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Transcript
Physics of Technology PHYS 1800 Lecture 10 Introduction Review for Test 1 Section 0 Lecture 1 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 1 PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet Date Day Lecture Chapter Jan 5 M Class Admin: Intro.Physics Phenomena 1 6 T Problem solving and math App. B, C 7 W Units, Scalars, Vectors, 1 9 F* Speed and Velocity 2 Jan 12 M Acceleration 2 14 W Free Falling Objects 3 16 F* Projectile Motion 3 Jan 19 M Martin Luther King No Class 21 W Newton’s Laws 4 23 F* Mass and Weight 4 Jan 26 M Motion with Friction 4 28 W Review 1-4 1-4 29 Th Test 1 30 F Circular Motion 5 Feb 2 M Planetary Motion and Gravity 5 4 W Energy 6 6 F* Harmonic Motion 6 Feb 9 M Momentum 7 11 W Impulse and Collisions 7 13Introduction F* Rotational 8 Section 0 Motion Lecture 1 Slide 2 Feb 16 M Presidents Day No Class 17 Tu Angular Momentum (Virtual Monday) 8 18 W Review 5-8 19 5-8 H Test 2 INTRODUCTION TO Modern Physics PHYX 2710 20 F* Static Fluids, Pressure 9 Fall 2004 Feb 23 M Flotation 9 25 W Fluids in Motion 9 27 F* Temperature and Heat 10 Mar 2 M First Law of Thermodynamics 10 Physics of Technology—PHYS 1800 4 W Spring 2009Heat flow and Greenhouse Effect Review 10 *Homework Handout 6 F* Climate Change - Homework Due - 1 2 3 4 5 - 6 Lecture 10 Slide 2 7 Physics of Technology PHYS 1800 Lecture 8 Mass & Weight Motion with Friction Introduction Section 0 Lecture 1 Slide 3 Introduction and Review INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 3 Notes on Test 1. Covers Chapters 1-4 2. ~8 short answer problems or questions (5 point each) 3. 3 Numerical problems based heavily on the material from the homework and Lab/Demo sessions (20 points each). One problem each from Chapters 2, 3 and 4. 4. You will have a formula sheet just like the one in Introduction Section 0 Lecture 1 Slide 4 the handout. 5. Test is Thursday January 29 1:30-2:45 in ESLC 46. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 4 What Do We Need To Measure? • What is the minimum about things we need to know? • Where things are—a length, L • When things are there—a time, T • How thing interact with gravity—a mass, M • How things interact with E&M—a charge, Q Introduction Section 0 Lecture 1 Slide 5 • How thing inter act with weak nuclear force • How things interact with strong nuclear force INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 5 Scalars and Vectors • Scalar: Measure of quantity or size • Sometimes called “magnitude”. • Examples: Length, volume, mass, temperature, speed… • Vectors: Many measurements in physics require a knowledge of the magnitude and direction of quantity. • These are termed vector quantities. • Examples: Velocity, acceleration, force, electric field… • Direction is an essential feature of a vector quantity. Introduction Section 0 Lecture 1 Slide 6 • Example: Flying at 1000 km/hr due North is quite different to the same speed due East! INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 • Vectors require 2 pieces of information MAGNITUDE and DIRECTION. Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 6 Describing (Special) Motion Position—where you are in space (L-meter) Speed—how fast position is changing with time (LT-1 or m/s) Acceleration—how fast speed is changing with time (LT-2 or m/s2) 1 Slide 7 We willIntroduction focusSection on0 aLecture special case of constant acceleration due to gravity, termed FREE FALL. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 7 Acceleration Speed Distance Constant Acceleration Time Time Introduction Section 0 Lecture 1 Time Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 8 The Math Approach • Let’s put these ideas into math language ag v f v0 at or a v f vo t v f vo v f vo vo vo t t t d vavg t 2 2 2 2 v1f Slidev9o vo 0 Lecture 1 2 vo Section Introduction d t t v0t at 2 2 2 2 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 9 • Let the initial velocity be 20 m/s upward. – It immediately starts experiencing a downward acceleration due to gravity, of approximately 10 m/s. – Every second, the velocity decreases by 10 m/s. • After 2 s, the ball has reached its highest point. – Its velocity changes direction, from upward to downward, passing through a value of 0 m/s. Introduction Section 0 Lecture 1 Slide 10 • Now, the downward acceleration increases the downward velocity. INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 10 Which of these three balls would hit the floor first if all three left the tabletop at the same time? a) b) c) d) The ball with initial velocity v1. The ball with initial velocity v2. The ball with initial velocity v3. They would all hit at the same time. Since all three balls undergo the same downward acceleration, and Introduction Section 0 Lecture 1 they all start