Physics 141

Physics Department

Cal Poly

San Luis Obispo

The Laws of Motion, Forces, Energy, Momentum
and the Conservation Laws

It is the most persistent and greatest adventure in human history, this search to understand the universe, how it works and where it came from. It is difficult to imagine that a handful of residents of a small planet circling an insignificant star in a small galaxy have as their aim a complete understanding of the entire universe, a small speck of creation truly believing it is capable of comprehending the whole.

- Murray Gell-Mann, Caltech physicist

Last updated:  December 10, 2014

General Physics: Mechanics

An introductory calculus-based course in classical mechanics - the first course in the physics sequence. Topics include the description of motion, Newton's laws, the concepts of work and energy, impulse and momentum, and torque and angular momentum and the three conservation laws (energy, momentum, and angular momentum) that characterize the motions of objects and the principles that govern their motion.

The course will meet four days per week - MTuWTh 5:10-6:00  - Science North  Bldg 53-213).

Instructor: Dr. Ron Brown - Physics Department

Textbook:   PHYSICS FOR SCIENTISTS AND ENGINEERS, 3rd Ed.,  by Randall Knight, Pearson (2012)

                     PHYSICS 141 Supplemental Notes and Problems, by Ron Brown, El Corral (2008)

Course Syllabus


Physics 141 Topics and Notes


Great Ideas that Have Changed Our Worldview - An essay

Physics Central - A great link!


   This course will deal with the basic ideas of forces and motion - its description and the principles that govern it. The topics of the course include the description of motion, Newton's laws, the concepts of work and energy, impulse and momentum, torque and angular momentum - and the three conservation laws that govern that motion - and how to use those ideas and principles to solve problems. But it will also deal with much more. What you should gain from this course is an understanding of the way that science works - the critical method of how our ideas about nature are formulated. It is this that you will ultimately carry with you long after the specifics of the course have waned from your memory.

While studying how to solve problems involving motions of objects, we want to also consider grand questions like: Why do things fall with the same constant acceleration (and do they always)? What IS gravity? What is the law of gravity that ultimately governs the motions of falling objects, the planets, and the stars and galaxies? How can we know the mass of the earth (and why would we want to)? Why are the planetary orbits elliptical? (And, by the way, how do we even know that our planet is orbiting a small star 150 million kilometers away, anyway?) What can we know - and on what can we merely speculate?

Science is ultimately about ways of knowing - how we know what we know.


Note: This is the 3rd edition of this text.  You will use the same book in PHYS 132 and 133.

     •  Supplemental Notes: Physics 141 SUPPLEMENTAL NOTES AND PROBLEMS   by Ronald Brown (El Corral)

The supplemental notes are intended to be used along with the text to relate the important ideas of the course. The supplement should give you a little different perspective and approach to the material of the course. The order will be different than the text in places. It is recommended that you read both presentations carefully.  References will be made to both the text and the supplemental notes throughout the course.  The supplement is available in El Corral with the physics textbooks.

The Supplement is about 100 pages or so covering kinematics, Newton's laws, work and energy, momentum, and rotational motion. The notes are intended to support the text - and focus on the fundamental concepts, ideas, and principles related to each of the topics and on tying the principles together and leaving you with a strong conceptual understanding.  Each section concludes with a set of conceptual questions and problems to help your study.

Learning Center Hours: Mon. 9 am - noon; Tues., Wed. 9 am - 2 pm; Thurs. noon - pm; Fri. 9 am - noon.

NOTE: Hours may change when Center opens the second week of classes.

Tips for Studying Physics
The Whys and Hows of Physics Problems
Solving Problems in Physics


[Look here for comments related to this section of Physics 141.]

This class is scheduled to meet twice a week - Monday and Wednesday from 6-8pm - for lecture and discussion.  The format will include some lecture and some discussion each day - with occasional problem solving "workshops".  Problems will be worked on both individually and in groups. It will be expected that you will attend class regularly having read the related material in the text and the supplemental notes and that you will have worked on problems (those in the text, the workbook, the supplemental notes) - so that the work done in class is not your first exposure to that material.   Any homework that is actually collected will be problems from the supplemental notes or from individual problem set worksheets.

