Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 7 Part 1 + Brief Review.

Slides:



Advertisements
Similar presentations
Physics 207: Lecture 13, Pg 1 Lecture 13 Goals: Assignment: l HW6 due Wednesday, Feb. 11 l For Thursday: Read all of Chapter 11 Chapter 10 Chapter 10 
Advertisements

Which of the following is the best description of the dot product ? Dot Product.
ConcepTest 6.5a Kinetic Energy I
ConcepTest Clicker Questions
Conservation of Energy
Gravitational potential energy. Conservation of energy
An object is released from rest on a planet that
Sect. 8-3: Mechanical Energy & It’s Conservation.
Physics 203 College Physics I Fall 2012
Work, Energy, And Power m Honors Physics Lecture Notes.
Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 6 Part 1 Work and Kinetic.
Work and Energy Chapter 7.
Chapter 9:Linear Momentum 8-4 Problem Solving Using Conservation of Mechanical Energy 8-5 The Law of Conservation of Energy 8-6 Energy conservation with.
The first exam will be held on Tuesday, September 23, in room 109 Heldenfels from 7 to 9:30 p.m. Section 807 and half of section 808 (students with last.
Physics 151: Lecture 15, Pg 1 Today’s Topics l Potential Energy, Ch. 8-1 l Conservative Forces, Ch. 8-2 l Conservation of mechanical energy Ch.8-4.
Physics 218: Mechanics Instructor: Dr. Tatiana Erukhimova Lectures
Conservation of Energy
Dec. 8, 2001 Prof. Todd Adams, FSU Department of Physics1 Physics 2053C – Fall 2001 Review for Final Exam
Physics 2.2.
WORK In order for work to be done, three things are necessary:
WORK AND ENERGY 1. Work Work as you know it means to do something that takes physical or mental effort But in physics is has a very different meaning.
by the normal force acting on a sliding block?
Chapter 6 Energy and Energy Transfer. Introduction to Energy The concept of energy is one of the most important topics in science Every physical process.
Chapter 5 Work and Energy. Review  x = v i  t + ½ a  t 2  x = ½ (v i + v f )  t v f = v i + a  t v f 2 = v i 2 + 2a  x.
Copyright © 2010 Pearson Education, Inc. Chapter 7 Work and Kinetic Energy.
Physics 201: Lecture 13, Pg 1 Lecture 13 l Goals  Introduce concepts of Kinetic and Potential energy  Develop Energy diagrams  Relate Potential energy.
Potential Energy and Conservative Forces
Preview Objectives Definition of Work Chapter 5 Section 1 Work.
Energy m m Physics 2053 Lecture Notes Energy.
Chapter 7 Energy of a System. The concept of energy is one of the most important topics in science and engineering Every physical process that occurs.
Physics 203 College Physics I Fall 2012
1 Physics 1100 – Spring 2009 Review for Exam I Friday, February 27 th Chapters
Forces and the Laws of Motion
Work and Energy. Work, Power, & Energy Energy offers an alternative analysis of motion and its causes. Energy is transformed from 1 type to another in.
Work and Energy Chapter 7 Conservation of Energy Energy is a quantity that can be converted from one form to another but cannot be created or destroyed.
Physics 215 – Fall 2014Lecture Welcome back to Physics 215 Today’s agenda: Work Non-conservative forces Power.
Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 8 Part 3 Chapter 9 Angular.
Potential Energy ~March 1, 2006.
Reading Quiz - Work & Energy
NAZARIN B. NORDIN What you will learn: Define work, power and energy Potential energy Kinetic energy Work-energy principle Conservation.
Work and Energy Work is the product of Force and displacement. The force needed to calculate Work is the force or component force in the direction of.
Physics 215 – Fall 2014Lecture Welcome back to Physics 215 Today’s agenda: More gravitational potential energy Potential energy of a spring Work-kinetic.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives Definition of Work Chapter 5 Section 1 Work.
Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 7 Part 2 Momentum and Collisions.
7.4) Kinetic Energy andThe Work-Kinetic Energy Theorem Figure (7.13) - a particle of mass m moving to the right under the action of a constant net force.
Chapter 7 Energy of a System.
Work has a specific definition in physics
Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 8 Part 1 Rotational Motion.
Work and Energy x Work and Energy 06.
Ch. 6, Work & Energy, Continued. Summary So Far Work-Energy Theorem: W net = (½)m(v 2 ) 2 - (½)m(v 1 ) 2   KE Total work done by ALL forces! Kinetic.
Review - II (chapters 5 and 6) Newton's 1st law: If no force acts on a body, then the body's velocity cannot change; that is, it cannot accelerate. Mass.
Final Exam Review (Day 1).  Energy Lecture Review  Kinetic & Potential Energy  Net Work (W net = F net  x = F net cos  )  Work-Kinetic Energy Theorem.
Monday, October 5, 1998 Chapter 5: Springs Chapter 6: Linear Momentum Conservation of Momentum Impulse.
Work and Energy. Work… …is the product of the magnitude of displacement times the component of force parallel to the displacement. W = F ‖ d Units: N.
© Houghton Mifflin Harcourt Publishing Company Preview Objectives Definition of Work Chapter 5 Section 1 Work.
Thursday, Oct. 30, 2014PHYS , Fall 2014 Dr. Jaehoon Yu 1 PHYS 1443 – Section 004 Lecture #19 Thursday, Oct. 30, 2014 Dr. Jaehoon Yu Rolling Kinetic.
WORK & ENERGY Physics, Chapter 5. Energy & Work What is a definition of energy? Because of the association of energy with work, we begin with a discussion.
Wednesday June 15, PHYS , Summer I 2005 Dr. Andrew Brandt PHYS 1443 – Section 001 Lecture #9 Wednesday June 15, 2005 Dr. Andrew Brandt Lightning.
Chapter 8 Conservation of Energy EXAMPLES. Example 8.1 Free Fall (Example 8.1 Text book) Determine the speed of the ball at y above the ground The sum.
Chapter 8 Momentum Definition of Total Momentum The total momentum P of any number particles is equal to the vector sum of the momenta of the individual.
Physics 207: Lecture 15, Pg 1 Lecture 15 Goals: Chapter 11 (Work) Chapter 11 (Work)  Employ conservative and non-conservative forces  Relate force to.
Monday, Oct. 14, 2002PHYS , Fall 2002 Dr. Jaehoon Yu 1 PHYS 1443 – Section 003 Lecture #9 Monday, Oct. 14, 2002 Dr. Jaehoon Yu 1.Conservation of.
Copyright © by Holt, Rinehart and Winston. All rights reserved. ResourcesChapter menu Section 1 Work Chapter 5 Definition of Work Work is done on an object.
Chapter 6 Work and Energy © 2014 Pearson Education, Inc. No need to write information in red.
Conservation of Energy Or the More things change the more they stay the same.
Wednesday, Oct. 17, 2007 PHYS , Fall 2007 Dr. Jaehoon Yu 1 PHYS 1443 – Section 002 Lecture #13 Wednesday, Oct. 17, 2007 Dr. Jaehoon Yu Potential.
Chapter 5 Work and Energy
Gravitational Potential Energy and Reference level
PHYS 1443 – Section 003 Lecture #9
Presentation transcript:

