plan your reading, be sure that you give yourself enough time to

- review some of the previous material, such as the key idea summary at the end of the last chapter
- read through new material carefully and thoughtfully
- TAKE NOTES! Outline the section you are reading, identify important terms, concepts, and formulae.
- study the diagrams; some are "just for pretty", but most are integral to the presentation of material
- test your understanding of the section by answering one or more of the questions at the end of the section and checking your answer against the answer in the back of the book (the "AITBOTB").
- after each section, write down the important points it makes, any items of particular interest, and any questions that you have.
- check the vocabulary lists at the end of the chapter

For any calculation examples in the text, make sure that you understand

- how to interpret the example questions, so that you know what you are looking for
- how to identify the equation or method to solve the problem
- how to map the information in the question to variables in the equation
- when to convert units, and why
- how to perform the mathematical techniques involved and get a numerically correct answer
- how to figure out the significant figures for the answer

Homework is not merely useful, it is *essential* for mastering the concepts of any science course. Just as we test theories by applying them to experimental situations, you test your understanding by applying it to specific situations. You will know whether you understand a concept if you can use it to solve a "real-world" problem, and when you can teach it to someone else.

You will be assigned word-essay questions, observational data analysis, and calculation problems for each unit as part of a forum, mastery exercise, or lesson found in the Moodle section for the week. Moodle lessons may present new information not covered in detail in your text, and test your comprehension of this material. Mastery exercises will test your understanding of terminology and your ability to distinguish closely related concepts and apply them correctly to examples. You may be asked to identify components of a system by matching terminology, labelling diagrams, or completing a crossword-puzzle challenge. Some examples will ask you to perform basic tasks several times in different ways to make sure that you understand how to apply them. You may be led step-by-step through a complex calculation, then asked to calculate a similar example on your own. Follow any directions to express your answer in a particular format so that it will be correctly scored! Study exercise feedback even if you got the right answer, so that you can use the method or information in other situations.

You will also be asked to post the answer for at least one question or essay topic to a Moodle forum shared by your fellow students for discussion. If the question involves calculation, you will need to show your calculations and explain them in your posted answer. This is your opportunity to explain to your fellow students what you know — to teach the idea to someone else.

Your reading assignment will be on both the Moodle and the Schedule page, along with links to my Web lecture and study notes for the assignment. You are expected to do any online exercises, watch any videos, and complete any tutorials assoicated with the reading that are assigned in the homework page or weblecture. Questions based on this material may be included in your mastery exercises, individually-assigned problems, or quizzes.

NB: mycroft, the original bot for my science classes, has long since been freed to do other things, like attend class, make obnoxious remarks, and aid stumped students. If you really get stuck figuring out the problem you've been asked to post, mycroft has been known to accept bribes in the form of virtual Oreo cookies to finish your problem for you.

Essay questions ask you to explain a concept in words. As you answer a science essay question, be prepared to cite calculation information as well as concepts, or give examples.

Here is an example:
**At which point is its path does a projectile have the least vertical speed?**

A good answer will be grammatically and syntactically correct, using proper English, as well as contain the correct information. It will cover more than one point in supporting its argument.

Most physics concepts are really simple. The relationship of velocity, distance, and acceleration can be expressed as

v^{2}= v_{0}^{2}+ 2a(x - x_{0})

which is relatively simple math. Our problem is in the application of such concepts to real situations.

So here is a "general problem solving" approach.

- Visualize the situation described. Make sure that you understand what is happening in the real or idealized physical event.
- Identify and list all known values given in the problem and the unknown to be found.
- If appropriate, chose a coordinate system that simplifies the math.
- Determine whether or not the units should be converted, and complete the conversion (e.g., one value is listed in grams, but your constant is in kilograms).
- Set up a notation system for the knowns and unknowns, so that you can use the symbols in math relationships.
- Check for any hidden information — values that you know because of the situation, but which may not be explicitly given in the description. For example, starting velocities for "falling" objects (not thrown) are assumed to be zero.
- Look for a relationship that relates what you know to what you don't know. You need one equation per unknown value.
- Solve the formula for the unknown. Don't substitute values in prematurely: you'll only wind up doing more math. Make sure that your units will cancel to give you the correct units for the answer. For example, if you set up a formula to find distance, and the units of the knowns cancel to sec
^{-1}, you've done something wrong. - Once you have the final version of the formula isolating the unknown and setting it equal to known values, substitute the known values into place.
- Do the arithmetic.
- Check your answer for reasonableness, direction, and proper units.

