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1. Chapter Introduction Lesson 1 Gravity and Friction Lesson 2 Newton’s First Law Lesson 3Newton’s Second Law Lesson 4 Newton’s Third Law Chapter Wrap-Up Chapter Menu

2. How do forces change the motion of objects? Chapter Introduction

3. What do you think? Before you begin, decide if you agree or disagree with each of these statements. As you view this presentation, see if you change your mind about any of the statements. Chapter Introduction

4. 1. You pull on objects around you with the force of gravity. 2. Friction can act between two unmoving, touching surfaces. 3. Forces acting on an object cannot be added. Do you agree or disagree? Chapter Introduction

5. 4. A moving object will stop if no forces act on it. 5. When an object’s speed increases, the object accelerates. 6. If an object’s mass increases, its acceleration also increases if the net force acting on the object stays the same. Do you agree or disagree? Chapter Introduction

6. 7. If objects collide, the object with more mass applies more force. 8. Momentum is a measure of how hard it is to stop a moving object. Do you agree or disagree? Chapter Introduction

7. Gravity and Friction • What are some contact forces and some noncontact forces? • What is the law of universal gravitation? • How does friction affect the motion of two objects sliding past each other? Lesson 1 Reading Guide - KC

8. Gravity and Friction • mass • weight • friction • force • contact force • noncontact force • gravity Lesson 1 Reading Guide - Vocab

9. Types of Forces • A push or a pull is called a force. • An object or a person can apply a force to another object or person. force from Latin fortis, means “strong” Lesson 1-1

10. Types of Forces(cont.) • A contact force is a force that is applied when two objects touch. • A force that one object can apply to another object without touching it is a noncontact force. • Gravity and magnetic force are examples of noncontact forces. Lesson 1-1

11. Types of Forces(cont.) What are some contact forces and some noncontact forces? Lesson 1-1

12. What is gravity? • Gravity is an attractive force that exists between all objects that have mass. • Objects fall to the ground because Earth exerts gravity on them. • Mass is the amount of matter in an object. • Mass is often measured in kilograms (kg). Lesson 1-2

13. The SI unit for force is the newton (N). • Arrows can be used to show both the strength and direction of force. Lesson 1-1

14. What is gravity?(cont.) • Sir Isaac Newton developed the law of universal gravitation in the late 1600s. • The law of universal gravitation states that all objects are attracted to each other by a gravitational force. Lesson 1-2

15. What is gravity?(cont.) What is the law of universal gravitation? Lesson 1-2

16. What is gravity?(cont.) • The strength of force depends on the mass of each object and the distance between them. • When the mass of one or both objects increases, the gravitational force between them also increases. Lesson 1-2

17. What is gravity?(cont.) • Weight is the gravitational force exerted on an object. • Near Earth’s surface, an object’s weight is the gravitational force exerted on the object by Earth. • Because weight is a force, it is measured in newtons. Lesson 1-2

18. What is gravity?(cont.) • An object’s weight is proportional to its mass. • Near Earth’s surface, the weight of an object in newtons is about ten times its mass in kilograms. Lesson 1-2

19. Friction • Friction is a force that opposes the movement between two touching surfaces. • There are several types of friction. • static friction • sliding friction • fluid friction Lesson 1-3

20. Friction(cont.) static Science Use at rest or having no motion Common Use noise produced in a radio or television Lesson 1-3

21. Friction(cont.) • Static friction prevents surfaces from sliding past each other. • Up to a limit, the strength of static friction changes to match the applied force. • Sliding friction opposes the motion of surfaces sliding past each other. Lesson 1-3

22. Friction(cont.) • Fluid friction is friction between a surface and a fluid—any material, such as water or air, that flows. • Fluid friction between a surface and air is air resistance. Lesson 1-3

23. Friction(cont.) • What causes friction between surfaces? • When the microscopic dips and bumps on one surface catch the dips and bumps on another surface, the microscopic roughness slows sliding. • This is a source of friction. Lesson 1-3

24. Friction(cont.) How does friction affect the motion of two objects sliding past each other? Lesson 1-3

25. Reducing Friction Lubricants decrease friction and with less friction, it is easier for surfaces to slide past each other. Lesson 1-3

