Physics 10 Lecture 1

Professor Smoot's Class

Things that students should expect to get from taking Physics10: There is more on these topics below.

Physics As a World View

The text book is Physics: A World View. Indeed, physics is a world view. It is a way of looking at the world and its events. One takes a specific and systematic approach towards understanding and explaining events.

Why should we view physics (science) as an important world view worth learning? Some of you have learned that the general present view is that every culture's world view is equally valid in its own frame of reference. This is called `Cultural Relativism' and is generally held to be a useful view. In a more extreme form it is what is referred to as `Political Correctness.' Why does the University have a science elective requirement? What is there about science and physics, in particular, that makes them so important? After all there have been some that criticize science as being a Western white-male-dominated and biased system. There are two reasons:

First, science (physics) is a very powerful world view. As an example, how many of you have flown? (Most students raise their hands.) How many of you have flown on something besides an aircraft built based upon scientific principles using standard engineering and technology? (No students raised their hands.) This is just one example out of many you can see around you from the electronics, telecommunications and computer technology you use everyday to automobiles, elevators, and other complicated mechanical devices. It does not take very long to realize that nearly all the sophisticated devices you utilize everyday are based upon the principles of science and the technology and engineering that accompany those principles. Physics is the study of the fundamental principles of the physical sciences. As far as world views go, it is clear that science is in the first rank.

Second, science is an interesting world view in that it is based upon a self-correcting system. It is a part of the operation of science to do experiments to compare the world view, i.e. scientific models, with the actual world in the form of the results of controlled, well executed experiments. This is a form of natural selection of the world view or scientific knowledge. Often may models are proposed and the one that best fits the observations is the one that is kept. Science is a human invention that is very parallel to Natural Selection. The `knowledge' or `model' is the information encoded in genes. The comparison of this `world view' is handled by natural selection. Small or large variations in the genetic world view material is subject to the test of survival.

Supplements to the Text

There are two supplements to the text which you receive at no additional charge when you purchase a new text. These are not mandatory but are useful for you. The first is Environmental Issues which is a very nice write-up of some very important issues and it has a section on resources for your future reference. As you should learn in this course environmental issues are likely to be very important for most of your life. This will require learning about exponential growth and entropy.

One of the things that makes physics (science) so powerful as a world view is its ability to predict and describe things accurately. Ultimately, this requires expressing them in terms of numbers. The second supplement A Numerical World View provides assistance and a review of basic math, i.e. up to simple algebra, with material directly related to the text book and problems. This will allow working of problems with numerical answers. The course is not based on grinding through calculations; however, sometimes one cannot truly understand a concept without determining a numerical answer, including proper units. and

What Students Should Get From This Class

A few general comments. First the course will teach students how to think about scientific issues. Despite the fact that many call Physics 10 "Physics for Poets", I call it "Physics for Congressmen" because that seems to represent more accurately the enrolled population. The course is designed for intelligent people - the kind of student at UC Berkeley. Finally, the class should be fun and enlightening.

A basic understanding of physics.

Physics is the fundamental basis for all of the sciences, including chemistry and biology. It lays the ground work for these disciplines, and provides general principles that can be applied across the board. Physics is also something of great intellectual interest. College is one of the only times in a person's life, when they learn solely for the sake of learning, rather than for some immediate application, this course should satisfy your intellectual curiosity as well as provide a fundamental framework and foundation of knowledge. Physics represents one of the great intellectual achievements of mankind.

Science is a human endeavor.

Science is a human endeavor in many ways, meaning that as a discipline, it has imperfections. For example, there are successes and failures in science, and some people make fantastic discoveries and advances but may also participate in terrible acts. Science is not as clean-cut as it may seem; there is a great deal of personality to it. On the other hand, science is an organized system, and much like a corporation, it allows many different people to contribute and make advances, e.g. discoveries.

Skills and Confidence to use physics in your life.

From this course you should acquire the skills and the confidence to apply science (physics) to your life, perhaps not in a specific way but in a general way. One such area might be the environment; another is being able to understand and evaluate scientific articles that appear in newspapers and magazines. Much legislation involves science and one must be informed enough to be able to make educated judgements on these issues.

