1. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Motion and Newton’s first law What is a force? Identifying forces Newton’s second law Free-body diagrams Newton’s third law Chapter 4 Forces and Newton’s Laws of Motion Topics: Sample question: These ice boats sail across the ice at great speeds. What gets the boats moving in the first place? What keeps them from going even faster? Slide 4-1

2. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 1.What is a “net force?” Slide 4-2

3. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 2. List at least three of the steps used to identify the forces acting on an object. A. Identify “the system” and “the environment.” B. Draw a picture of the situation. C. Draw a closed curve around the system. D. Locate every point on the boundary of this curve where the environment touches the system. E. Name and label each contact force acting on the object. F. Name and label each long-range force acting on the object. Slide 4-3

4. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 3.Which of these is not a force discussed in this chapter? A.The tension force.C.The orthogonal force. B.The normal force.D.The thrust force. Slide 4-4

5. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 3.Which of these is not a force discussed in this chapter? C.The orthogonal force. Slide 4-5 Answer

6. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Reading Quiz 4.An action/reaction pair of forces A.point in the same direction. B.act on the same object. C.are always long-range forces. D.act on two different objects. Slide 4-6

7. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 4.An action/reaction pair of forces D.act on two different objects. Slide 4-7 Answer

8. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. What Causes Motion? In the absence of any forces acting on it, an object will continue moving forever. Motion needs no “cause.” Slide 4-8

9. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 4-9 Seat Belts: An Application of Newton’s First Law

10. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. What Is a Force? A force...... is a push or pull.... acts on an object.... requires an agent.... is a vector.... is a contact force or a long-range force. Slide 4-10

11. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Force Vectors Slide 4-11

12. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. A Short Catalog of Forces: Weight w Slide 4-12  

13. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Spring Force F sp Slide 4-13 

14. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Tension Force Slide 4-14

15. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Normal Force Slide 4-15

16. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Slide 4-16 Friction f k and 

17. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Drag and Thrust Slide 4-17

18. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Identifying Forces Slide 4-18

19. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Example A block is dragged uphill by a rope. Identify all forces acting on the block. Slide 4-19

20. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Example Block A hangs from the ceiling by a rope. Another block B hangs from A. Identify the forces acting on A. Slide 4-20

21. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Exercise A ball, hanging from the ceiling by a string, is pulled back and released. Identify the forces acting on it just after its release. Slide 4-21

22. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton’s Second Law Slide 4-22

23. Example An elevator, lifted by a cable, is going up at a steady speed. Identify the forces acting on the elevator. Is T greater than, equal to, or less than w? Or is there not enough information to tell? Slide 4-23

24. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Free-Body Diagrams Slide 4-24

25. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Newton’s Third Law Slide 4-25

26. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Identifying Forces for Interacting Objects Slide 4-26

27. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. Checking Understanding 10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is A.greater than the force of Sarah on Jack. B.equal to than the force of Sarah on Jack. C.less than the force of Sarah on Jack. Slide 4-27

28. Copyright © 2007, Pearson Education, Inc., Publishing as Pearson Addison-Wesley. 10-year-old Sarah stands on a skateboard. Her older brother Jack starts pushing her backward and she starts speeding up. The force of Jack on Sarah is B.equal to than the force of Sarah on Jack. Slide 4-28 Answer