The Nature of Science
     The practice of science has a long and illustrious history. Science, in the western world, is generally thought to have begun in ancient Greece with the so-called pre-Socratic philosophers. Thales (624 - 546 BCE) is often cited as an important example as he proposed, among other things, that water was the single material on which all other materials are based. The Greeks were the first to ask, and attempt to answer, important questions about the nature of the universe without dependence upon mythological explanations.

     The famous Greek philospher Aristotle (384-322 BCE) is credited as a pioneer in such diverse areas of academic interest as biology, geology, ligusitics, ethics, and many others, but most importantly for us, physics. Aristotle was a student of Plato and a teacher of Alexander the Great. His influence stretched out over two thousand years. Of particular interest to us is his geocentrism, the notion that the Earth is positioned at the center of the universe. As we will see, the ideas of Aristotle were eventually replaced by those of Isaac Newton (1642 - 1727) as the best explanation of the workings of the natural world.

     Newtonian mechanics differed drastically from Aristotle's in many ways, not the least of which is the notion of heliocentrism, or a sun-centered system. Heliocentrism was promoted by several scientists prior to Newton's day (Copernicus, Kepler, and Galileo, for example), but it wasn't until the publication of Newton's famous text, Philosophiae Naturalis Principia Mathematica that humans began to see the universe as a giant mechanism. Newton's ideas are, however, now seen as an accurate description of only the medium-sized, slow-moving objects in our world. In order to gain an understanding of the sub-atomic world, or of the universe at large, scientists now turn to Quantum Theory and Einsteinian Relativity.

     Please don't view the process of new scientific theories replacing old ones as a weakness of the scientific enterprise. In fact, it is a strength of science that changes are made as new and confusing data become available.

     The changes in our scientific view of how the universe behaves has been the topic of a great deal of work in an academic area called "Philosophy of Science." For example, in 1962, with the publication of The Structure of Scientific Revolutions, the American author Thomas Kuhn coined the term "paradigm shift" to describe the times in history when the "normal" science of the day is replaced by a new and more explanatory science. Kuhn's broad background as a physicist, historian, and philosopher allowed him to identify the "non-linearity" of the scientific enterprise by showing how new paradigms are not built on old ones, but are instead prompted by anomalies in research that can eventually produce new theories that are drastically different from the old ones. The old and the new are not reconcilable. Additionally, Kuhn claimed that scientific truth is attained through a community of expert scientists and has a social component.

     The community aspect of the scientific endeavor is therefore an important part of the "practice of science." Educational researchers have recently promoted the idea that science students need to practice science in the classroom in the same way that scientists practice in the real world. That is why many of the activities you will be asked to perform in this course are "Inquiry-Based." That is, they are self-guided as much as possible, in the same way that natural curiosity guides the work of actual scientists in the field. Scientists are part of a community in which creators of claims elicit responses by critiquers of claims. The critiques may prompt new claims followed by further critique. This back and forth activity is an essential part of the way progress is made. The ultimate arbiter of scientific truth is the natural world, but the notion that science is socially-based helps to guide the understanding of science and the activities that should take place in the science classroom.

     The College Board has emphasized the importance of these ideas by publishing the following on pages 27-28 of the Teacher's Manual for AP* Physics 1 and AP* Physics 2:

"Throughout the study of the history and philosophy of science, there are 10 key points that have emerged about the development of scientific knowledge over time. In total, these points lead to one key conclusion: science is not a body of theories and laws but rather an approach to understanding observations that allows us to make sense of the world around us. If we think about these key points, they can help us understand the reasons for using inquiry in the physics laboratory.

These key points about the nature of science (as modified from McComas, 2004) are:

1. Scientific knowledge is tentative but durable.

2. Laws and theories serve different roles in science and are not hierarchal relative to one another.

3. There is no universal step-by-step scientific method.

4. Science is a highly creative endeavor, grounded by theory.

5. Scientific knowledge relies heavily, but not entirely, on observation, experimental evidence, rational arguments, creativity, and skepticism.

