Welcome to Physics 101 Lecture 01 Introduction to

Welcome to Physics 101! Lecture 01: Introduction to Forces “[in high school] all we did was make trebuchets, pasta towers, and toothpick boats. It was fun, but we didn’t learn much. ” “I am very excited about taking Physics 101!” “lectures seem fun with all the experiments” “Nervous” “Anxious” “Apprehensive” “I have to take it to graduate… crap” “…will be a change from my biology based classes. ” http: //online. physics. uiuc. edu/courses/phys 101/spring 10/index. html Physics 101: Lecture 1, Pg 1

Meet the Lecturer l Charles Gammie gammie@illinois. edu l Office Hours Monday 10 -11 271 Loomis l Research èAstrophysics – black holes! l P 101 is one of my favorite courses! • http: //online. physics. uiuc. edu/courses/phys 101/spring 10/index. html Physics 101: Lecture 1, Pg 2

Course Format (upward) Spiral Learning Lecture Preflights l Lecture Participation l Homework l Lab l Discussion l clickers 25 25 100 150 100 èquizzes; drop lowest 1 Hour Exams (3 x 100) l Final Exam l 300 1000 Physics 101: Lecture 1, Pg 3

Grading Scale 950 -1000 l 920 -949 l 900 -919 l 880 -899 l 860 -879 l 835 -859 l A+ A AB+ B B- 810 -834 l 780 -809 l 750 -779 l 720 -749 l 690 -719 l 610 -689 l <610 l C+ C CD+ D DF “Let’s get a good grade…” Physics 101: Lecture 1, Pg 4

Reading & Lecture Preflight l Need to complete Pre. Lecture for Preflight l Answer preflights 25/1000 points èDue 6: 00 am day of lecture. è 1 points for honest attempt at preflight (lose points for nonsense – and I read these!). èNo EX, 28 Lectures can miss three and still get all 25 points. l Everyone gets 1 point for today! Physics 101: Lecture 1, Pg 5

P 101 Lectures l Participation is key! “I’m looking forward to a fun … semester” èCome to lecture prepared! è 1 point for each lecture using iclicker » No EX, 28 Lectures can miss three and still get all 25 points. » Available at bookstore---register using link on web page. l Not everything you need for exams! èConcepts, Connections, Motivation èComprehensive Text èCalculations Homework + Discussion èHands-On Lab l Taking Notes èLecture notes available for lecture. èSome key pieces for you to fill in. Physics 101: Lecture 1, Pg 6

P 101 Homework l All web based, immediate feedback l 100% if done before 6: 00 am deadline l 90% credit on unfinished parts until following Tuesday l 0% after that l Always keep 5 significant figures! l First two are due Tues Feb 2 ! Physics 101: Lecture 1, Pg 7

P 101 Labs “I am excited to see what kind of labs we will be doing. ” l Director: Professor Robert Clegg l First is Today! l No “dropped” labs…. . Don’t miss one! Physics 101: Lecture 01, Pg 8

Discussion Sections l Director: Professor Yoshi Oono l Start: yesterday! l Quiz during last 20 minutes of section l 10 minutes late l First section: math review, dimensional analysis. Physics 101: Lecture 1, Pg 9

Physics Philosophy “I do better in classes that require memorization. ” l Physics is DIFFERENT l Describe large number of “complicated” observations with a few simple ideas l Exams don’t have same problems, but do have same IDEAS Physics 101: Lecture 1, Pg 10

Newton’s Laws of Motion 1. If the sum of all external forces on an object is zero, then its speed and direction will not change. Inertia 2. If a nonzero net force is applied to an object its motion will change F= ma 3. In an interaction between two objects, the forces that each exerts on the other are equal in magnitude and opposite in direction. Physics 101: Lecture 1, Pg 11

Forces in P 101 l Non-Contact ---- Gravity (|F| = G m M/r 2 ) èG = 6. 7 x 10 -11 m 3 / (kg s 2) èEarth: Mass = 6 x 1024 kg, radius = 6. 4 x 106 m. l Contact (fundamentally E+M) èNormal: Perpendicular to surface èFriction: Parallel to surface èAnything touching the object » Rope: Tension » Spring F = -kx Physics 101: Lecture 1, Pg 12

Example Weight of Object l Calculate the gravitational force on a 3 kg book held 1 meter above the surface of the earth. |F| = G M m / r 2 = (6. 7 x 10 -11 m 3 / (kg s 2)) (6 x 1024 kg) (3 kg)/ (6. 4 x 106 + 1)2 m 2 = 29. 4 kg m/s 2 Physics 101: Lecture 1, Pg 13

Gravitational ACT l If the book is raised 10 meters above the surface of the earth, the gravitational force on the book will A) 100 times stronger B) 10 times stronger C) Nearly the same D) 10 times weaker E) 100 times weaker F = G M m / r 2 = (6. 7 x 10 -11 m 3 / (kg s 2)) (6 x 1024 kg) (3 kg)/ (6. 4 x 106 + 10)2 m 2 = 29. 4 kg m/s 2 Near surface of earth r = 6. 4 x 106 m |F| = m (G M /r 2) = m (9. 8 m/s 2) Physics 101: Lecture 1, Pg 14

Contact Forces: Friction l Magnitude of frictional force (parallel to surfaces) is proportional to the normal force. èfkinetic = mk N mk coefficient of Kinetic friction èfstatic <= ms N ms coefficient of Static friction l Be Careful! èStatic friction <=, can be any value up to ms. N èDirection always opposes motion Physics 101: Lecture 1, Pg 15

Free Body Diagrams l Choose Object (book) l Label coordinate axis l Identify All Forces èHand (to right) èGravity (down) èNormal (table, up) èFriction (table, left) Physics y x Physics 101: Lecture 1, Pg 16

Summary l Newton’s Laws of Motion èInertia èF=ma èPairs l Forces: èNon-Contact: Gravity èContact: Friction and Normal l Free Body Diagrams èEach direction is independent l Friction opposes motion, parallel to surface èKinetic f = mk N èStatic f <= ms N Physics 101: Lecture 1, Pg 17

To Do l Discussions started already, Labs start today. l Do lecture preflight before 6: 00 am Monday! l Have a GREAT WEEKEND! 50 Physics 101: Lecture 1, Pg 18