You are welcome to come to my office to discuss the course or physics or anything else, for that matter, at any of my office hours or whenever it is convenient for you. If you can't meet my office hours - and can't find me just by dropping by, email me to set up a time to meet.

Expect a diagnostic "pre-test" to be sent out prior to the first class.  It is intended to be a way for you to check yourself to see if you are comfortable with the mathematical ideas that are assumed to be a part of your background.  You may submit the pre-test the first day of class if you want me as your instructor to evaluate how you did and return it to you the following class meeting.  This exercise will not count toward your grade in any way - it is just diagnostic on ideas that will be made use of during the quarter.

<>The First Week

<>You should read the Introduction of my Supplemental Notes and Problems booklet to get an idea of what is expected in this course and what studying physics is about.  Then we will begin what is the central theme of this course:  Forces  - what they are and how they act.  By Wednesday, you should certainly have read Part I of the Supplemental Notes on Forces and should be starting to address some of the problems.
<>By the end of the week, we will begin the formal discussion of motion - including developing the equations that describe the motions of objects in a straight line.  This subject, kinematics,  will be an important part of the next few weeks, and you need to have a good understanding of the equations, where they come from and how to use them.  You should be reading the textbook to help you make the connections between the motions of objects and how to describe the motions of objects.

Week No. 2:

We will continue with the developement of the kinematics equations in one-dimension and make the connection between the equations, the description of motion, and the graphical representations of the motion.  The discussion will include free-fall problems (which are the basis for all projectile motion problems, as we will see).  By Wednesday, we will return to the mathematical description of vectors, so that the mathematical development of the one-dimensional motion can be extended to two and three dimensions.

There will be a short quiz on the material of the first week.

Week No. 3:

In the first couple of chapters, we have been building the tools needed to deal with Newton's laws.  This week, we will start making the connection between the forces that act on an object and the resulting changes in motion.  On Wednesday, we will talk about any of the projectile motion problems that offered difficulty - and will extend the discussion of two dimensional motion to circular motion problems (something we will come back to in later chapters).  That discussion will lead to Newton's development of his three laws of motion (and even his law of gravity).  Given the background of how to describe motion in two dimensions (which, in general, requires making use of vector notation), and the understanding that forces are always interactions between two objects, we will be able to show how knowing the forces that act on an object will lead to a complete description of its motion.

There will be a short quiz on kinematics during the first part of class.  It will just be one or two problems that are based on the ideas covered so far on the description of motion in one and two dimensions.  The problems will be similar to those you have already seen in the HW and others in the Supplemental Notes.

Week No. 4:

Newton's Laws.  The connection between forces and motion.  Be sure and read Ch. 4 and the section on Forces in the Supplemental Notes and Problems booklet.  We will talk about Newton's three laws - what they mean and how they apply to problems - and Newton's law of universal gravitation.  These pieces will lead to tying together all the pieces we have been discussing the first few weeks.  We will first concentrate on force problems that result in one-dimensional motion.  Then the discussion will turn to problems in two dimensions which will include projectile motion problems and problems that involve circular motion.  These dynamics problems are about how the relationship between forces and accelerations can lead to a complete description of the motion of objects.

Problems:  Ch 4 - 1, 9, 26, 47;   Supplemental Notes and Problems:  Forces - Problems 7, 8, 12, 13, 14, 16

Week No. 5:

We will continue with the applications of Newton's laws on Monday - and will answer questions on the Ch 5 HW problems if you have them.  Look in particular at particular at problems that involve two object which are somehow connected - ie, either by a string or rope or by physcal contact through normal force or friction.  The idea for problem such  problems for the acceleration due to the forces that act is to first separate the problem into two problems - drawing the force diagram on each object and writing the corresponding force equations and then solving those equations simultaneously.

Chapters 6 and 7 will then expand the discussion to include two and three dimensional motion - ie, force problems when the motion is not reduced to only one dimension.  We have already done some of what appears in Ch 6 - projectile motion problems.  Ch 7 deals with the description of circular motion problems.  We will be in that material by Wed. 