26. Forces can be either contact, such as a karate chop, or noncontact, such as gravity. Each type is described by its strength and direction. Lesson 1 - VS

27. Gravity is an attractive force that acts between any two objects that have mass. The attraction is stronger for objects with greater mass. Lesson 1 - VS

28. Friction can reduce the speed of objects sliding past each other. Air resistance is a type of fluid friction that slows the speed of a falling object. Lesson 1 - VS

29. Which refers to gravitational force exerted on an object? A. contact force B. gravity C. mass D. weight Lesson 1 – LR1

30. Which is proportional to an object’s weight? A. gravitational force B. length C. mass D. noncontact force Lesson 1 – LR2

31. Which is a force that opposes the movement between two touching surfaces? A. net force B. lubricant C. gravity D. friction Lesson 1 – LR3

32. 1. You pull on objects around you with the force of gravity. 2. Friction can act between two unmoving, touching surfaces. Do you agree or disagree? Lesson 1 - Now

33. Newton’s First Law • What is Newton’s first law of motion? • How is motion related to balanced and unbalanced forces? • What effect does inertia have on the motion of an object? Lesson 2 Reading Guide - KC

34. Newton’s First Law • net force • balanced forces • unbalanced forces • Newton’s first law of motion • inertia Lesson 2 Reading Guide - Vocab

35. Identifying Forces • The sum of all the forces acting on an object is the net force. • The net force depends on the directions of the forces applied to an object. • Because forces have direction, you have to specify a reference direction when you add forces. Lesson 2-1

36. Identifying Forces(cont.) • A force moving in the reference direction is positive, and a force in the opposite direction is negative. • When the forces applied to an object act in the same direction, the net force is the sum of the individual forces. Lesson 2-1

37. Identifying Forces(cont.) • When forces act in opposite direction on an object, the net force is still the sum of the forces. • The net force is the sum of the positive and negative forces. Lesson 2-1

38. Identifying Forces(cont.) • Balanced forces are forces that combine and form a net force of zero. • Forces that combine and form a net force that is not zero are unbalanced forces. Lesson 2-1

39. Newton’s First Law of Motion • According to Newton’s first law of motion, if the net force on an object is zero, an object at rest will stay at rest, and a moving object will continue moving in a straight line with constant speed. • As a result, balanced forces and unbalanced forces have different results when they act on an object. Lesson 2-2

40. Newton’s First Law of Motion(cont.) What is Newton’s first law of motion? Lesson 2-2

41. Newton’s First Law of Motion(cont.) • Balanced forces acting on an object do not change the object’s speed and direction. • Newton’s first law of motion only applies to balanced forces acting on an object. • When unbalanced forces act on an object, the object’s velocity changes. Lesson 2-2

42. Newton’s First Law of Motion(cont.) How is motion related to balanced and unbalanced forces? Lesson 2-2

43. Newton’s First Law of Motion(cont.) The tendency of an object to resist a change in its motion is called inertia. inertia from Latin iners, means “without skill, inactive” Lesson 2-2

44. Newton’s First Law of Motion(cont.) What effect does inertial have on the motion of an object? Lesson 2-2

45. Why do objects stop moving? • For an object to start moving, a force greater than static friction must be applied to it. • To keep an object in motion, a force at least as strong as friction must be applied continuously. • Objects stop moving because friction or another force acts on them. Lesson 2-3

46. Unbalanced forces cause an object to move. • According to Newton’s first law of motion, if the net force on an object is zero, the object’s velocity does not change. • Inertia is a property that resists a change in the motion of an object. Lesson 2 - VS

47. Which refers to forces that combine and form a net force that is not zero? A. balanced forces B. inertia C. net force D. unbalanced forces Lesson 2 – LR1

48. Which could cause an object to stop moving? A. friction B. inertia C. unbalanced forces D. velocity Lesson 2 – LR2

49. When equal forces act on an object in opposite directions, what is the net force on the object? A. zero B. one C. equal D. balanced Lesson 2 – LR3

50. Do you agree or disagree? 3. Forces acting on an object cannot be added. 4. A moving object will stop if no forces act on it. Lesson 2 - Now