General Statements about Science

Fundamental Basis of Science

There is no fundamental basis for science, a fact that most scientists are loathe to admit. Science used to be called "Natural Philosophy," but over time a split between science and philosophy occurred, and eventually science became the part that claimed "things that are true" or "things that are known to be true." (This, of course, was to the dismay of philosophers.) Despite this description, there is no fundamental basis for science. For example, just because the sun rose today, and every day for 4 billion years, does not mean it will rise tomorrow. The way nature works may well change at any time. Despite this, scientists make the logical bet that the fundamental way that the physical world operates is independent of time.

"Order to Nature"

The are two important features necessary for science: order in nature and objective reality. The idea that nature follows a logical order does not seem so strange to us. However, we are living in a world long used to the idea. The ancient Greek Pythagoreus (famous for the Pythogorean theorem) started a school of followers based on the notion that nature can be described by numbers and followed a regular pattern, hence the term "order of nature". This was threatening to the leaders of the various religious sects devoted to the different Greek gods, since if Pythagoreus's idea became popular and believed, the public would no longer follow the gods and would cease making offerings and devotions. The end result was that Pythagoreus was exiled to Italy where he lived until 80 and continued teaching his following.

We also assume that the rules that describe the order of nature are basically simple - meaning that humans can eventually discover.

Objective Reality

Objective reality has to do with the idea that events may be different depending upon one's point of view. At some level our interpretation depends upon our view but the description of the actual things that happen during an event are held to be the same independent of the beliefs or interpretation of the observers. In science, if one person demonstrates a principle, a competent observer should be able to repeat the demonstration and get the same results. We have to be careful to distinguish between what happened and our interpretation of what happened. There is a certain skill and experience needed to determine what is the objective reality of an event and what is our interpretation of the event. The following demonstration will help to illustrate this point.

Demonstration

Demonstration: Objective Reality

This is an attempt to describe the objective reality of the demonstration.
schematic of floating bag experiment.

The professor lights a Bunsen burner and places it under a long pipe. A thin polyethelene (dry cleaners bag) with a wide mouth is placed over the top of the long pipe. The bag begins to swell up until it appears full and stands up straight. When it is released, it rises toward the ceiling of the room. It then tips, collapses together and slowly falls back to the table or floor.

What happened? That is what we try to describe in a way that that all competent observers would agree upon. That is the objective reality.

Why did it happen? is a question that requires interpretation. It calls for an explanation.

Nature of an Explanation

Physical Principles and Laws

In this case the two principles are Applying these two principles to the hot air bag is straightforward. When the air is heated, according to Gay-Lussac, it expands. Thus, it displaces a quantity of cooler air, outside the bag, that is heavier than the warm air inside. According to Archimede's principle, the immersed body (namely the bag of warm air) is buoyed up by a force that is greater than its weight. Therefore the bag rises to the ceiling. When the air cools or when the bag tips and the warm air leaks out, the weight of the bag is sufficient to cause it to descend.

Archimede's principle and the law of Gay-Lussac are examples of empirical laws. The have the form: "When A happens, B follows." An empirical laws describes, as accurately as possible, what takes place. It does not usually give much insight into why it should be true. This type of explanation is characteristic of relatively new fields of science.

More developed areas have models and theories that give more insight and connections to other bodies of knowledge. A good example of this is the kinetic theory of gases which we will study later in the course. It holds that gases are made of atoms and molecules and that these obey Newton's three laws of motion. From these assumptions we can derive Archimede's principle and Gay-Lussac's law and from that predict that the bag with the heated air inside will rise when the combined weight of the bag and the heated air is less than the weight of the displaced ambient air.

Scientific Theories & Models

The next lecture will talk about theories and the criteria for their acceptance, use and begin on the description of motions.
The explanation of an event or result is done by  theory. The theory is comprised of a model and relevant principles.
An example is the kinetic theory of gases which holds that gases (fluids more generally) are comprised of atoms and/or molecules which move and interact according to Newton's laws. From this model we will be able to derive the model of a fluid and an ideal gas and then consequently Archimede's Principle and Gay-Lussac's ideal gas law. The model is that the gas is a collection of atoms and the principles are the manner of their interactions.
Criteria for Acceptance of a Theory (explanation):

Demonstration

Liquid Nitrogen Shrinking an Inflated Balloon

Liquid nitrogen is poured on a balloon inflated with air. The balloon shrinks down much smaller, practically collapsed. When the balloon warms it expands back to its original size.

(photo) illustration of Guy Lussac's law.