P1_Introduction

P1_Introduction - PHY 101 PHY Major Concepts in Physics...

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Unformatted text preview: PHY 101 PHY Major Concepts in Physics Prof Stefan Ballmer Syllabus Syllabus Available online • tinyurl.com/SUphy101 • or blackboard.syr.edu Highlights 3 Exams Sept. 28, Oct. 24, Nov 16 + Final Dec 15 =2 exams NO MAKE­UPS TEXTBOOK TEXTBOOK College Physics 2nd custom edition Available in SU book store Includes access to • e­book • Mastering Physics (homework) Studios (labs) & Homework Studios Studios (labs) • Begin week of Sept. 12. • 9 Lab­ Studios + 1 make­up Homework every week. • Online (Mastering Physics) • Your book package includes access codes. • Please register ASAP! Registering for Homework Got to http://www.masteringphysics.com Get an account, use your access code Registering for Homework You need to enter the course ID: • SUPHY101FALL2011 • (available on syllabus) Registering for Homework As well as your SU NetID: Registering for Homework The first homework is a practice at using Mastering Physics Make sure you know how the web site works before next week’s assignment! The web site will not accept late homework! Do not wait until the last minute in case you have technical problems! Grades Grades 4 best exams 400 pts Studio 135 pts HW 65 pts Total Pass 600 pts 360 pts (60%) Checking Understanding The answer is 42. What is the answer? A. 10 B. 12 C. 42 D. 99 Slide 1­19 There is more to lectures than the power point slides! Participate! Enjoy the journey! The scope of physics The “Physics is the study of your world and the world and universe around you.” (S. Holzner “Physics for Dummies”) familiar The scope of physics The “Physics is the study of your world and the world and universe around you.” (S. Holzner “Physics for Dummies”) Mars Rover Not so familiar Laws of Nature are universal The scope of physics The “Physics is the study of your world and the world and universe around you.” (S. Holzner “Physics for Dummies”) Atomic Force Microscope image of Pentacene Nature Methods 6, 792 (2009) Not familiar Laws of Nature need to span many orders of magnitude! Powers of Ten The scope of physics The Reality is complicated! • We will use models to describe nature (simplification) How much simplification? • • • Depends on what we are interested in Model has to predict nature Mathematical models have proven to be very powerful, but they are still models. SCIENTIFIC NOTATION SCIENTIFIC How Far is a Star? How The nearest star, α Centauri, is 44 Quadrillion meters or 44,000,000,000,000,000 meters away What does this mean? How can we keep track of all those zeros? 0 is important!! Example Example The radius of the sun is 700,000 km. Write as 7.0× 105 km. When properly written this number will be between 1.0 and 10.0 Example: The radius of a hydrogen atom is 0.0000000000529 m. This is more easily written as 5.29× 10­11 m. Arithmetic with Scientific Notation Arithmetic Multiplication ­> Add Exponents e.g. 107 x 103 = 107+3 = 1010 Division ­> Subtract exponents e.g. 107/103 = 107­3 =104 Negative powers are inverses e.g. 10­3 = 1/103 10 x 10­1 =10/10 =1 = 101­1= 100 Significant Figures Significant Find the value of 6.49m divided by 5.1037s Calculator gives 1.271626467 ! Too many figures. FALSE Accuracy. Round off! Only 3 significant figures. Why? 1.27m/s But don’t round telephone numbers! Units: The SI system We will mostly use the “Système international d'unités “ (SI) Basic units: • Length: • Time: • Mass: •… Derived units: • Speed: •… Meter (m) Second (s) Kilogram (kg) (NOT g…) Meters/Second (m/s) Units: The SI system Some other units • 1 foot = 0.3048 m Mile, yard, inch, etc… ~ 1 kg • 2.2 lb • Minute, hour, day, etc… •… ESTIMATION Estimate the number of times a human heart beats during its lifetime. Estimate - a typical heart beats ~60 times per minute: 60 beats 60 minutes 24 hours 365 days 75 years ÷ ÷ 1day ÷ 1 year ÷ 1 lifetime ÷ ÷ ÷ 1 minute 1 hour 2.4 