Welcome to
Principles of Physics I
(PHYS 2010)
Lecture 002 - 11:00-12:15 TuTh
003 - 12:30-13:45 TuTh
Professor Blaine Norum
Course website: http://people.virginia.edu/~kdp2c/PHYS2010_Fall2010/index.html
(linked from UVa Collab site)
Enrollment
If you are on a waitlist, you shouldn’t be. Come see
me.
- After class
- Tues & Thurs 15:00-18:00 (office hours, rm 136)
2
Course rules
Turn off cell phones.
Open laptops in last row only.
Do not interfere with the learning environment.
Make space for your fellow students.
If you are sick... don’t come to class.
Lectures
Format
• Electronic
• Slides
slides
will be available after lectures (rarely before)
demos to build intuition, relate to the real
world, and encourage engagement
• Frequent
I will occasionally miss a class. In this case, your
instructor will be another professor with experience in
this class.
i>Clickers
• Graded
“reading quiz” (2-3 problems) at start of lecture
more “participation” questions throughout class
(credit for any answer)
• Many
• These
will challenge your conceptual understanding,
encourage your engagement and provide me with
feedback
• Yes,
it counts for your grade (2%)
• Register
your i>Clicker: go to UVaCollab site.
Mastering Physics
A web-based homework system
• Instantaneous
• Multiple
• Hints,
attempts at problem solving (guessing discouraged)
tutorials, and other support
• Excellent
• Well
feedback
feedback to instructors
designed interface
• some
applets/simulations may be helpful
• MCAT
study guides (mostly practice MCAT quizzes)
Register using your access code at MasteringPhysics.com
•sign up for Walker 4th edition
•Use this class code MPNORUM36834 (2)
MPNORUM93099 (3)
•use your email/computing ID
•Problems: use the online help (“Ask a question”).
There is an introductory assignment (not graded) out now.
5
Exams and Grading
Midterm Exams:
Three midterm tests will be given at the dates and times shown in the syllabus. The tests will be
administered during regular class time. The tests will consist of multiple choice questions.
TEST DATES IN SYLLABUS ARE NOT WRITTEN IN STONE! THEY MAY SHIFT SLIGHTLY!
Final Exam:
Section 2: Monday, December 12 @ 9:00-12:00, Room 203
Section 3: Thursday, December 15 @ 14:00-17:00, Room 203
Final Exam
Three Midterm Exams
Problem Sets
Problem Session Quizzes
Quizzes in Lectures (iClickers)
35%
45%
15%
5%
+2%
Are they hard?
Averages on the 3 midterms last year: 80%, 70%, 66%
On the final: 69%
Is there a curve?
yes. in 2010, A > 87%
What to Expect
Comments from Fall 2009
The course was good...it just goes way too fast. There is a lot of material to cover so I understand
the accelerated pace but it almost becomes impossible towards the end of the semester.
Physics I was easier than expected-- definitely a breath of fresh air for a stressed-out pre-med!
Demos were definitely the best part of class
Without Cramster.com the second half of the course would have been an impossible
mountain to overcome. I did learn a lot in this course but if class was not mandatory
due to the clicker questions, I never would have attended.
However, I don't believe that the lectures contributed significantly to my
learning, at least not as much as working practice problems and reading
the textbook did.
7
Learning in PHYS 2010
Study Techniques
•
Read the book
- Keep a pencil in hand, along with scratch paper (& calculator)
-
•
Work example problems.
Work end-of-chapter problems
-
most odd-numbered questions have answers in the back of the book.
focus on completing the problem, correctly. Small mistake = zero
points on the exams
•
Focus on conceptual weaknesses
• Focus on the fundamental concepts, not just the tricky ones
• Take advantage of web resources (example: classic problems may
crop up on study sites)
• Take advantage of office hours
My Office Hours
Tues & Thurs 15:00-18:00, or by appointment. Physics Rm 136.
TA Office Hours
TBD, to be posted on the website.
You can attend office hours for ANY TA from this course
Feedback
email
Feel free to send comments to me directly.
ben@virginia.edu
MasteringPhysics comments
These are sent directly to me, and also logged for the
MasteringPhysics developers
Anonymous feedback
...via UVaCollab site. I have often received useful constructive criticism
in this format.
9
Check Syllabus for reading assignment: (next lecture 2.1-2.5)
Do your reading. Have a pencil in your hand. Do examples. Practice drawing figures.
Register at MasteringPhysics and work the introductory assignment
Course ID
MPNORUM36834 (2)
MPNORUM93099 (3)
Register your iClicker - Go to to UVaCollab, input clicker ID and your email ID
- bring it to every lecture for reading quizzes and concept questions
NO DISCUSSION SECTIONS THIS WEEK
Please exit out the back doors - So the next class can come in the front.
Chapter 1
Introduction to Physics
11
A Quantitative Science
Physics: the study of the fundamental laws of nature
• these laws can be expressed as mathematical equations
• much complexity can arise from relatively simple laws
• this complexity can be analyzed in terms of these simple laws
Physics is a quantitative science, based
on careful measurements.
If you can’t measure it, it isn’t Physics!
Units of Length, Mass, and Time
SI units of length (L), mass (M), time (T)
Length: the meter
Was: one ten-millionth of the distance from the North Pole to the equator
along the line of longitude passing through Greenwich, England.
Now: the distance traveled by light in a vacuum in 1/299,792,458 of a second
Mass: the kilogram
One kilogram is the mass of a particular platinum-iridium cylinder kept at the
International Bureau of Weights and Standards, Sèvres, France.
