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Newton's Laws and Equilibrium: Solving Linear Force and Motion Problems

This chapter covers Newton's laws of motion, equilibrium problems, and solving linear force and motion problems. Topics include static, inertial, and dynamic equilibrium, mass, gravity, weight, friction, and terminal speed.

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Newton's Laws and Equilibrium: Solving Linear Force and Motion Problems

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  1. Chapter 6 Lecture

  2. Chapter 6 Dynamics I: Motion Along a Line Chapter Goal: To learn how to solve linear force-and-motion problems. Slide 6-2

  3. Chapter 6 Preview Slide 6-3

  4. Chapter 6 Preview Slide 6-4

  5. Chapter 6 Preview Slide 6-5

  6. Chapter 6 Preview Slide 6-6

  7. Chapter 6 Preview Slide 6-7

  8. Chapter 6 Preview Slide 6-8

  9. Chapter 6 Reading Quiz Slide 6-9

  10. Reading Question 6.1 Newton’s first law can be applied to • Static equilibrium. • Inertial equilibrium. • Dynamic equilibrium. • Both A and B. • Both A and C. Slide 6-10

  11. Reading Question 6.1 Newton’s first law can be applied to • Static equilibrium. • Inertial equilibrium. • Dynamic equilibrium. • Both A and B. • Both A and C. Slide 6-11

  12. Reading Question 6.2 Mass is • An intrinsic property. • A force. • A measurement. Slide 6-12

  13. Reading Question 6.2 Mass is • An intrinsic property. • A force. • A measurement. Slide 6-13

  14. Reading Question 6.3 Gravity is • An intrinsic property. • A force. • A measurement. Slide 6-14

  15. Reading Question 6.3 Gravity is • An intrinsic property. • A force. • A measurement. Slide 6-15

  16. Reading Question 6.4 Weight is • An intrinsic property. • A force. • A measurement. Slide 6-16

  17. Reading Question 6.4 Weight is • An intrinsic property. • A force. • A measurement. Slide 6-17

  18. Reading Question 6.5 The coefficient of static friction is • Smaller than the coefficient of kinetic friction. • Equal to the coefficient of kinetic friction. • Larger than the coefficient of kinetic friction. • Not discussed in this chapter. Slide 6-18

  19. Reading Question 6.5 The coefficient of static friction is • Smaller than the coefficient of kinetic friction. • Equal to the coefficient of kinetic friction. • Larger than the coefficient of kinetic friction. • Not discussed in this chapter. Slide 6-18

  20. Reading Question 6.6 The force of friction is described by • The law of friction. • The theory of friction. • A model of friction. • The friction hypothesis. Slide 6-20

  21. Reading Question 6.6 The force of friction is described by • The law of friction. • The theory of friction. • A model of friction. • The friction hypothesis. Slide 6-21

  22. Reading Question 6.7 When an object moves through the air, the magnitude of the drag force on it • Increases as the object’s speed increases. • Decreases as the object’s speed increases. • Does not depend on the object’s speed. Slide 6-22

  23. Reading Question 6.7 When an object moves through the air, the magnitude of the drag force on it • Increases as the object’s speed increases. • Decreases as the object’s speed increases. • Does not depend on the object’s speed. Slide 6-23

  24. Reading Question 6.8 Terminal speed is • Equal to the speed of sound. • The minimum speed an object needs to escape the earth’s gravity. • The speed at which the drag force cancels the gravitational force. • The speed at which the drag force reaches a minimum. • Any speed which can result in a person’s death. Slide 6-24

  25. Reading Question 6.8 Terminal speed is • Equal to the speed of sound. • The minimum speed an object needs to escape the earth’s gravity. • The speed at which the drag force cancels the gravitational force. • The speed at which the drag force reaches a minimum. • Any speed which can result in a person’s death. Slide 6-25

  26. Chapter 6 Content, Examples, and QuickCheck Questions Slide 6-26

  27. Equilibrium • An object on which the net force is zero is in equilibrium. • If the object is at rest, it is in static equilibrium. • If the object is moving along a straight line with a constant velocity it is in dynamic equilibrium. • The requirement for either type of equilibrium is: The concept of equilibrium is essential for the engineering analysis of stationary objects such as bridges. Slide 6-27

  28. QuickCheck 6.1 The figure shows the view looking down onto a sheet of frictionless ice. A puck, tied with a string to point P, slides on the ice in the circular path shown and has made many revolutions. If the string suddenly breaks with the puck in the position shown, which path best represents the puck’s subsequent motion? Slide 6-28

  29. QuickCheck 6.1 The figure shows the view looking down onto a sheet of frictionless ice. A puck, tied with a string to point P, slides on the ice in the circular path shown and has made many revolutions. If the string suddenly breaks with the puck in the position shown, which path best represents the puck’s subsequent motion? Newton’s first law! Slide 6-29

  30. Problem-Solving Strategy: Equilibrium Problems Slide 6-30

  31. Problem-Solving Strategy: Equilibrium Problems Slide 6-31

  32. QuickCheck 6.2 A ring, seen from above, is pulled on by three forces. The ring is not moving. How big is the force F? • 20 N • 10cos N • 10sin N • 20cos N • 20sin N Slide 6-32

  33. QuickCheck 6.2 A ring, seen from above, is pulled on by three forces. The ring is not moving. How big is the force F? • 20 N • 10cos N • 10sin N • 20cos N • 20sin N Slide 6-33

  34. Example 6.2 Towing a Car up a Hill Slide 6-34

  35. Example 6.2 Towing a Car up a Hill Slide 6-35

  36. Example 6.2 Towing a Car up a Hill Slide 6-36

  37. Example 6.2 Towing a Car up a Hill Slide 6-37

  38. Example 6.2 Towing a Car up a Hill Slide 6-38

  39. QuickCheck 6.3 A car is parked on a hill. Which is the correct free-body diagram? Slide 6-39

  40. QuickCheck 6.3 A car is parked on a hill. Which is the correct free-body diagram? Slide 6-40

  41. QuickCheck 6.4 A car is towed to the right at constant speed. Which is the correct free-body diagram? Slide 6-41

  42. QuickCheck 6.4 A car is towed to the right at constant speed. Which is the correct free-body diagram? Slide 6-42

  43. Using Newton’s Second Law The essence of Newtonian mechanics can be expressed in two steps: • The forces on an object determine its   acceleration , and • The object’s trajectory can be determined by   using in the equations of kinematics. Slide 6-43

  44. Problem-Solving Strategy: Dynamics Problems Slide 6-44

  45. Problem-Solving Strategy: Dynamics Problems Slide 6-45

  46. 1 1 2 4 QuickCheck 6.5 The cart is initially at rest. Force is applied to the cart for time t, after which the car has speed v. Suppose the same force is applied for the same time to a second cart with twice the mass. Friction is negligible. Afterward, the second cart’s speed will be • v • v • v • 2v • 4v Slide 6-46

  47. 1 1 2 4 QuickCheck 6.5 The cart is initially at rest. Force is applied to the cart for time t, after which the car has speed v. Suppose the same force is applied for the same time to a second cart with twice the mass. Friction is negligible. Afterward, the second cart’s speed will be • v • v • v • 2v • 4v Slide 6-47

  48. Example 6.3 Speed of a Towed Car Slide 6-48

  49. Example 6.3 Speed of a Towed Car Slide 6-49

  50. Example 6.3 Speed of a Towed Car Slide 6-50

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