Welcome to Principles of Physics I

(PHYS 2010)Professor Blaine Norum

UVaCollab site:-Syllabus-Resources (lecture slides, practice exams, etc.)-Gradebook-Feedback

MasteringPhysics: web interface for assigned problem sets

Note on enrollment: If you are waitlisted and not currently registered in a discussion section: Come see me. In most cases I can sign you in. . Note: you MUST attend the first meeting of your discussion section. Failure to do so may result in your being dropped from the roster and replaced by someone waiting

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Lecture rules

No cell phones.

No laptops EXCEPT in very last row.

Do not interfere with the learning environment

Make space for your fellow students

If you are sick... don’t come to class.

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LecturesFormat • Electronic slides

• Slides will be available after lectures (rarely before)

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

NOTE: I may occasionally miss a class. In this case, your instructor will be another professor with experience in this class.

i>Clickers • Questions in lecture will challenge your conceptual understanding, encourage your engagement and provide me with feedback

• 1 point for participation,

• A second point for correct answer (if scored)

• 2% of your course grade

• You MUST register your i>Clicker for THIS class: go to UVaCollab site.

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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

• 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: -Section 1: MPNORUM25409-Section 2: MPNORUM95999 •use your email/computing ID •Problems: use the online help (“Ask a question”).

There is an introductory assignment (not graded) and also your first assignment (due Friday) available now

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Final Exam 45%Three Midterm Exams 45%Problem Sets 8%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:

Is there a curve? yes. With curve, class average is usually B-/B

Are they hard? Raw averages on the 3 midterms last year: 73%, 77%, 60%On the final: 68%

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Learning in PHYS 2010

TA Office Hours Posted on Collab site.You can attend office hours for ANY TA from this course

My Office Hours

Study Techniques

Tuesday 3-4:30, Thursday 3-4:30, or by appointment. Physics Bldg. Rm 136.

• Read the book- Keep a pencil in hand, along with scratch paper (& calculator)

- Work example problems.

• Work end-of-chapter problems- start with at least one “one dot” problem; a warm-up drill- 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

• 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.

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.

But remember, since it is anonymous I cannot respond to you individually unless you E-mail me directly

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Check Syllabus for reading assignment: (next lecture completes Chapters 2 and 3!)Do your reading. Have a pencil in your hand. Do examples. Practice drawing figures.

Register at MasteringPhysics. look at the introductory assignment (not for credit)work Assignment #1 (for credit, due Tuesday, Sept. 2 at 11:59pm)

Register your iClicker•Go to Collab site, Registration and Course Materials, follow directions•bring it to every lecture for extra credit quizzes and questions

when we finish, Please exit out the back doors - So the next class can come in the front.

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Lecture 1Introduction to Physics

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A Quantitative Science

Physics is a quantitative science, based on careful measurements.

If you can’t measure it, it ain’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

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Science is NOT just a collection of formulae!

Science is a way of understanding the universe – mathematics is the language of science:•Concepts (mass, velocity, momentum, etc.) are the vocabulary•Equations are the grammarTogether, they enable us to describe the wrold around us

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Units of Length, Mass, and Time

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

Time: the secondOne second is the time for radiation from a cesium-133 atom to complete 9,192,631,770 oscillation cycles.

Length: the meterWas: one ten-millionth of the distance from the North Pole to the equatorNow: 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.

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Units of Length

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Units of Mass

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.

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Dimensions and Units

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

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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

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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

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Converting Units

Converting feet to meters:

0.3048 m = 1 ft (this is a conversion factor)

Or: 1 = 0.3048 m / 1 ft

316 ft × (0.3048 m / 1.0 ft) = 96.3 m

Note that the units cancel properly – this is the key to using the conversion factor correctly!

There are 1.6 km to 1 mile.

If something is traveling with a speed of 15 m/s, what is the speed in miles per hour?

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• accuracy of measurements is limited

• significant figures: the number of digits in a quantity that are known with certainty

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

Significant Figures

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

Significant Figures Example

(from a calculator: 2.51 x 12.23 =30.6973 cm)

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

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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)

In this case, the trailing zeros are necessary. They are only clearly significant if they are “necessary”, 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!)

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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 40080 years? 130 years? call it 100.

1x102

5x103

1x105

4x107 4x109

4 billion times... if you live to a ripe old age

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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”

“position” corresponds to “displacement”, a vector.

length of travel is “distance”, a scaler

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Position, Distance, and DisplacementBefore describing motion, you must set up a coordinate system – define an origin and a positive direction.

The distance is the total length of travel; if you drive from your house to the grocery store and back, you have covered a distance of 8.6 mi. Your net displacement is zero.

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Position, Distance, and Displacement

If you drive from your house to the grocery store and then to your friend’s house, your displacement is -2.1 mi and the distance you have traveled is 10.7 mi. 28

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Average SpeedThe average speed is defined as the distance traveled divided by the time the trip took:

Average speed = distance / elapsed time

If you drive from your house to the grocery store and then to your friend’s house, your displacement is -2.1 mi and the distance you have traveled is 10.7 mi. The trip takes 30 minutes (with traffic and lights).

What is your average speed?

10.7 miles

0.5 hourssav =

= 21.4 miles/hr

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Average VelocityAverage velocity = displacement / elapsed time

If you return to your starting point, your average velocity is zero.

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Check Syllabus for reading assignment: (next lecture completes Chapters 2 and 3!)Do your reading.

Register at MasteringPhysics. work Assignment #1 (for credit, due Tuesday, Sept. 2 at 11:59pm)

Register your iClicker •Go to Collab site, got to Registration and Course Materials and follow instructions•Bring it to every lecture for extra credit quizzes and questions

Please exit out the back doors - So the next class can come in the front.