Let's look at an example:

*In coming to a stop, a car leaves skid marks 80m on the highway. Assuming a deceleration of 7.00 m/s ^{2}, estimate the speed of the car just before braking.*

**Visualize the situation described.**Be sure that you understand the concepts involved before you think about how they relate to a mathematical description. Here, visualize what is happening: at some point in time, the driver applies brakes. The car travels 80 meters before it stops. It is decelerating at a constant rate (it doesn't "slow down faster and faster" but slows down steadily).-
**Identify all the "knowns" and the "unknowns".**Here we have distance (80m) and deceleration (7.00m/s^{2}). Identify what you want to find out: here it is the speed of the car just before breaking, which will be the magnitude of the velocity at the start of the event. So I am looking for v_{0}. **Select a coordinate system**. You have vectors, which means direction is important. You must figure out where you are measuring from (an origin point), and how you will measure direction, velocity and acceleration from it. You can set this up any way you like, as long as you are consistent.to simplify the math. For example, you could pick some street corner six blocks away to measure the start and finish displacements from...but then you have to mess around with extra values. It is better to chose the start or end of the deceleration itself -- and useful to note that it doesn't matter which as long as you are consistent through the problem. Since I think of braking the car as a process, I chose the start of the braking as the zero position from which I measure distance.**Set up a notation system and list your values.**Translate the knowns into mathematical quantities. Here if I decide to measure from the start of the braking, x_{0}= 0 and x = 80m. If I measure in the direction of travel (velocity is positive going from x_{0}to x), then**de**celeration is in the opposite direction, and the acceleration factor a is -7.00m/s^{2}. My list: x_{0}, x, v_{0}, a, and we want to find v.**Check for any "hidden" information that isn't explicitly stated**. The problem says the car stops, so its final velocity v = 0.**Look for a formula that relates most of these together**. Of the list on p. 28, the one that only uses factors we know isv

^{2}= v_{0}^{2}+ 2a(x-x_{0})**Isolate the value you want to solve by solving the formula**. In this case, we want v_{0}, so we have to rearrange isolate that factor on one side of the equal sign:v

^{2}- 2a(x-x_{0}) = v_{0}^{2}and then take the square root to get v

_{0}:√ (v

^{2}- 2a(x-x_{0}) ) = v_{0}**Substitute the numbers into place**:√ (0 - 2*(-7.00m/s

^{2})(80m -0) ) = v_{0}**Solve for the arithmetic answer**:√ ( -2 * -7.00m/s

^{2}* 80m ) = √ (14 * 80 m^{2}/s^{2}) = √ (1120m^{2}/s^{2}) = 33 m/s**Double check your work**for magnitudes, direction (in the case of vectors) and units.- Your answer is in terms of dozens of meters, which is consistent the with order of magnitude of the length of the skid marks and the deceleration rate. If you had gotten values of .001 meter or 10000 meters, you would definitely want to redo your calculations.
- Velocity is positive, acceleration was negative. This is consistent with a deceleration situation.
- You were looking for velocity, which is in units of distance/time. m/s is distance/time, so the units work out properly.

During our weekly meeting, we will base our discussion on the material in our textbook. We will also discuss demonstrations found on the web or in our Moodle, websites of related interest, homework problems, and any observations that you make during the week.

If you come to chat without any questions, you aren't paying enough attention to the material!

You may raise questions about the material from the text, my web lectures, your homework, your labs, and when we have time, from news media articles with a physics connection, such as the discovery of gravity waves, the detection of new subatomic particles, or the implications of entanglement in quantum mechanics. I realize that there are diverging scientific, philosophical, and theological opinions on much of the material that we cover, particularly on the origin of the universe.

You may challenge any statement made in class or in your text, as long as you do so politely. You do not have to agree with all of the tenets proposed by your textbook authors, your teacher, or your fellow classmates, but you should be able to clearly state their arguments in terms they would accept, and address your concerns to those positions. Act with respect to each proponent and assume that each is trying to make the best sense of the universe.

I do consider your contributions to our discussion in determining your final grade and making comments, so don't just sit back and watch others type. If you have questions, ask them! When you are assigned a report topic or a homework problem to post, be sure that you have spent adequate time to prepare not only the formal content that you post to the class forum in the Moodle, but also to anticipate the questions of your fellow students about your topic.

Chat sessions are 90 minutes. Plan accordingly, and take a break just before class starts. Do some stretching, go to the bathroom, eat or get your drinks before you enter the classroom. Be sure to try to connect to your ISP and check mail 10 minutes before class if possible, in case any late notices have been sent by the teacher. Give yourself the extra time. High traffic on your ISP or the school server can slow you down and force you to miss the first 5 to 10 minutes of class.

If you have not already done so, post any pre-chat preparation materials, including essays and individually-assigned problems, to the Moodle before chat.

