Physics 1501: Lecture 1, Pg 1 Physics 1501, Sections: 1 – 7 “Physics for Engineers - I”...

Physics 1501: Lecture 1, Pg 1

Physics 1501, Sections: 1 – 7 Physics 1501, Sections: 1 – 7 ““Physics for Engineers - IPhysics for Engineers - I””

Professor Robin CôtéProfessor Robin Côté

Lecture 1Lecture 1Agenda for TodayAgenda for Today

Topic – Doing PhysicsTopic – Doing Physics Realms of Physics Measurement and Units Dimensional Analysis Significant digits Strategies for Learning (IDEA)

Course IntroductionCourse Introduction Scope of the courseScope of the course Structure of the courseStructure of the course what you have to dowhat you have to do


Course InfoCourse Info

Course has several components:

Lecture: (me talking, demos and Active learning).

Homework Sets: problems from the book.

Tests: two midterms and a final.

» Questions on tests will look like those we do in the rest of the class; in homework and during lectures.

» No surprises

Office hours: to answer additional questions

Labs: (group exploration of physical phenomena).


How to do well in the course ?How to do well in the course ? FINAL GRADE WILL BE MADE OF:

» 2 Midterms 30%

» Final Exam 25%

» Homeworks 20%

» Labs 25%

• Remember:• if you miss 1 HW (out of ~10 given during the semester), you miss 2% of the final score !

• if you miss more than one LAB => incomplete


AnnouncementsAnnouncements Most of the info about the class will be posted on:

www.phys.uconn.edu/~rcote

» lecture notes (.ppt and .pdf formats)

» homework assignments

» Syllabus Look at First Day of Class .for details

Follow the link to 1501 – Sec. 1-7

• Labs start during the week of Sept. 12 (check with your TA)


• Homeworks will be posted on Mastering Physics

www.masteringphysics.com

Register for MasteringPhysics

Course ID: MPCOTE94952

• HW will be due usually Fri. mornings (8:00 am)

• No Late HW accepted

HELP:• Become familiar with the Physics Resource Center for help with

problem sets. Room P207, time posted on the door.


Lecture OrganizationLecture Organization Three main components:Three main components:

Lecturer discusses class material» Topics from text

Lecturer does demos/expts when possible» Its not truth unless it makes a verifiable

prediction !

You and I will interact with conceptual“Active Learning” problems.» Usually two or three per lecture

Active Figures » To illustrate concepts

ActAct


Doing PhysicsDoing Physics At its heart, physics is about the study of

everything! Studying physics helps us gain insight into why

things are the way they are at their most fundamental level.

Physics is the search for the answer to the fundamental question: “why?” in the physical realities governing our world.It explains the natural phenomena around us.


Realms of PhysicsRealms of Physics Studying “everything” is a bit of a challenge

Divide physics into different areas of study:


Scope of Physics 1501Scope of Physics 1501

Classical Mechanics:Classical Mechanics:Mechanics: Mechanics: How and why things work.

motion, balance, energy, vibrationsClassical: Classical:

» Not too fast (v << c)

» Not too small (d >> atom)

Most everyday situations can be described in these Most everyday situations can be described in these terms.terms.

Path of baseball Orbit of planets Vibrations of a piano wire


Measurements and UnitsMeasurements and Units Physics (science) provides detailed descriptions:

“That car moves really fast,” or “I can run a long way,” are subjective and arbitrary.

All of our descriptions (measurements) must be objectively quantified – i.e. standardized!

All things in classical mechanics can be expressed in terms of the fundamental quantities:fundamental quantities:Length LMass MTime T

Some examples of more complicated quantities: Speed has the quantity of L / T (i.e. miles per hour). Acceleration has the quantity of L/T2. Force has the quantity of ML / T2 (as you will learn).


UnitsUnits

SI (Système International) Units:SI (Système International) Units:mks: L = meters (m), M = kilograms (kg), T = seconds (s)

British Units:British Units:L = inches, feet, miles, M = slugs (pounds), T = seconds

We will use mostly SI units, but you may run across some problems using British units. You should know how to convert back & forth.


Measurements and UnitsMeasurements and Units

LengthThe meter is presently defined as “the length of the

path traveled by light in a vacuum during a time interval of 1/299,792,458 of a second.”

Operational definition: measurement standard based on a laboratory procedure – can be reproduced “easily”


LengthLength::

DistanceDistance Length (m)Length (m)Radius of Visible Universe 1 x 1026

To Andromeda Galaxy 2 x 1022

To nearest star 4 x 1016

Earth to Sun 1.5 x 1011

Radius of EarthSears Tower 4.5 x 102

Football Field 1.0 x 102

Tall person 2 x 100

Thickness of paperWavelength of blue lightDiameter of hydrogen atomDiameter of proton 1 x 10-15

6.4 x 106

1 x 10-4

4 x 10-7

1 x 10-10



TimeThe second was once defined by the rotation of the

earth – but this rotation is not constant!In 1967, the second was given an operational

definition based on the transitions of the cesium atom.The second is currently defined as “the duration of

9,192,631,770 periods of the radiation corresponding to the transition between the two hyperfine levels of the ground state of the cesium-133 atom”


Time:Time:

IntervalInterval Time (s)Time (s)Age of Universe 5 x 1017

Age of Grand Canyon 3 x 1014

Avg age of college student 6.3 x 108

One yearOne hourLight travel from Earth to MoonOne cycle of guitar A string 2 x 10-3