6. Scientific progress is characterized by competition between rival theories.

7. Scientists can interpret the same experimental data differently.

8. Development of scientific theories at times is based on inconsistent foundations.

9.There are historical, cultural, and social influences on science.

10. Science and technology impact each other, but they are not the same."

     Although each entry in this list is important, points 4, 5, and 6 take on added value in the context of AP Physics 1. That's because the AP exam is about more than calculations. It's also about using cognitive skills to effectively construct and critique scientific claims.

     The importance of lab activities in this course is supported by the aforementioned comments. For students using the resources at Physics Prep, the lab activites are most likely done by a single student carrying out an investigation. The lab notebook is thus an important way to eventually share the findings of investigations with others and receive feedback. Please follow the guidelines shown below so that your work can be shared in an organized and clear manner.

Objects and Systems 

     Throughout this course you will hear the terms "object" and "system of objects." The physics definition of an object is something that has no internal structure. This means that it can't be broken down into contituent parts. In other words, an object is not a composite of other objects. There aren't many things that meet this definition. Currently physicists recognize only 17 elementary particles that have no internal structure. Among these are particles you've encountered in your chemistry course: electrons, photons, gluons, quarks, bosons, and neutrinos. On the other hand, "particles" such as protons, neutrons, atoms, molecules, and indeed anything composed of them, are actually systems of elementary particles. So, since a block of wood is made of a huge number of atoms, each its own system of elementary particles (objects), it is a system of systems of objects.

     However, in physics practice, macroscopic objects like a block of wood can be modeled as "objects" when their internal structure plays no role in the solution to the problem being solved. For example, when a block of wood slides across a "frictionless" table, and the problem asks to find its macroscopic speed, the internal structure of the wood is unimportant to the problem. In that case, calling the block an "object" is common practice. In this course, you will learn a concept known as "center of mass." This idea allows us to assume that all of mass of the block, the system, is located at the center of mass position as if it was an object with no internal structure. However, when friction is considered, some of the energy of motion of the block is transferred into the constituent particles that make up the block in the form of heat. Some of the energy also increases the motion of particles that make up the surface of the table. So, while we can continue to call the block an object, the fact that it is a system of objects often needs to be considered. 

     Play the video below and ask yourself if the behavior of the objects that make up the system is the same as the behavior of the system as a whole. It's easy to see that the objects in the system are moving in straight lines relative to the wood plate, but the system is moving in a circle trajectory with a measureable rotational speed. So, depending on what you were interested measuring, the system could be called an object with it's own measureable properties or a system of individual objects, each with their own properties

     These terms will be used throughout the course. So, knowing them at the start is important. In summary, objects have no internal structure, while systems of objects do have internal structure. When the behavior of the constituent parts of a system play no (or very little) role in the explanation of a physical phenomenon, it's beneficial to model a system of objects as a macroscopic "object."

Measurement and Significant Figures

     When a scientist makes a measurement she uses a measurement device that will allow for a set level of accuracy that depends upon the physical characteristics of the device.  For example, look at the ruler being used to make the length measurement below.  One can say for sure that the measurement is greater than 11.6 cm, but the second decimal place in the measurement would only be a guess.

     The number of significant figures in a measurement represents all the digits that are known for sure PLUS one digit that is a guess.  The measurement made above might then be 11.65 cm.  But it would still be a valid measurement if someone used this ruler and claimed that the measurement was 11.64 cm.  Each of the measurements contains four significant figures.

     The College Board expects students who take the AP* Physics exams to understand the role of significant figures in measurement and to be able to determine the number of significant figures in the answers to problems involving the multiplication, division, addition and subtraction of measurements.  Since students taking this course are expected to have already taken a chemistry course, wherein the concept of significant figures should have already been covered, the rules below should act as a reminder of how significant figures are used...not as a tutorial.  If you want to see more information on significant figures click here to find an entry on Wikipedia.

