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 31College Physics I

Winter/Spring 2005

 Dr. Allan PringleCourse Instructor

Room 122 Physics, 341‑4031

pringle@umr.eduhttp://www.umr.edu/~pringle/phys31

Text

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.

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

*You may not be happy about the starting time! Neither am I. The best thing to do is deal with it and move on.

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.

Hour Examinations and Final Exam

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.

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.

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-of-semester 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!

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.

Three Exam Scores 600Eight Quizzes 120Boardwork 80

Total 800

Make-Up Policy

See the syllabus for procedures for incompletes and for taking an exam if you are out of town on an official university event.

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.

*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.

Wednesday, January 12Lecture 2: 3.4, 2.1Read: 3.4, 2.1Homework: 1.9, 1.26, 1.36, 3.1Special Math and Vector Homework #1

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.

This is what I plan to lecture on.

Reading and homework you should have completed prior to coming to class on January 12. This and all prior material is “quizzable.”

Not in your text, so I’ll have to hand this out in class on January 10.

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 10Lecture 1: Chapter 1, Appendix A, 3.1-3.3Read: Chapter 1, Appendix A, 3.1-3.3Homework: none

Wednesday, January 12Lecture 2: 3.4, 2.1Read: 3.4, 2.1Homework: 1.9, 1.29, 1.36, 3.1,Special Math and Vector Homework #1

Friday, January 14Lecture 3: 2.2-2.5Read: 2.2-2.5Homework: 3.7, 3.10,Special Math and Vector Homework #2

This is just a sample. “Official” assignmentswill be posted on the Physics 31 web page.

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

Unresolved Complaints

You can send e-mail to me at pringle@umr.edu. If you send e-mail from a Hotmail account or a friend’s computer and want a reply to your UMR account, be sure to include you UMR e-mail address.

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).

Jan. 101,3.1-3.3,A

Jan. 123.4,2.1

Jan. 142.2-2.5

Jan. 17no class

Jan. 19PLC

Jan. 21Boardwork

Quiz 1

Jan. 242.6-2.8

Jan. 263.5-3.7

Jan. 284.1-4.6Quiz 2?

Jan. 31PLC

Feb. 2Boardwork

Feb. 44.7

Quiz 3?

First Four Weeks Schedule

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.

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!

Chapter 1Introduction

What is Physics?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.”

Skip to here in lecture.

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…

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.

King Henry I (1068-1135) “decreed that 1/3 of his arm’s length would be the standard measurement for the foot.”

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.htmlhttp://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.

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.

http://www.skyscopes.com/scope/motions.html

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.

Showing all units in every step can be tedious.

If all your input parameters use SI units (mks), then your answer will be in SI units.

Do, however, show the units for your answers.

Example of unit conversion. How many seconds are there in a 365-day year?

365 days 24 hours 60 minutes

year day hour

60 seconds = 31,536,000 seconds

minut

1 yea

e

r

Units in Problems

365 days 24 hours 60 minutes

day hour

60 seconds = 31,536,000 seconds

mi

1 year year

nute

365 days 24 hours

1 year year day

60 minutes

hour

60 seconds = 31,536,000 seconds

minute

365 days 24 hours 60 minutes

1 year year day

60 seconds = 31,536,000 seconds

minute

hour

365 days 24 hours 60 minutes1 year

year day hour

60 seconds = 31,536,000 seconds

minute

Chapter 3Vectors 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

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 anything that can be represented by a number (with a + or - sign) and any associated units.

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.

A vector has both a magnitude

Vectors

A vector has both a magnitude and a direction.

Use boldface and larger font size, e.g. X is a vector…

How to Write a Vector

…or use the letter that symbolizes the vector with an arrow above it:

x

x ...

…or use an arrow with the letter:

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:

Magnitudes are always positive!

A vector can never equal a scalar. Never write

A = A .

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

Pi

Pf

D

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.

An object may undergo several successive displacements.

The net or total displacement is the vector from the starting position to the final ending position.

Pi

Pf

D

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.

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.

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.

Graphical Method for Adding Two Vectors

Makes me tired just thinking about doing all that.

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

B

A B

A+B

A

“Slide” vector B so that its tail touches A’s tip.

The “resultant” is the vector resulting from the operation (in this case, addition).

B

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

BA+B

A

“Slide” vector B so that its tail touches A’s tail.

A

B

Complete the parallel-ogram. The resultant is the diagonal.

B

Both the tip to tail and parallelogram method produce the same resultant.

A B

A+B A+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

B

1

A+B

A

B

3

A

B

2

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:

Commutative: C = A + B = B + A.

B

A

B

A

CB

A

C

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.

A + B B + A

Vector Multiplication by a Scalar

If a is a scalar then is a vector parallel to and a times the length of .

BC = 2 B

C = 0.5 B

C = -2 B

Subtraction of VectorsMultiplication of a Vector by a Scalar

C = aBB

B

can be longer than (if a>1) or shorter than (if a<1). If a is negative, then is in the opposite direction to .

C

B

B

B

C

Vector Subtraction

To subtract from , just add to :

BA

-BA

-B

A

C

A

-B

B

A

C = A -B = A + -B