Physics 203 – College Physics I Department of Physics – The Citadel Physics 203 College Physics I Fall 2012 S. A. Yost Chapter 7 Part 1 + Brief Review for Exam Momentum and Impulse

Physics 203 – College Physics I Department of Physics – The Citadel Announcements The Exam on Chapters 4 – 6 will be Thursday. Next Tuesday: Read Ch. 7, but you can skip sections 7.7 and 7.9. A problem set HW07A is already open and due next Tuesday. It covers sections 1 – 3, 8, and 9 in Chapter 7. A problem set HW07B on sections 4 – 6 (collisions) will be posted soon and due next Thursday.

Physics 203 – College Physics I Department of Physics – The Citadel Energy Conservation When only conservative forces act on a system, energy is conserved. All of the fundamental forces in the universe are conservative. That means that if you keep track of the total energy in a closed system, it can never increase or decrease – it can only change form.

Physics 203 – College Physics I Department of Physics – The Citadel Energy Conservation The total energy is the sum of the kinetic energy and the potential energy of an object. The potential energy is the amount of work it took to put the object in its current position. It is normally written as U. For example, the potential energy of a book of mass m on top of a cabinet of height h is U = mgh. The potential energy of a spring compressed or stretched a distance x from equilibrium is U = ½ kx 2.

Physics 203 – College Physics I Department of Physics – The Citadel Water Slide Two water slides have the same length, but are shaped different. Who is going faster at the bottom of the slides? A) Paul B) Kathleen C) No difference

Physics 203 – College Physics I Department of Physics – The Citadel Water Slide Who gets to the bottom first? A) Paul B) Kathleen C) No difference

Physics 203 – College Physics I Department of Physics – The Citadel Power Power is the rate of doing work: P = W/t. If the force F acts in the direction of motion, then P = Fv (instantaneous) These are consistent because x = v t is the distance traveled, so P = F v = F x/t = W/t. Horsepower: 1 hp = 746 W.

Physics 203 – College Physics I Department of Physics – The Citadel The Exam Topics on Exam: Chapter 4: Newton’s Laws Free body diagrams, F = ma, … Chapter 5: Circular motion, Universal gravitation. a c = v 2 /R, F = ma, F g = Gm 1 m 2 /R, orbits Chapter 6: kinetic energy, work, W =  K, potential energy, power →

Physics 203 – College Physics I Department of Physics – The Citadel The Effect of a Force over Time We say that when a force F acts for time t, a mass acquires momentum m v = m a t = F t. If the force is changing, we can use the time- averaged force: m v = F avg t. The right-hand side of the equation is called the impulse. → → → → →

Physics 203 – College Physics I Department of Physics – The Citadel Impulse and Momentum The momentum can be written as p = mv. The impulse can be written J = F avg t. Newton’s second law implies that the net impulse equals the change in momentum.  p = J →

Physics 203 – College Physics I Department of Physics – The Citadel Impulsive Forces Momentum can be used in any dynamical situation, but is especially useful for impulsive forces, which act over a short time. The impulse is the area under the curve, geometrically.