Time: the second
One second is the time for radiation from a cesium-133 atom to complete
9,192,631,770 oscillation cycles.
Units of Length
Units of Mass
Units of time
Age of Universe
Since dinosaurs
Human life span
Time between heartbeats
Reaction time
For proton to circle LHC
For light to cross a proton
17
10
4x
s
15
2 x 10 s
9
3 x 10 s
0
1 x 10 s
-2
2 x 10 s
9 x 10-5 s
5 x 10-24 s
16
Thinking quantitatively allows us to
describe objects that are outside our
common experience...
... and sometimes find connections we
wouldn’t have seen.
1041 kg
1021 m
10-10 m
10-25 kg
10-14 m
10-27 kg
10-15 m
Dimensions and Units
• Any valid physical formula must be dimensionally
consistent – each term must have the same dimensions;
adding meters to seconds makes no sense.
BUT: factors with different
dimensions can be multiplied
or divided.
From the table:
Distance = velocity × time
Velocity = acceleration × time
Energy = mass × (velocity)2
The density of iron is about 8000 kg / m3 . You have an iron brick with
dimensions 20 cm x 10 cm x 10 cm. What is the mass of the brick ?
Density = [M] / [L3]
Volume= [L3] = 0.2 x 0.1 x 0.1 m3 = 2 x 10-3 m3
Mass = [L3] x [M] / [L3] = (8 x 103 kg / m3) (2 x 10-3 m3)
= 16 kg
Converting Units
Converting feet to meters:
1 in = 0.0254 m (this is an exact conversion factor, the definition
of the inch)
Or:
1 = 0.0254 m / 1 in = 0.0254 m/in = 2.54 cm/in
316 ft = 316 ft x (12 in/ft) x (0.0254 m/in) = 96.3 m
= 316 ft x
1
x
1
= 96.3 m
Note that the units cancel properly – this is the key to using the
conversion factor correctly!
1 mile = 1mile x (5280 ft/mile) x (12 in/ft) x (0.0254 m/in) x (0.001 km/m) = 1.61 km
If something is traveling with a speed of 15 m/s, what is the speed in miles per hour?
Significant Figures
• accuracy of measurements is limited
• significant figures: the number of digits in a quantity
that are known with certainty
• number of significant figures after
addition/subtraction determined by least precise
addend:
65.98
+ 6.3852
72.37
12.9372
- 8.74
4.10
• number of significant figures after multiplication or
division is the number of significant figures in the
least-known quantity
Significant Figures Example
A tortoise travels at 2.51 cm/s for 12.23 s. How far does the tortoise go?
(from a calculator: 2.51 x 12.23 =30.6973)
Answer: 2.51 cm/s × 12.23 s = 30.7 cm (three significant figures)
Units of Length
Scientific Notation and Significant Figures
• Leading or trailing zeroes can make it hard to determine number
of significant figures: 2500, 0.000036
(Each of these has two significant figures)
To specify trailing zeros as significant, we need to make them
“unnecessary”, as in 2500.0)
• Scientific notation writes these as a number between 1 and 10,
multiplied by a power of 10:
2500 = 2.5 × 103
0.000036 = 3.6 x 10-5
We can indicate three significant figures as 2.50x103
(now the trailing zeros mean something!)
Density of big nuclei
density = [Mass]/[Volume] = [M] / [L3]
Neutron Star:
Neutron Star
• 104 m
• 2.7x1030 kg
Lead Nucleus:
Nucleus of Lead-208
• 5x10-15 m
• 2.5x10-25 kg
Order-of-Magnitude Calculations
Why are estimates useful?
•
•
as a check for a detailed calculation – if your answer is very
different from your estimate, you’ve probably made an error
to estimate numbers where a precise calculation cannot be done
Choose useful units, and ignoring the details you don’t need
Example: How many times will your heart beat during your life?
70 times per minute? call it 100.
60 minutes / hour? call it 50
24 hours/day? call it 20
365 days/year? call it 400
130 years? call it 100.
1x102
5x103
1x105
4x107
4x109
4 billion times... if you live to a ripe old age
Scalars and Vectors
Scalar – a numerical value. May be positive or negative.
Examples: temperature, speed, height
Vector – a quantity with both magnitude and direction.
Examples: displacement (e.g., 10 feet north), force, magnetic field
“position” is obviously a vector.
Example: when looking at a 2-dimensional map “2 miles South”
Note: this implicitly has 2 numbers in it: “0 miles East”
Even in 1 dimension, a vector contains extra information compared to a scaler
Example: “10 feet to the left” compared to “10 feet to the right”
or
“-10 feet” compared to “10 ft”
-
+
Basic Geometry and Trigonometry
sin a = A/C = cos b
cos a = B/C = sin b
tan a = A/B = cot b
a
B
C
c=90o
A
b
General properties:
o
a + b + c = 180
2
2
sin a + cos a = 1
Check Syllabus for reading assignment: (next lecture 2.1-2.5)
Do your reading. Have a pencil in your hand. Do examples. Practice drawing figures.
Register at MasteringPhysics and work the introductory assignment
Course ID
MPNORUM36834 (2)
MPNORUM93099 (3)
Register your iClicker - Go to to UVaCollab, input clicker ID and your email ID
- bring it to every lecture for reading quizzes and concept questions
NO DISCUSSION SECTIONS THIS WEEK
Please exit out the back doors - So the next class can come in the front.