     A quick note regarding significant figures and unit expression...you will notice that attention to significant figures is not always a high priority when computations are done during the presentations for this course.  Reasonableness in rounding is the rule when the concept being described is more important than attention to significant figures.  In other words, if the presentation is about magnetism, all the work shown will exhibit reasonable rounding in computations but not always strict adherence to the rules of significant figures.  Additionally, much of the work done will only show the units in the final answer of the calculation rather than in each step along the way.  Again, priority is given to efficiency in learning the concept at hand rather than making the problem look busy with unit notations.  

The rules that you should know in this regard are are follows:
1. All non-zero numbers are significant.
2. Zeros within significant digits are always significant. (Ex: 809 has three significant figures)
3. Zeros that are "place-holders" are not significant. (Ex: 0.0082 has two significant figures)
4. Trailing zeros that aren't needed to hold the decimal point are significant. (Ex: 20.00 has four significant figures)
5. When measurements are added or subtracted, the answer can contain no more decimal places than the least accurate measurement. (Ex: 21.47 + 1.1 = 22.6)
6. When measurements are multiplied or divided, the answer can contain no more significant figures than the least accurate measurement. (Ex: 5.156 x 2.3 = 12 because there are only two significant digits in one of the measurements being multiplied)
7. When answers are rounded off it is generally acceptable to round up if the last digit is 5 or greater and round down if the last digit is 4 or less. Different sources may site different rules in this regard.

(You might want to print this information and place it in a binder for future reference)

Quick Concept Check: Look at the image of the water bottle shown below. If you were asked to add the volume of water in the bottle to the same volume of water found in another identical bottle, what should you claim as the answer?

An acceptable measurement of the volume of water in the bottle is 20 oz., but 21 oz. or 19 oz. might also be reasonably read as the volume. In each case, the number in the "ones" place is a guess and there is only one significant figure in the measurement. It is in the "tens" place. Now, if you add 20 oz. and 20 oz. you get 40 oz., again with the single significant figure in the "tens" place.  What if another student made the reading as 19 oz.? Would the final answer change? No, because adding 19 oz. and 19 oz. would yield a prelimary value of 38 oz that when rounded off to the "tens" place gives the acceptable answer as 40 oz. once again. 

How to Keep a Lab Notebook:

Having a record of your labwork (in electronic or hand-written form) is a very important product of your work in this course.  For each lab activity you should use this structure in the lab notebook:

1. The title of the lab activity
2. The date the lab activity was performed
3. The goal(s) of the lab activity
4. A description of the lab activity (procedures, sketches, pictures, etc.)
5. Data collected in the lab activity
6. Analysis of data (graphs and sample calculations)
7. Analysis of error (when appropriate)
8. Conclusion(s) (What did you learn that you didn't know before performing the lab? Did you achieve your goal(s)...why or why not?)

Because some of the parts listed above may not be applicable for each lab, details in the lab assignment will list the parts of the report that must be included and those that are not required for that particular lab.

The lab report should be done neatly and completely in the lab notebook so that any university officials that ask to see your reports would be satisfied regarding the lab component of your work in physics.

Finally, lab safety should be of utmost importance whenever a scientist performs a lab activity. Please do not use any of the equipment called for in this course in any way that is not safe. Follow all instructions regarding the use of any lab equipment that can cause injuries to you are anyone else in the vacinity of your lab work.

• Before every lab, make sure you know and record the potential hazards involved in the investigation, as well as the precautions you will take to stay safe.
• Before using equipment, make sure you know the proper method of use to acquire good data and avoid damage to equipment.
• Know where safety equipment is located in the lab space, such as safety goggles, and a first aid kit.
• Follow any special safety guidelines as set forth prior to each experiment. (Students should record these as part of their design plan for a lab.)
• When in doubt about the safety or advisability of a procedure, check with the teacher before proceeding.

Take the Quiz
Click here to take the quiz after you have carefully read all of the material above.