Ch 5 Problems:  6, 10, 17, 19, 27, 34, 35, 40, 51, 55, 57, 70 and Supplement:  Newton's Laws - 4, 6, 13, 17, 18, 19

                                                                                                    EXAM I

The exam will cover material up to through Ch. 5 including Newton's laws and the application of Newton's laws to problems involving motion in one dimension.  The test will include both conceptual questions and problems to solve.  This will actually be one of a two-part exam.  Part B will be the following week in lab and will include the extension to problems involving two and three dimensional motion including circular motion problems, gravitation, and orbit problems.

Week No. 6:

On Monday, we will deal with the circular motion - and orbit - problems of the assignment that's due, the car on a banked turn, and then problems involving objects which are connected together (for example, blocks tied together by a rope).  All of these problems are just applications of Newton's second law - and are approached in essentially the same way.  The only issue to always keep in mind in circular motion problems is that the net force has a component toward the center of the circular path - and the acceleration in that direction is always v2/r.

Chapters 7 deals with circular motion.  You should also look in the Supplemental Notes in the section on Kinematics.  (That is just a brief description, but the centripetal acceleration is derived for uniform circular motion.)  Chapter 8 deals with Newton's Third Law - and how objects interact with each other (something we've been talking about all along).  Look in particular at how to deal with problems that involve two objects whose motions are related to each other - for example blocks sliding on other blocks or pushing each other or tied together by ropes, etc.

Ch 7 Problems:  15, 17, 18, 30, 44 and Supplement:  Kinematics - 13-16 (circular motion problems); Newton's Laws: 21, 22, 23
Ch 8 Problems:  22, 30, 46, 44 and Supplement: Newton's Laws - 13, 14, 17, 19, 20 (connected objects)

Week No. 7:

Conservation of Momentum. By Wed., you should have read Ch. 9 on Impulse and Momentum and be working on problems involving collisions - like what we did in lab last week.  We will introduce kinetic energy into the discussion as well, since some kinds of collisions, while conserving momentum, also conserve kinetic energy and others do not.  The idea of the conservation of momentum follows directly from Newton's Third Law.

Problems:  Ch 9 - 33, 38, 53, 57;   Supplemental Notes:  Momentum and Systems of Particles - Problems 7, 8, 12, 13, 14, 16

Week No. 8:

You should be able to do momentum conservation problems in both one and two dimensions - including elastic and inelastic collisions.  We will begin the discussion of energy - which will involve the concepts of work and both potential and kinetic energy.  The important Work-Kinetic Energy theorem leads to the principle of conservation of energy - one of most important ideas we will encounter.  It can become a powerful (and simple) tool to solve many problems.  The energy concepts of kinetic and potential energy, work, and the work-energy theorem appear in Chapters 10 and 11 - and the Supplemental Notes section Work and Energy.  I think it is helpful to look at all of that material together.

PHYSICS for Scientists and Engineers  by Randall Knight

        Chapter 1 - Concepts of Motion

Ch 1 Problems: 

        Chapter 2 - Kinematics in One Dimension  

Ch 2 Problems: 

        Chapter 3 - Vectors and Coordinate Systems

                            Ch 3 Problems: 

        Chapter 4 - Kinematics in Two Dimensions
                            Ch 4 Problems: 

        Chapters 5 - Force and Motion
                            Ch 5 Problems: 
                                           Supplement:  Newton's Laws

Chapters 6 - Dynamics I: Motion Along a Line

                            Ch 6 Problems: 

Chapters 7 - Newton's Third Law

                            Ch 7 Problems:  

Chapters 8 - Dynamics II:  Motion in a Plane

                            Ch 8 Problems:  

        Chapters 9 - Impulse and Momentum

Ch 9 Problems: 
and Supplement:  Momentum


Chapters 10 - Energy 

                            Ch 10 Problems:  
                                           Supplement:  Work and Energy

        Chapters 11 - Work 

Ch 11 Problems: 
and Supplement:  Work and Energy

        Chapters 12 - Rotation of a Rigid Body

Ch 12 Problems: 
and Supplement:  Rotational Motion



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