1. Energy Introduction Section 0 Lecture 1 Slide 1 Lecture 13 Slide 1 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 13 Energy

2. Introduction Section 0 Lecture 1 Slide 2 Lecture 13 Slide 2 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 PHYSICS OF TECHNOLOGY Spring 2009 Assignment Sheet *Homework Handout

3. Energy Introduction Section 0 Lecture 1 Slide 3 Lecture 13 Slide 3 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 13 Energy Introduction

4. Energy Introduction Section 0 Lecture 1 Slide 4 Lecture 13 Slide 4 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Dennison’s Law of minimum effort: MAKE IT SIMPLE STUPID!!! Einstein on the Theory of General Relativity: “Everything should be made as simple as possible, but not simpler.... “

5. Energy Introduction Section 0 Lecture 1 Slide 5 Lecture 13 Slide 5 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009... Is there some sort of conservation law that is related to Newton’s Laws of motion… Can we build on what we’ve learned to make our life easier…

6. Energy Introduction Section 0 Lecture 1 Slide 6 Lecture 13 Slide 6 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Describing Motion and Interactions Position—where you are in space (L or meter) Velocity—how fast position is changing with time (LT -1 or m/s) Acceleration—how fast velocity is changing with time (LT -2 or m/s 2 ) Force— what is required to change to motion of a body (MLT -2 or kg-m/s 2 ) In this chapter we will develop on of the most useful concepts in science…ENERGY…and learn what it means to conserve energy.

7. Energy Introduction Section 0 Lecture 1 Slide 7 Lecture 13 Slide 7 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Newton’s Laws in Review 1 st Law —a special case of the 2 nd Law for statics, with a=0 or F net =0 An objects velocity remains unchanged, unless a force acts on the object. 2 nd Law (and 1 st 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. 3 rd Law —Forces come from interactions with other objects. For every action (force), there is an equal but opposite reaction (force).

8. Energy Introduction Section 0 Lecture 1 Slide 8 Lecture 13 Slide 8 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What can apply to all these sorts of problems… Forces are acting in each case, but force is not conserved really. F ||

9. Energy Introduction Section 0 Lecture 1 Slide 9 Lecture 13 Slide 9 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 13 Energy Work and Energy

10. Energy Introduction Section 0 Lecture 1 Slide 10 Lecture 13 Slide 10 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Work is equal to the force applied times the distance moved. –Work = Force x Distance: W = F d –Work output = Work input units: 1 joule (J) = 1 Nm = 1 kg m 2 / s 2 [ML 2 T -2 ] Defining Work

11. Energy Introduction Section 0 Lecture 1 Slide 11 Lecture 13 Slide 11 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Only forces parallel to the motion do work. Power is the rate of doing work –Power = Work divided by Time: P = W / t units: 1 watt (W) = 1 J / s = 1 kg m 2 / s 3 [ML 2 T -3 ] Work and Power

12. Energy Introduction Section 0 Lecture 1 Slide 12 Lecture 13 Slide 12 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A string is used to pull a wooden block across the floor without accelerating the block. The string makes an angle to the horizontal. Does the force applied via the string do work on the block? a)Yes, the force F does work. b)No, the force F does no work. c)Only part of the force F does work. d)You can’t tell from this diagram. Only the part of the force that is parallel to the distance moved does work on the block. This is the horizontal part of the force F.

13. Energy Introduction Section 0 Lecture 1 Slide 13 Lecture 13 Slide 13 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 If there is a frictional force opposing the motion of the block, does this frictional force do work on the block? a)Yes, the frictional force does work. b)No, the frictional force does no work. c)Only part of the frictional force does work. d)You can’t tell from this diagram. Since the frictional force is antiparallel to the distance moved, it does negative work on the block.

14. Energy Introduction Section 0 Lecture 1 Slide 14 Lecture 13 Slide 14 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Does the normal force of the floor pushing upward on the block do any work? a)Yes, the normal force does work. b)No, the normal force does no work. c)Only part of the normal force does work. d)You can’t tell from this diagram. Since the normal force is perpendicular to the distance moved, it does no work on the block.

15. Energy Introduction Section 0 Lecture 1 Slide 15 Lecture 13 Slide 15 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 A force of 50 N is used to drag a crate 4 m across a floor. The force is directed at an angle upward from the crate as shown. What is the work done by the horizontal component of the force? a)120 J b)160 J c)200 J d)280 J e)0 J The horizontal component of force is 40 N and is in the direction of motion: W = F · d = (40 N) · (4 m) = 160 J.

16. Energy Introduction Section 0 Lecture 1 Slide 16 Lecture 13 Slide 16 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What is the work done by the vertical component of the force? a)120 J b)160 J c)200 J d)280 J e)0 J The vertical component of force is 30 N but isn’t in the direction of motion: W = F · d = (30 N) · (0 m) = 0 J.

17. Energy Introduction Section 0 Lecture 1 Slide 17 Lecture 13 Slide 17 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 What is the total work done by the 50-N force? a)120 J b)160 J c)200 J d)280 J e)0 J Only the component of force in the direction of motion does work: W = F · d = (40 N) · (4 m) = 160 J.

18. Energy Introduction Section 0 Lecture 1 Slide 18 Lecture 13 Slide 18 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology PHYS 1800 Lecture 13 Energy Energy and Simple Machines

19. Energy Introduction Section 0 Lecture 1 Slide 19 Lecture 13 Slide 19 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Simple Machines, Work, and Power A simple machine multiplies the effect of an applied force. –For example, a lever : A small force applied to one end delivers a large force to the rock. The small force acting through a large distance moves the rock a small distance. F 2 d 2 = F 1 d 1

20. Energy Introduction Section 0 Lecture 1 Slide 20 Lecture 13 Slide 20 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Simple Machines, Work, and Power A simple machine multiplies the effect of an applied force. –For example, a pulley : A small tension applied to one end delivers twice as much tension to lift the box. The small tension acting through a large distance moves the box a small distance.

21. Energy Introduction Section 0 Lecture 1 Slide 21 Lecture 13 Slide 21 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 The mechanical advantage of a simple machine is the ratio of the output force to the input force. –For the pulley example, the mechanical advantage is 2. Work is equal to the force applied times the distance moved. –Work = Force x Distance: W = F d –Work output = Work input units: 1 joule (J) = 1 Nm= 1 kg m 2 / s 2 [ML 2 T -2 ] Mechanical Advantage and Simple Machines

22. Energy Introduction Section 0 Lecture 1 Slide 22 Lecture 13 Slide 22 INTRODUCTION TO Modern Physics PHYX 2710 Fall 2004 Physics of Technology—PHYS 1800 Spring 2009 Physics of Technology Next Lab/Demo: Energy & Oscillations Collisions and Momentum Thursday 1:30-2:45 ESLC 53 Ch 6 Next Class: Friday 10:30-11:20 BUS 318 room Review Ch 6