Physics 1501: Lecture 1, Pg 1 Physics 1501, Sections: 1 – 7 “Physics for Engineers - I” Professor Robin Côté Lecture 1 Agenda for Today l Topic – Doing Physics ç Realms of Physics ç Measurement and Units ç Dimensional Analysis ç Significant digits ç Strategies for Learning (IDEA) l Course Introduction ç Scope of the course ç Structure of the course ç what you have to do

Physics 1501: Lecture 1, Pg 2 Course Info l Course has several components: çLecture: (me talking, demos and Active learning). çHomework Sets: problems from the book. çTests: 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 çOffice hours: to answer additional questions çLabs: (group exploration of physical phenomena).

Physics 1501: Lecture 1, Pg 3 How to do well in the course ? l 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

Physics 1501: Lecture 1, Pg 4 Announcements l Most of the info about the class will be posted on: ç »lecture notes (.ppt and.pdf formats) »homework assignments »SyllabusSyllabus n Look at First Day of Class.for detailsFirst Day of Class çFollow the link to 1501 – Sec – Sec. 1-7 Labs start during the week of Sept. 12 (check with your TA)

Physics 1501: Lecture 1, Pg 5 Homeworks will be posted on Mastering Physics 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.

Physics 1501: Lecture 1, Pg 6 Lecture Organization l Three main components: çLecturer discusses class material »Topics from text çLecturer does demos/expts when possible »Its not truth unless it makes a verifiable prediction ! çYou and I will interact with conceptual “Active Learning” problems. »Usually two or three per lecture çActive Figures »To illustrate concepts Act

Physics 1501: Lecture 1, Pg 7 Doing Physics l At its heart, physics is about the study of everything! l Studying physics helps us gain insight into why things are the way they are at their most fundamental level. l Physics is the search for the answer to the fundamental question: “why?” in the physical realities governing our world. çIt explains the natural phenomena around us.

Physics 1501: Lecture 1, Pg 8 Realms of Physics l Studying “everything” is a bit of a challenge çDivide physics into different areas of study:

Physics 1501: Lecture 1, Pg 9 Scope of Physics 1501 l Classical Mechanics: çMechanics: çMechanics: How and why things work. motion, balance, energy, vibrations çClassical: »Not too fast (v << c) »Not too small (d >> atom) l Most everyday situations can be described in these terms. ç Path of baseball ç Orbit of planets ç Vibrations of a piano wire

Physics 1501: Lecture 1, Pg 10 Measurements and Units l Physics (science) provides detailed descriptions: ç“That car moves really fast,” or “I can run a long way,” are subjective and arbitrary. l All of our descriptions (measurements) must be objectively quantified – i.e. standardized! fundamental quantities: l All things in classical mechanics can be expressed in terms of the fundamental quantities: çLength L çMass M çTime T l Some examples of more complicated quantities: ç Speed has the quantity of L / T (i.e. miles per hour). ç Acceleration has the quantity of L/T 2. ç Force has the quantity of ML / T 2 (as you will learn).

Physics 1501: Lecture 1, Pg 11 Units l SI (Système International) Units: çmks: L = meters (m), M = kilograms (kg), T = seconds (s) l British Units: çL = inches, feet, miles, M = slugs (pounds), T = seconds l We will use mostly SI units, but you may run across some problems using British units. You should know how to convert back & forth.

Physics 1501: Lecture 1, Pg 12 Measurements and Units l Length çThe 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.” çOperational definition: measurement standard based on a laboratory procedure – can be reproduced “easily”

Physics 1501: Lecture 1, Pg 13 Length : DistanceLength (m) Distance Length (m) Radius of Visible Universe 1 x To Andromeda Galaxy 2 x To nearest star 4 x Earth to Sun 1.5 x Radius of Earth Sears Tower 4.5 x 10 2 Football Field1.0 x 10 2 Tall person 2 x 10 0 Thickness of paper Wavelength of blue light Diameter of hydrogen atom Diameter of proton 1 x x x x x

Physics 1501: Lecture 1, Pg 14 Measurements and Units l Time çThe second was once defined by the rotation of the earth – but this rotation is not constant! çIn 1967, the second was given an operational definition based on the transitions of the cesium atom. çThe 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”

Physics 1501: Lecture 1, Pg 15 Time: IntervalTime (s) Interval Time (s) Age of Universe 5 x Age of Grand Canyon 3 x Avg age of college student6.3 x 10 8 One year One hour Light travel from Earth to Moon One cycle of guitar A string 2 x One cycle of FM radio wave 6 x One cycle of visible light Time for light to cross a proton 1 x x x x x

Physics 1501: Lecture 1, Pg 16 Measurements and Units l Mass çThe least “convenient” of the defined units. çThe kilogram is defined by an object – not by an experiment reproducible in laboratories. çAt the moment, the prototype kilogram is made of a special platinum-iridium alloy that does not corrode. çWork is in progress to define the kilogram based on the mass of a single atom – this would lead to an operational definition

