Welcome…
…to College Physics I.
Important Note
The next few slides summarize important
information contained in the course syllabus.
Please refer to the syllabus for details.
If there is any discrepancy between these slides and the
syllabus, the syllabus is the “official word.”
PHYSICS 31
College Physics I
Winter/Spring 2005
Dr. Allan Pringle
Course Instructor
Room 122 Physics, 341-4031
pringle@umr.edu
http://www.umr.edu/~pringle/phys31
Course Description
Physics 31 is a 3-hour algebra-based physics course. You
will be introduced to the fundamental ideas of physics,
including mechanics, heat, and sound. The prerequisite for
this course is a grade of C or better in Math 6 or its
equivalent. Students lacking the prerequisite may enroll with
consent of the instructor.
Text
The text is Physics, sixth edition, by Douglas Giancoli,
Prentice-Hall, publisher. This book is written for students
taking an introductory course in physics, and uses
algebra and trigonometry but not calculus.
Course Schedule
Physics 31 meets from *8:00-8:50, Monday, Wednesday,
and Friday. A preliminary set of homework assignments
through the first exam will be handed out along with this
syllabus. There are three scheduled hour examinations
and a final:
Exam 1 – Friday, February 11.
Exam 2 – Friday, March 11.
Exam 3 – Friday, April 15.
Comprehensive Final Examination:
Thursday, May 12, 4:00 –6:00 p.m.
*You may not be happy about the starting time! Neither am I. The best
thing to do is deal with it and move on.
Hour Examinations and Final Exam
The 4 exams will be worth 200 points each.
The exams will cover concepts and definitions, assigned
problems with minor numerical changes, and problems similar
to those assigned but requiring a deeper understanding of
concepts or more complex calculations.
You will be provided with an equation sheet and you may also
use one 3"x5" card and any calculator containing any
information you want. Note that assigned text material not
covered in lecture is testable.
Course Grades
The lowest of the four exam scores will be dropped. (The
Final can be dropped only if you attend 2/3 of end-ofsemester classes!)
There will be ten 15-point quizzes during the semester. The
quizzes will cover recently-assigned reading material and
MCAT-like problems. Your two lowest quiz scores will be
dropped.
A number of class periods will be devoted in part to student
presentation of their homework at the blackboard. 80
points will be given for boardwork. Those who spend time
at the board will perform better on quizzes and exams.
Points!
Three Exam Scores
Eight Quizzes
Boardwork
600
120
80
Total
800
Letter grades for Physics 31 will be assigned as follows:
716 - up
A (89.50%)
636 - 715
B (79.50%)
556 - 636
C (69.50%)
476 - 556
D (59.50%)
Below 476 F
There is no limit to the number of A's, B's, etc.
Make-Up Policy
There will be no make-up exams in this course. The
dropping of the lowest score is intended to accommodate
students who miss one exam due to hospitalization, illness,
family emergencies, mental stress, athletic events, etc.*
Similarly, because your two lowest quiz scores will be
dropped, there will be no makeup quizzes.
See the syllabus for procedures for incompletes and for
taking an exam if you are out of town on an official
university event.
*Dropping the lowest exam score is not intended to accommodate students
who fail to prepare properly for an exam.
Dropping Physics 31
The last day to drop this class without a withdrawal showing
on your transcript is Monday, February 21, 2005.
The last day to drop this class is Friday, April 15, 2005.
Any student who has missed a total of 4 graded assignments
of any kind and has an average score of less than 69.50% on
graded assignments may be dropped at any time.
Physics 31 Web Page
Let’s visit the Physics 31 web page.
Physics 31 Reading and Homework Assignments
“Lecture” specifies the material I will present in class on the given day. “Read”
specifies the material you should read prior to coming to class that day.
“Homework” specifies the material you are expected to master prior to coming to
class that day.
This is what I plan to lecture on.
Wednesday, January 12
Lecture 2: 3.4, 2.1
Read: 3.4, 2.1
Homework: 1.9, 1.26, 1.36, 3.1
Special Math and Vector Homework #1
Not in your text, so I’ll have
to hand this out in class on
January 10.
Reading and homework you should have
completed prior to coming to class on
January 12. This and all prior material is
“quizzable.”
On the next slide is a sample of a week of assignments. I will hand out a paper
copy of the actual assignments leading up to the first exam. You can always get
the latest version of homework on the web here.
Physics 31 Reading and Homework Assignments, Part 1
“Lecture” specifies the material I will present in class on the given day. “Read”
specifies the material you should read prior to coming to class that day.
“Homework” specifies the material you are expected to master prior to coming
to class that day.
Monday, January 10
Lecture 1: Chapter 1, Appendix A, 3.1-3.3
Read: Chapter 1, Appendix A, 3.1-3.3
Homework: none
Wednesday, January 12
Lecture 2: 3.4, 2.1
This is just a sample. “Official” assignments
will be posted on the Physics 31 web page.