**Bring your textbook, notes, homework calculations, calculator, and paper and pencil to class**. If you are comfortable using a desktop calculator and taking notes in a text utility like Notepad (available as different applications on both Windows and Macintosh), you can use those. You may also find a dictation program like Dragon helps reduce typing, either into chat or taking notes. Take notes during class. Since Scholars Online logs the chat sessions, you do not need to document things the teacher or other students say, but it is useful to note your own questions and observations as they occur, so that you can study them later.

Take part in the discussion. Ask questions as they occur to you (or note them and ask them at the end of class).

Chat sessions in science subjects frequently involve discussion of mathematical calculations. One convention we use is underscore (_) for subscript and up-arrow (^) for superscript. The term **x_1 ^2** means "take the value x-sub-1 and square it". You may be more used to seeing this written as x_{1}^{2}, and we can actually do that in Dr. Bruce's chat, but it requires a bit of typing. If you prefer to use HTML tags, then here's a quick guide:

- Subscripts are written with the HTML <sub> tag. Be sure to use the closing tag </sub> or you may wind up with material too small to read! The sequence v<sub>0</sub> typed into chat will look like v
_{0}. - Superscripts are written with the HTML <sup> tag. Be sure to use the closing tag </sup> after your exponent or indicator. The sequence 10<sup>3</sup> typed into chat will look like 10
^{3}. - You can use unicode to indicate special characters. α will print as α, frequently used to designate angles. There is a good guide to unicode characters at TNT Luoma HTML Codes.
- We have implemented ASCIImath notation in the Scholars Online Chat. This allows you to type even complex mathematical formula relatively easily. To use the ASCIImath syntax options shown the ASCIImath.org site, type a RIGHT curly bracket symbol
**}**as the first symbol on a line. Your entry will be translated before uploading to the server. A line like}F_g = (GMm)/r^2

will appear as $${F}_{g}\text{}=\text{}\frac{\mathrm{GMm}}{{r}^{2}}$$

Your teacher will provide more instructions during the first few chats.

After chat, log into the chat window again, hit the button for past chat logs, and print the log out. As soon as possible after class, review the log and make notes on it about any points that bother you, and be sure to ask about these in our next session. Mark important points for review later. Consult your notes or the Scholars Online copy of the log to review before the next session and before semester examinations

All the examinations (quizzes, midterms, or semester exams) which I use to evaluate your understanding and progress in the course will be based on the mastery exercises and individually-assigned problems draw from the text. It is therefore very important that you complete your homework assignments, study questions, and any reports assigned to prepare for the exams for this course.

There will be an online quiz for each chapter, which will be available on the Moodle when we have finished discussing the material in the chapter. You must complete the mastery exercise with a passing score before you will be allowed to take the quiz. These quizzes include 10-30 multiple choice, short calculation, and other format questions and are timed. When you take the quiz, you will receive immediate feedback for your attempt. You will have a chance to take make up any missed quiz during the grace period before midterm exams.

Start your review two weeks prior to the scheduled examination.

- Go through the vocabulary used in the text. These may appear in boldface in the text materials, or be listed as concepts at the end of the chapter. Are there terms or concepts that you still don't understand? Note them down, and look them up. If you still have trouble remembering the meaning of the term, make a flash card for it and drill yourself, and be sure to ask for clarification during our review sessions (or sooner)!
- Re-read the summary sections at the end of each chapter covered by the exam. These often list the main points (and formulae, if any!) of the chapter. You should have any information in these points memorized, and you should be able to explain and use this information to analyze specific situations or solve mathematical problems.
- Review the chat logs, and go over your notes.
- Review your performance on the mastery exams and quizzes, and make a list of the concepts with which you are still unfamiliar or which still puzzle you.

There will be several major exams (midterms), after major sections of the text are completed. These may be mailed electronically to you, or you may take them on the Moodle. Either way, you will need your parent or other responsible adult to act as as proctor. If you take the exam (or part of the exam, such as the multiple choice section) in the Moodle, you will need to complete it before it closes. If I email the exam to you, or if you take the problem section of the exam on paper, you will need to type or scan in your answers to a computer file, and upload the file to the Moodle assignment for that exams before the assignment closes.

Most exams will include a multiple-choice or other format objective section, an essay section, and a problem section, and an "lab" section which involves analysis of observational data. All sections are closed book — you may not refer to a textbook or other resources.

HCOURSE is Physics

For Physics, Chemistry, and Astronomy, you may bring to these exams one 8.5 x 11 inch sheet of paper with whatever notes on it that you desire — so don't worry about memorizing formula. Learn concepts and applications!.Yes, of course you may study together — remember that explaining or teaching what you just learned to someone else is one of the important techniques of learning! You may also work together to solve individually-assigned problems or essay topics, and mastery exercise quetions. Be sure that you can complete all homework assignments on your own afterwards, since you cannot work as a study group on quizzes or examinations. Let me know if you need special chat times for your study group.

