Welcome to Principles of Physics I

(PHYS 2010)

Lecture 002 - 11:00-12:15 TuTh 003 - 12:30-13:45 TuTh

http://people.virginia.edu/~kdp2c/PHYS2010_Fall2010/index.html

Course website:

Professor Blaine Norum

(linked from UVa Collab site)

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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)

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.

LecturesFormat • Electronic slides

• Slides will be available after lectures (rarely before)

• Frequent demos to build intuition, relate to the real world, and encourage engagement

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

• Many more “participation” questions throughout class (credit for any answer)

• 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.

5

Mastering PhysicsA web-based homework system

• Instantaneous feedback

• Multiple attempts at problem solving (guessing discouraged)

• Hints, tutorials, and other support

• Excellent feedback to instructors

• Well 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.

Final Exam 35%Three Midterm Exams 45%Problem Sets 15%Problem Session Quizzes 5%Quizzes in Lectures (iClickers) +2%

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 203Section 3: Thursday, December 15 @ 14:00-17:00, Room 203

Is there a curve? yes. in 2010, A > 87%

Are they hard? Averages on the 3 midterms last year: 80%, 70%, 66%On the final: 69%

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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.

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.

What to ExpectComments from Fall 2009

Learning in PHYS 2010

TA Office Hours TBD, to be posted on the website. You can attend office hours for ANY TA from this course

My Office Hours

Study Techniques

Tues & Thurs 15:00-18:00, or by appointment. Physics Rm 136.

• 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

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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.

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 assignmentCourse 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.

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Chapter 1Introduction to Physics

A Quantitative Science

Physics is a quantitative science, based on careful measurements.

If you can’t measure it, it isn’t Physics!

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

Units of Length, Mass, and Time

SI units of length (L), mass (M), time (T)

Length: the meterWas: 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 kilogramOne kilogram is the mass of a particular platinum-iridium cylinder kept at the International Bureau of Weights and Standards, Sèvres, France.

Time: the secondOne 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 4 x 1017 s

Since dinosaurs 2 x 1015 s

Human life span 3 x 109 s

Time between heartbeats 1 x 100 s

Reaction time 2 x 10-2 s

For proton to circle LHC 9 x 10-5 s

For light to cross a proton 5 x 10-24 s

16

1021 m1041 kg

10-10 m

10-14 m

10-15 m10-27 kg

10-25 kg

Thinking quantitatively allows us to describe objects that are outside our common experience...

... and sometimes find connections we wouldn’t have seen.

Dimensions and Units

BUT: factors with different dimensions can be multiplied or divided.

From the table:

Distance = velocity × time

Velocity = acceleration × time

Energy = mass × (velocity)2

• Any valid physical formula must be dimensionally consistent – each term must have the same dimensions; adding meters to seconds makes no sense.

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?

• 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 12.9372

+ 6.3852 - 8.74

72.37 4.10

• number of significant figures after multiplication or division is the number of significant figures in the least-known quantity

Significant Figures

A tortoise travels at 2.51 cm/s for 12.23 s. How far does the tortoise go?

Answer: 2.51 cm/s × 12.23 s = 30.7 cm (three significant figures)

Significant Figures Example

(from a calculator: 2.51 x 12.23 =30.6973)

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

Nucleus of Lead-208• 5x10-15 m• 2.5x10-25 kg

density = [Mass]/[Volume] = [M] / [L3]

Neutron Star:

Lead Nucleus:

Neutron Star• 104 m• 2.7x1030 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 5024 hours/day? call it 20365 days/year? call it 400130 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

a

B C

c=90o b

A

sin a = A/C = cos bcos a = B/C = sin btan a = A/B = cot b

General properties: a + b + c = 180o

sin2a + cos2a = 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 assignmentCourse 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.