Physics 203 – College Physics I Department of Physics – The Citadel Impulse and Average Force The impulse is also equal to the average force times the time interval: (same area in blue) J(t) = F avg  t →

Physics 203 – College Physics I Department of Physics – The Citadel Conservation of Momentum If there is no external force on a system of objects, then its total momentum cannot change, since there is no net impulse. The total momentum of a system isolated from external forces is conserved.

Physics 203 – College Physics I Department of Physics – The Citadel Center of Mass The center of mass a set of objects is the average position of their mass. For two objects in 1D: x 1 m 1 + x 2 m 2 m 1 + m 2 m1m1 m2m2 x1x1 x2x2 CM x cm = x cm

Physics 203 – College Physics I Department of Physics – The Citadel Center of Mass In more dimensions you can use vectors to locate the CM: m 1 r 1 + m 2 r 2 + m 3 r 3 m 1 + m 2 + m 3 It moves with velocity m1m1 m2m2 r1r1 r3r3 CM m2m2 r2r2 r cm = m 1 v 1 + m 2 v 2 + m 3 v 3 m 1 + m 2 + m 3 v cm = P = M v cm

Physics 203 – College Physics I Department of Physics – The Citadel Motion of the Center of Mass If an external force F acts on an extended object or collection of objects of mass M, the acceleration of the CM is given by F = Ma cm. You can apply Newton’s 2 nd Law as if it were a particle located at the CM, as far as the collective motion is concerned. This says nothing about the relative motion, rotation, etc., about the CM. That comes up in chapter 8.

Physics 203 – College Physics I Department of Physics – The Citadel Motion of Extended Objects The motion of extended objects or collections of particles is such that the CM obeys Newton’s 2 nd Law.

Physics 203 – College Physics I Department of Physics – The Citadel Motion of the Center of Mass The CM of a wrench sliding on a frictionless table will move in a straight line because there is no external force. In this sense, the wrench may be though of as a particle located at the CM. cm motion

Physics 203 – College Physics I Department of Physics – The Citadel Motion of the Center of Mass For example, if a hammer is thrown, its CM follows a parabolic trajectory under the influence of gravity, as a point object would.

Physics 203 – College Physics I Department of Physics – The Citadel Motion of the Center of Mass For example, if a hammer is thrown, its CM follows a parabolic trajectory under the influence of gravity, as a point object would.

Physics 203 – College Physics I Department of Physics – The Citadel Additional Slides Problems for extra practice on chapter 6 follow.

Physics 203 – College Physics I Department of Physics – The Citadel Compressed Spring When a box is set gently on a spring, it compresses it a distance d. What would happen if I hold it at the uncompressed position, and then let go?

Physics 203 – College Physics I Department of Physics – The Citadel Compressed Spring The spring will compress – how far?  U = – mgh – ½ kh 2 = 0 h = 2mg/k = 2d.

Physics 203 – College Physics I Department of Physics – The Citadel Compressed Spring Then what happens? Where does the box attain its maximum speed? v is maximum where U is a minimum. This is the equilibrium position.

Physics 203 – College Physics I Department of Physics – The Citadel Compressed Spring What is the maximum speed? Start at the top:  K +  U = 0 ½ mv 2 – mgd + ½ kd 2 = 0 v 2 = 2gd – (k/m)d 2 with k = mg/d. v 2 = 2gd – gd = gd. v = √gd

Physics 203 – College Physics I Department of Physics – The Citadel Example How long will it take 50 hp motor to pull a 120 kg sled 100 m up a hill, if the coefficient of kinetic friction is , and the elevation increases by 20 m on the way up? Assume a constant slope and speed.

Physics 203 – College Physics I Department of Physics – The Citadel Example First find the work done by the motor. Assume the net work is zero. W m + W f =  U = mgh = 2.35 ×10 4 J. h = 20 m

Physics 203 – College Physics I Department of Physics – The Citadel Example Work done by friction? W f = –F f d F f =  N, N = mg cos   F f  mg cos  h = 20 m d = 100 m θ θ N → FfFfFfFf → → mgmg = –  mg (cos  ) d = –  mg x =√ – 20 2 m x  = 0.10 m = 120 kg x = 98 m = – 1.15 ×10 4 J

Physics 203 – College Physics I Department of Physics – The Citadel Example W m = mgh – W f = 2.35 ×10 4 J – (– 1.15 ×10 4 J ) = 3.50 ×10 4 J. Time: t = W m /P m P m = 5.0 hp (746 W/hp) = 3730 W. t = 9.4 s. h = 20 m