One cycle of FM radio wave 6 x 10-8

One cycle of visible lightTime for light to cross a proton 1 x 10-24

3.2 x 107

3.6 x 103

1.3 x 100

1 x 10-15



MassThe least “convenient” of the defined units.The kilogram is defined by an object – not by an

experiment reproducible in laboratories.At the moment, the prototype kilogram is made of a

special platinum-iridium alloy that does not corrode.Work is in progress to define the kilogram based on

the mass of a single atom – this would lead to an operational definition


Mass:Mass:

ObjectObject Mass (kg)Mass (kg)visible universe ~ 1052

Milky Way galaxy 7 x 1041

Sun 2 x 1030

Earth 6 x 1024

Boeing 747 4 x 105

Car 1 x 103

Student 7 x 101

Dust particle 1 x 10-9

Bacterium 1 x 10-15

Proton 2 x 10-27

Electron 9 x 10-31



Other SI unitsThroughout this course and the second course in the

sequence, we will meet more SI unitsSome will be unique, e.g.

» ampère (A): measures electric current

» kelvin (K): measures temperature

» radian (rad): measures anglesSome will be combinations of the “main three,” e.g.

» Newton (N = kg·m/s2): measures force

» Pascal (Pa = kg/m·s2): measures pressure UNITS MATTER!!


Some Prefixes for Power of TenSome Prefixes for Power of Ten

PowerPower PrefixPrefix Abbreviation

103 kilo k106 mega M109 giga G1012 tera T1015 peta P1018 exa E

10-18 atto a

10-15 femto f

10-12 pico p

10-9 nano n

10-6 micro 10-3 milli m



Other unit systemsUnited States still uses “English system:”

» Inches, feet, yards, pounds, gallons, etc.For most problems in this course, we will use SI units.Unless otherwise specified, assume SI units.

Changing unitsBeing able to convert from one system to another is an

important skill to have.There is always a conversion factor, that allows us to

change from one unit to another


Converting between different Converting between different systems of unitssystems of units

Useful Conversion factors:1 inch = 2.54 cm1 m = 3.28 ft1 mile = 5280 ft 1 mile = 1.61 km

Example: convert miles per hour to meters per second:


Lecture 1, Lecture 1, ACT 1ACT 1 Converting between different systems of unitsConverting between different systems of units

When on travel in Europe you rent a small car which consumes 6 liters of gasoline per 100 km. What is the MPG of the car ?

Useful Conversion factors:1 gallon = 4 liters1 mile = 1.61 km

SolutionSolution

= 41 MPG !


Working with NumbersWorking with Numbers

Scientific NotationOften times in physics, we deal with numbers that are

really large (distance from the earth to the sun) or numbers that are really small (distance of an electron from the nucleus).

To handle such numbers, we use scientific notation:

» Numbers are expressed as a “reasonable number” multiplied by a factor of 10

Examples:

» 51985 = 5.1985 × 104

» 67,860,000,000 = 6.786 × 1010

» .0000239 = 2.39 × 10-5


Working with NumbersWorking with Numbers

Significant FiguresThe precision of our measurement is implied

in the amount of significant figures used (the “reasonable number” mentioned on previous slide).

In this age of calculators and computers, it is easy to lose sight of which digits are significant and which are not.


Order of Magnitude Calculations / EstimatesOrder of Magnitude Calculations / Estimates EarthEarth’’s radius ?s radius ?

Need to know something from your experience:Flying from NYC to SF one accumulates ~ 3,500 milesNYC to SF spans about 1/6 of the Earth’s circumferenceSo, the Earth’s circumference L = 3,500 x 6 ~ 20,000 miSince circumference of a circle is : L = 2 r Estimate of Earth radius :

3x103 mi = 3x103 x 1.61 km ~ 5x103 km = 5x106 m


This is a very important tool to check your workIt’s also very easy!

Example:Example:Doing a problem you get the answer for distance d = v t 2 ( velocity x time2 )

Quantity on left side = LQuantity on right side = L / T x T2 = L x T

Left units and right units donLeft units and right units don’’t match, so answer must be t match, so answer must be wrong !!wrong !!

Dimensional Analysis Dimensional Analysis


Lecture 1, Lecture 1, ACT 2ACT 2

There is a famous Einstein's equation connecting energy and mass (relativistic). Using dimensional analysis find which is the correct form of this equation :

Solution -> (b)Solution -> (b)

Note : c is speed of light (L/T)E is energy (M L2 / T2)

(a)(a) (b)(b) (c)(c)


Significant FiguresSignificant Figures The number of digits that matter in a measurement or calculation. When writing a number, all non-zero digits are significant. Zeros may or may not be significant.

those used to position the decimal point are not significant. those used to position powers of ten ordinals may or may not be

significant.

in scientific notation all digits are significant Examples:

2 1 sig fig40 ambiguous, could be 1 or 2 sig figs4.0 x 101 2 sig figs0.0031 2 sig figs3.03 3 sig figs


Significant FiguresSignificant Figures

When multiplying or dividing, the answer should have the same number of significant figures as the least accurate of the quantities in the calculation.

When adding or subtracting, the number of digits to the right of the decimal point should equal that of the term in the sum or difference that has the smallest number of digits to the right of the decimal point.

Examples:2 x 3.1 = 63.1 + 0.004 = 3.14.0 x 101 2.04 x 102 = 1.6 X 10-1


Strategies for Learning PhysicsStrategies for Learning Physics

Most of the ideas and concepts you will learn in this class are not inherently difficult.

The challenges of this class will be in the problem solving: understanding what exactly is being asked of you and figuring out how you can derive the solution.

Your textbook introduces a problem-solving strategy named IDEA (Interpret Develop Evaluate and Assess).More later

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