x 109 beats/lifetime Life in terms of heart beats Life Almost all mammals from tiny shrews to huge elephants live about a billion heartbeats! Elephant shrew Elephant 1 Representing motion 1 Representing motion The world around us always changes. Some things move fast… • E.g. hummingbird Others change slowly… • E.g. mountains Describing motion Describing How can we describe motion? • E.g. of a “hover puck” or a “fan car” We need the concepts of Time • I can’t tell you what it is • But I can show you how to measure it (pendulum, metronome, clock) Describing motion Describing This is a Motion Diagram Motion­The Particle Model A simplifying model in which we treat the object as if all its mass were concentrated at a single point. This model helps us concentrate on the overall motion of the object. Slide 1­16 Position and Time The position of an object is located along a coordinate system. At each time t, the object is at some particular position. We are free to choose the origin of time (i.e., when t = 0). Slide 1­17 Displacement The change in the position of an object as it moves from initial position xi to final position xf is its displacement ∆x = xf – xi. Slide 1­18 Checking Understanding Maria is at position x = 23 m. She then undergoes a displacement ∆x = –50 m. What is her final position? A. –27 m B. –50 m C. 23 m D. 73 m Slide 1­19 Speed of a Moving Object O O O O O O O O O O Slide 1­25 Speed of a Moving Object 40 ft The car moves 40 ft in 1 s. Its speed is = 40 . 1 s ft s 20 ft ft The bike moves 20 ft in 1 s. Its speed is = 20 . 1 s s Slide 1­25 Checking Understanding Two runners jog along a track. The positions are shown at 1 s time intervals. Which runner is moving faster? C) same speed D) Not enough information Slide 1­21 Velocity of a Moving Object Slide 1­26 Vectors A quantity that requires both a magnitude (or size) and a direction can be represented by a vector. Graphically, we represent a vector by an arrow. The velocity of this car is 100 m/s (magnitude) to the left (direction). This boy pushes on his friend with a force of 25 N to the right. Slide 1­32 Displacement is a vector Velocity is a vector Displacement Vectors A displacement vector starts at an object’s initial position and ends at its final position. It doesn’t matter what the object did in between these two positions. In motion diagrams, the displacement vectors span successive particle positions. Slide 1­33 Vectors versus scalars: A scalar is just a number (no direction). The mass of an object is an example of a scalar quantity. Volume is a scalar A vector is a quantity that has both a magnitude and a direction. Velocity is an example of a vector quantity. Force is a vector Vectors Vectors To graphically represent a vector, draw a directed line segment. The length of the line can be used to represent the vector’s length or magnitude. Notation: Scalar: m (not bold face; no arrow) Vector: v F or F The magnitude of a vector: v F or F or F . The direction of vector might be “35° south of east”; “20° above the +x-axis”; etc…. Adding vectors To add vectors graphically they must be placed “tip to tail”. The result (F1 + F2) points from the tail of the first vector to the tip of the second vector. F1 For collinear vectors: F2 Fnet ? F1 F2 Fnet ? Adding Vectors Adding Length b Length a c Θ b a + b = c 2 + b2 = c2 a Tan θ =b/a Adding Vectors Adding Can also add Same result as before Components Components a=c cosθ c b θ a b=c sinθ a2 +b2 = c2 Adding Vectors: arbitratry Adding Length a Length b Example: Crosswind Landing Velocity of aircraft through air 50 m/s Cross wind 10 m/s Velocity over ground = ? Example: Crosswind Landing Where does the wind come from? A) C) no wind D) not enough information B) ...
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This note was uploaded on 02/15/2012 for the course PHYSICS 200 taught by Professor Staff during the Fall '11 term at Syracuse.

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