Physics 1501: Lecture 1, Pg 17 Mass: ObjectMass (kg) Object Mass (kg) visible universe ~ Milky Way galaxy 7 x Sun 2 x Earth 6 x Boeing x 10 5 Car 1 x 10 3 Student 7 x 10 1 Dust particle 1 x Bacterium 1 x Proton 2 x Electron 9 x

Physics 1501: Lecture 1, Pg 18 Measurements and Units l Other SI units çThroughout this course and the second course in the sequence, we will meet more SI units çSome will be unique, e.g. »ampère (A): measures electric current »kelvin (K): measures temperature »radian (rad): measures angles çSome will be combinations of the “main three,” e.g. »Newton (N = kg·m/s 2 ): measures force »Pascal (Pa = kg/m·s 2 ): measures pressure l UNITS MATTER!!

Physics 1501: Lecture 1, Pg 19 Some Prefixes for Power of Ten PowerPrefix PowerPrefixAbbreviation 10 3 kilok 10 6 megaM 10 9 gigaG teraT petaP exaE attoa femtof picop nanon micro  millim

Physics 1501: Lecture 1, Pg 20 Measurements and Units l Other unit systems çUnited States still uses “English system:” »Inches, feet, yards, pounds, gallons, etc. çFor most problems in this course, we will use SI units. çUnless otherwise specified, assume SI units. l Changing units çBeing able to convert from one system to another is an important skill to have. çThere is always a conversion factor, that allows us to change from one unit to another

Physics 1501: Lecture 1, Pg 21 Converting between different systems of units l Useful Conversion factors: ç1 inch= 2.54 cm ç1 m = 3.28 ft ç1 mile= 5280 ft ç1 mile = 1.61 km l Example: convert miles per hour to meters per second:

Physics 1501: Lecture 1, Pg 22 Lecture 1, ACT 1 Converting between different systems of units l 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 ? l Useful Conversion factors: ç1 gallon= 4 liters ç1 mile= 1.61 km Solution = 41 MPG !

Physics 1501: Lecture 1, Pg 23 Working with Numbers l Scientific Notation çOften 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). çTo handle such numbers, we use scientific notation: »Numbers are expressed as a “reasonable number” multiplied by a factor of 10 çExamples: »51985 = × 10 4 »67,860,000,000 = × » = 2.39 × 10 -5

Physics 1501: Lecture 1, Pg 24 Working with Numbers l Significant Figures çThe precision of our measurement is implied in the amount of significant figures used (the “reasonable number” mentioned on previous slide). çIn this age of calculators and computers, it is easy to lose sight of which digits are significant and which are not.

Physics 1501: Lecture 1, Pg 25 Order of Magnitude Calculations / Estimates Earth’s radius ? l Need to know something from your experience: çFlying from NYC to SF one accumulates ~ 3,500 miles çNYC to SF spans about 1/6 of the Earth’s circumference çSo, the Earth’s circumference L = 3,500 x 6 ~ 20,000 mi çSince circumference of a circle is : L = 2  r çEstimate of Earth radius : 3x10 3 mi = 3x10 3 x 1.61 km ~ 5x10 3 km = 5x10 6 m

Physics 1501: Lecture 1, Pg 26 l This is a very important tool to check your work çIt’s also very easy! l Example: Doing a problem you get the answer for distance d = v t 2 ( velocity x time 2 ) Quantity on left side = L Quantity on right side = L / T x T 2 = L x T l Left units and right units don’t match, so answer must be wrong !! Dimensional Analysis

Physics 1501: Lecture 1, Pg 27 Lecture 1, ACT 2 l 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) l Note : ç c is speed of light (L/T) çE is energy (M L 2 / T 2 ) (a)(b)(c)

Physics 1501: Lecture 1, Pg 28 Significant Figures l The number of digits that matter in a measurement or calculation. l When writing a number, all non-zero digits are significant. l Zeros may or may not be significant. çthose used to position the decimal point are not significant. çthose used to position powers of ten ordinals may or may not be significant. l in scientific notation all digits are significant l Examples: ç21 sig fig ç40ambiguous, could be 1 or 2 sig figs ç4.0 x sig figs ç sig figs ç3.033 sig figs

Physics 1501: Lecture 1, Pg 29 Significant Figures l When multiplying or dividing, the answer should have the same number of significant figures as the least accurate of the quantities in the calculation. l 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. l Examples: ç2 x 3.1 = 6 ç = 3.1 ç4.0 x 10 1  2.04 x 10 2 = 1.6 X 10 -1

Physics 1501: Lecture 1, Pg 30 Strategies for Learning Physics l Most of the ideas and concepts you will learn in this class are not inherently difficult. l 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. l Your textbook introduces a problem-solving strategy named IDEA (Interpret Develop Evaluate and Assess). çMore later