One of the basic methods of science is to secure documented observations of periodic or common events in order to make some general summary about the behavior of natural objects. We can do this in several ways.

**Directed observation**All observations of stars and planets, most observations of plants and animals in their native habitats, and many observations of geological specimens and meteorological events, are "field" observations. The situations must be allowed to occur without human direction, either because such direction is impossible (we can't control when a star will go nova), or because human intervention would interfer with the observation (we don't want to feed animals if we are researching their eating habits in the wild). The best we can do is make many observations of phenomena that are as similar as possible.

**Laboratory-based experiments**Laboratory-based observations are much more tightly controlled. Specific techniques and equipment are used for particular kinds of data collection. The experimenter can often vary only one factor at a time to see how it affects other dependencies. This allows many experimentalists to compare their results easily.

**Surveys**Frequently, research in one area reveals a tendency for a particular phenomena\on to behave a certain way. Rather than simply starting to observe the phenomena anew, one may choose to go back through past observations, looking for the same patterns or evidence of how nature behaved in similar circumstances. Surveys of historical data are common in weather studies, where such records exist for periods of 100 to 150 years, and in astronomical observations.

Surveys of experimental data have been somewhat uncommon, since most researchers prefer to redo an experiment with questionable results. This is changing, however. We are beginning to realize that data collected for one purpose as collateral data, for example, temperature readings as part of astronomical observations to determine air movement, may become important information for another study altogether, such as climate change over several centuries. There are literally thousands of astronomical photographs languishing in observatory archives which have not been evaluated in the light of modern discoveries, as well as millions of photographs of plants, animals, and single-celled organisms taken for one study that may reveal trends if examined for a different purpose.

Physics experiments, while they usually pose fewer dangers than chemistry, can still cause injury if students do not follow basic safety rules. Before you start experimenting, review the safety guide. Carefully read and follow safety guidelines for individual experiments, and study any safety information that comes with substances and equipment that you may purchase to complete your experiments.

Your lab report is the evidence of your observations of a particular phenomena. Your observations should be presented in such a way that the data is easy to understand and supports your conclusions, but also with enough detail on how you obtained them that any peer with similar equipment could repeat your experience and confirm your results (or challenge them, as the case may be).

**Organization**: A good science lab report has at least seven sections:

**The abstract**: a short paragraph explaining the goal of the lab, the overall purpose or hypothesis, the type of data gathered, and the conclusions.**Materials and equipment**: a description of the consumable materials and the observing equipment, instruments used to collect data. For standard equipment, references to the make and model are generally sufficient, along with verification that the equipment was tested for proper calibration.. If the equipment was modified, or specially configured, describe the new settings. If the equipment was specially built, either summarize the intent and purpose of the equipment and methods of calibration, or refer to other documents which provide this information.**Procedure**: a description of the process (in the case of a complex process, a list of steps) taken to secure the data. This should be detailed enough to allow peers in the field to repeat the measurements you made under simillar circumstances. Any choices you made that might affect results should be stated, along with the reasons you made them.**Raw Data**: the numbers you copied from instruments, descriptions of what you saw with your own eys, notes to yourself about odd things that happened, and rough sketches made during the observation. They might also include photographs, data collected by computer, and so forth. In many cases, the amount of data collected this way exceeds the space available in a formal report, so you do not need to include all of it. You should select representative samples of this data, and retain your notebooks with the actual raw data for reference if anyone questions your results.**Sample Calculations**: at least one each of any calculations you did to determine reliability (statistical analyses) or to figure out derived data (e.g., density from volume and mass measurements). This allows a reviewer (such as your teacher) to determine whether you used the proper technique of data reduction in this situation.**Processed Data**: all the processed data on which you base your results in the most useful forms. Frequently this involves creating a table, and may additionally involve preparing graphs to show trends.**Conclusions**: your assessment of whether your originaly hypothesis or assumptions are supported by actual phenomena. If your results did not bear out your assumptions, but you still feel the assumption is correct, you should explain the source of the problem (errors in measurement, calculations, equipment), and outline a plan for redoing the observations. When your experiment bears out your hypothesis, your conclusion should place these results in the context of the large field, and could include suggestions for further research.

Most Units will have links to further reading, interactive activities, simulations, or videos. These have been chosen to give you some exposure to resources for studying science — both learning methods and methods for advancing science itself. These are clearly marked **Optional**, so you may chose which areas most interest you to investigate.

© 2005 - 2018 This course is offered through Scholars Online, a non-profit organization supporting classical Christian education through online courses. Permission to copy course content (lessons and labs) for personal study is granted to students currently or formerly enrolled in the course through Scholars Online. Reproduction for any other purpose, without the express written consent of the author, is prohibited.