Read: 3.4, 2.1
Homework: 1.9, 1.29, 1.36, 3.1,
Special Math and Vector Homework #1
Friday, January 14
Lecture 3: 2.2-2.5
Read: 2.2-2.5
Homework: 3.7, 3.10,
Special Math and Vector Homework #2
Homework and the PLC
Homework help will be available at the Physics Learning
Center (PLC). You may be able to excel in the course without
ever setting foot in the PLC. You may need to spend many
hours in the PLC every week just to receive a passing grade.
The PLC is open from 2:00-4:30 p.m. and 6:00-8:30 p.m. The
PLC operates in rooms 129-130 of Physics, with Physics 23
(and 31) help available on Tuesdays and Thursdays. Individual
tutors are also available. Visit the web site
http://www.umr.edu/~tutors for up-to-date information.
Caution: the homework is “light” for the first 2½ weeks, while
we review math and do preliminaries. Don’t worry, it picks up
after that!
Regrade Requests
If you want a quiz or exam problem regraded, write the
reason for the request on a sheet of paper, staple it to the
exam or quiz, and return it to me within one week from the
time at which the exam started.
Specify which problem you want regraded, and provide a
written statement as to why the original work which
appeared on the exam deserves more points.
Don't wait until the day the final grades are due and ask for
Exam 1 to be regraded. However, scoring mistakes (points
added up wrong, score recorded incorrectly) can be
corrected at any time.
E-Mail
You can send e-mail to me at pringle@umr.edu. If you send email from a Hotmail account or a friend’s computer and want
a reply to your UMR account, be sure to include you UMR email address.
Unresolved Complaints
It is hoped that any complaints about the course can be
resolved in a collegial manner through discussions between
student and instructor. However, if there are any complaints
that cannot be resolved, you may take them up with the
Physics Department Interim Chairman, Dr. Don Madison
(madison@umr.edu) or the Dean of the College of Arts and
Sciences, Dr. Paula Lutz (plutz@umr.edu).
First Four Weeks Schedule
Jan. 10
1,3.1-3.3,A
Jan. 12
3.4,2.1
Jan. 14
2.2-2.5
Jan. 17
no class
Jan. 19
PLC
Jan. 21
Boardwork
Quiz 1
Jan. 24
2.6-2.8
Jan. 26
3.5-3.7
Jan. 31
PLC
Feb. 2
Boardwork
Jan. 28
4.1-4.6
Quiz 2?
Feb. 4
4.7
Quiz 3?
Exam 1: Friday, February 11.
Some final observations, before we start the course material…
 Nature follows the laws of physics, regardless of how you
feel it should act.
 There is one* right answer to any physics problem assigned
in this course. All other answers are wrong.
 Learn from your mistakes and your successes.
 There’s nothing wrong with starting off ignorant about
something important. Just don’t stay ignorant!
*Except for the estimation problems in chapter 1.
Chapter 1
Introduction
I will not lecture about most of the material in this chapter.
The major themes will be interwoven throughout the normal
course material. Read the chapter anyway!
Skip to here
in lecture.
What is Physics? Duh, it’s anything that physicists do!
Rather than getting sidetracked by an attempted definition of
physics (which you’ll notice your text also avoids), I’ll offer this
definition of science:
“Science is the process of seeking and applying knowledge
about our universe.”
To do science we must measure, and to measure we must
have precisely-defined units of measurement.
We will usually use SI units: meters, kilograms, seconds.
Here’s how I heard the story of our standard
for length: in the old days, the king set the
standard for measurement. A foot was the
length of his foot.
Don’t laugh! With the ability to set standards comes power
and wealth.
Unfortunately, I have to report that our present-day foot was
not the length of somebody’s foot…
King Henry I (1068-1135) “decreed that
1/3 of his arm’s length would be the
standard measurement for the foot.”
With the French revolution came the idea that the standard of
length belonged to the people. A meter was defined as one
ten millionth of the length of the arc from the north pole to the
equator, through Paris, France.
With the definition of the meter in hand, surveying teams set
out to determine the meter.
This being during the French Revolution, it
proved hazardous work…
…and members of the survey team died
bringing you the meter…
…which they didn’t get right anyway!
http://www.metaphor.dk/guillotine/Pages/Guillot.html
Subsequent definitions of the meter
improved the accuracy with which it
could be measured, while minimizing
changes to the actual length.
A meter is now defined to be the length
of the path traveled by light in a vacuum
during a time interval of 1/299,792,458
second.
Interesting reading:
http://www.mel.nist.gov/div821/museum/timeline.htm
http://physics.nist.gov/cuu/Units/meter.html
http://www.sfu.ca/phys/100/lectures/lecture2/lecture2.html
http://www.sizes.com/units/meter.htm
A second was once defined as
1/86,400 of a mean solar day, except
a “mean solar day” varies constantly.
http://www.skyscopes.com/scope/motions.html
In 1956 the second was redefined as 1/31,556,925.9749 of
the length of the year beginning in January 1900.
Right. So you have to be an astrophysicist to measure time.
A second is now defined in terms of the frequency of radiation
emitted by a particular state of a cesium atom. You can see
the definition here, if you wish.
This is all you need to have a clock accurate to better than 1
second over 20,000,000 years.
Get your up-to-the second time here.
A kilogram is defined as the mass
of a platinum-iridium cylinder
stored in Paris.