with a vertical velocity of zero, they would all fall the same distance in the same time! Slide 11 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 11 Projectile Motion • Treating the vertical motion independently of the horizontal motion, and then combining them to find the trajectory, is the secret. – A horizontal glide combines with a vertical plunge to produce a graceful curve. – The downward gravitational acceleration behaves the same as for any falling object. – There is no acceleration in the horizontal direction if air resistance can be ignored. – The projectile moves with constant horizontal velocity while it is accelerating downward. Introduction Section 0 Lecture 1 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 12 Dennison’s Laws of Motion 1. Stuff happens (or not). 2. The bigger they are the harder they fall. 3. You get what you give. Introduction Section 0 Lecture 1 Slide 13 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 13 Newton’s Laws in Review • 1st Law —a special case of the 2nd Law for statics, with a=0 or Fnet=0 • An objects velocity remains unchanged, unless a force acts on the object. • 2nd Law (and 1st Law)—How motion of a object is effected by a force. – The acceleration of an object is directly proportional to the magnitude of the imposed force and inversely proportional to the mass of the object. The acceleration is the same direction as that of the imposed force. F ma units : 1 newton = 1 N = 1 kg m s2 • Introduction Section 0 Lecture 1 3rd Law —Forces come Slide 14 from interactions with other objects. • For every action (force), there is an equal but opposite reaction (force). INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 14 Newton’s First Law of Motion An object remains at rest, or in uniform motion in a straight line, unless it is compelled to change by an externally imposedIntroduction force. Section 0 Lecture 1 Slide 15 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 15 Newton’s Second Law of Motion Note that a force is proportional to an object’s acceleration, not its velocity. Precise definitions of some commonly used terms: The mass of an object is a quantity that tells us how much resistance the object has to a change in its motion. This resistance to a change in motion is called inertia. F ma Introduction Section 0 Lecture 1 Slide 16 units : 1 newton = 1 N = 1 kg m s2 Force has dimensions of (MLT-2) INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 16 Fstring 10 N (to the right) Net Forces It is the total force or net force that determines an object’s acceleration. If there is more than one vector acting on an object, the forces are added together as vectors, taking into account their directions. ftable 2 N (to the left) Fnet 10 N 2 N 8 N (to the right) Fnet 8 N a m 5 kg 1.6 m s2 (to the right) Introduction Section 0 Lecture 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Slide 17 Review Lecture 10 Slide 17 Newton’s Third Law (“action/reaction”) For every action (force), there is an equal but opposite reaction (force). Introduction Section 0 Lecture 1 Slide 18 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 18 Mass, Weight, and Inertia • A much larger force is required to produce the same acceleration for the larger mass. • Inertia is an object’s resistance to a change in its motion. • Mass is a measure of an object’s inertia. Introduction Section 0 Lecture 1 Slide 19 • The units of mass are kilograms (kg). INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 19 Does a sky diver continue to accelerate? Air resistance R is a force directed upward, that opposes the gravitational force W R increases as the sky diver’s velocity increases When R has increased to the magnitude of W, the net force is zero so the acceleration is zero Introduction Section 0 Lecture 1 Slide 20 The velocity is then at its maximum value, the terminal velocity INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 20 Free Body Diagrams • Fancy Science: Vector analysis of complex force problems is facilitated by use of a free body diagram. • Common Sense: A picture is worth a 100 words. (A scale picture is worth an A!) • Key is to: • Isolate a single body and draw all the forces acting on it. • Add up all the arrows (vectors). Introduction Section 0 Lecture 1 Slide 21 • What’s left is the net force. • Net force (and masses) a. • A plus initial conditions motion! INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 21 Example: Sea Lion splash! Fk N Fk N F|| =mg sinθ θ mg cosθ F|| θ Free body diagram θ W=mg W=mg Resolve the weight force into two components – parallel and perpendicular to ramp. Result: - Down slope force F|| = m g sin θ - Normal force N = m g cos θ Introduction Section 0 Lecture 1 Slide 22 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Review Lecture 10 Slide 22