Maybe some day we will devise a
more “scientific” definition of the
kilogram!
NASA can tell you why it is important to keep your units straight! I suggest you
not repeat their mistake.
Units in Problems
Showing all units in every step can be tedious.
Do, however, show the units for your answers.
If all your input parameters use SI units (mks), then your
answer will be in SI units.
Example of unit conversion. How many seconds are there in a
365-day year?
365 days 24 hours 60 minutes
1 year
year 


year
day
hour
60 seconds

= 31,536,000 seconds 
minut
mi
minute
nute
e
Chapter 3
Vectors and Scalars
Why did I skip chapter 2?
 to introduce you to vectors first
 to keep in synch with Phys. 23
“If you are in control, you aren’t going fast enough.”—Mario Andretti
Scalars
A scalar is anything that can be represented by a number
(with a + or - sign) and any associated units.
The symbol for the scalar includes the units: just write x
instead of x (m) if the units of x are meters.
A scalar is always written with a non-bold symbol and can be
positive or negative. The magnitude of a scalar x is the
absolute value |x| and is always positive.
Vectors
A vector has both a magnitude and a direction.
How to Write a Vector
Use boldface and larger font size, e.g. X is a vector…
…or use the letter that symbolizes the vector with an arrow
above it: x ...
…or use an arrow with the letter:
x
You don’t need to make the symbol boldface or put an arrow above it (not
wrong, but why do the extra work?). The length of the arrow represents
the vector’s magnitude and the letter symbol is its label.
The letter symbol alone is the vector’s magnitude:
A= A .
Magnitudes are always positive!
A vector can never equal a scalar. Never write A = A .
A vector can never equal a scalar. Never write A = A .
A vector can never equal a scalar. Never write A = A .
Addition of Vectors
In Chapter 2 we will define displacement as the change in
position of an object; i.e., the vector from the object’s starting
position to its ending position.
Pi
D
Pf
An object may undergo several successive displacements.
D
Pi
Pf
The net or total displacement is the vector from the starting
position to the final ending position.
To find the total displacement, we add the vectors from start
to finish. In a minute we’ll see how to add vectors.
If a vector has magnitude and direction, what about its
position?
We haven’t specified position in the definition of a vector, so
you can put it anywhere you want!*
*Of course, you must put it somewhere that makes sense, and make sure
the magnitude and direction are correct! Later, when we work with force
vectors, we will find we can only “slide” them along their line of action.
Graphical Method for Adding Two Vectors
Your text discusses the graphical method of adding vectors:
draw the vectors to be added using a ruler and protractor,
draw the resultant, and then measure the length of the
resultant with the ruler and its angle with respect to some axis
with the protractor.
Makes me tired just thinking about doing all that.
The diagrams for your problem solutions will
always display vectors graphically, but you will
always use mathematical methods (described
soon) to add vectors.
The next two slides show the two techniques you can use for
drawing your diagrams for vector addition.
Tip to Tail Method for Adding Two Vectors
Place the tail of the second vector at the tip of the first vector.
The resultant is the vector from the beginning tail to the
ending tip.
A
A
B
A
B
B
A+B
“Slide” vector B so that
its tail touches A’s tip.
The “resultant” is the vector resulting from the operation (in
this case, addition).
Parallelogram Method for Adding Two Vectors
The tail of the second vector is placed at the tail of the first
vector. The two vectors define a parallelogram. The resultant
is the vector along the diagonal of the parallelogram.
A
A
B
A
B
B
“Slide” vector B so
that its tail touches
A’s tail.
A+B
Complete the parallelogram. The resultant
is the diagonal.
Both the tip to tail and parallelogram method produce the
same resultant.
A
A
B
A+B
B
A+B
The magnitude of the sum is always less than or equal to the
sum of the magnitudes of the vectors being added; this may
provide clues to incorrectly worked problems.
What do you think of this:
A
A
A
B
A+B
B
1
B
2
3
BAD! WRONG! DO NOT TRY THIS AT HOME! (or in
class, either)
You never saw that done here!
Remember, vectors have both magnitude and direction. You
can specify a vector by:
 magnitude and direction (5 meters, northeast)
 magnitude and angle it makes with some axis (5 meters,
45 counterclockwise from +x axis)
 components with respect to axes (next lecture).
If a problem requires a vector as an answer, your answer
must provide information about both a magnitude and a
direction.
Vector addition is commutative:
A
B
B
C
C
B
A
A
A+B
Commutative: C = A + B = B + A.
Remember, if I write a vector symbol
as text and don’t use arrows over the
text, I’ll make the text large and bold.
B+A
Subtraction of Vectors
Multiplication of a Vector by a Scalar
Vector Multiplication by a Scalar
If a is a scalar then C = aB is a vector parallel to B and a
times the length of B.
B
C = 0.5 B
C=2B
C can be longer than B (if a>1) or shorter than B (if a<1). If
a is negative, then C is in the opposite direction to B .
C = -2 B
Vector Subtraction
To subtract B from A , just add -B to A :
B
A
A
-B
A
-B
C
 
C = A - B = A + -B