Chapter Menu

1. Chapter Introduction Lesson 1 Newton’s First Law Lesson 2 Gravity and Friction 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 • mass • weight • friction • force • contact force • noncontact force • gravity Lesson 1 Reading Guide - Vocab

8. Newton’s First Law of Motion • According to Newton’s first law of motion, an object at rest will stay at rest, and an object in motion will continue moving unless acted upon by an unbalanced force. Lesson 2-2

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. Identifying Forces(cont.) • Balanced forces forces on an object that are equal in size and opposite in direction . Net force = 0Do not cause motion. • Forces that combine and form a net force >zero are unbalanced forces. Cause motion. Lesson 2-1

11. 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

12. 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. Lesson 1-1

13. Types of Forces(cont.) • Can you think of an example of a contact force? • Can you think of an example of a noncontact force? Lesson 1-1

14. Contact: Pushing a book off of a table • Noncontact: Gravity or magnetic forces

15. Agree or Disagree: A moving object will stop if there are no forces acting on it? • Think About it: If you kick a soccer ball across a field will it go on forever? • What forces will cause it to stop? • If there where no forces acting on it (friction, gravity, walls, people) would the soccer ball continue to move?

16. 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

17. 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

18. Inertia- the tendency of an object to resist changes in motion • Examples… • An object with less mass has less inertia and an object with more mass has more inertia • Can you think of any examples?

19. Types of Forces(cont.) • Is it easier to throw a baseball or a bowling ball? Explain why. • Explain which has greater inertia: a jet plane sitting on the runway or a speeding car? Lesson 1-1

20. 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

21. Unbalanced forces cause an object to speed up, slow down, or change direction. Lesson 3 - VS

22. 2 Gravity and Friction • Friction and gravity are two forces that can change the motion of an object. • 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

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

24. Lesson 1-3 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. Friction(cont.)

25. Lesson 1-3 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. Friction(cont.)

26. 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. The greater the surface area of an object, the more air resistance it will experience. Lesson 1-3 Friction(cont.)

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

28. Lubricants decrease friction and with less friction, it is easier for surfaces to slide past each other. What reduces friction between a door and a hinge? What reduced friction between two bones in a joint? Reducing Friction Lesson 1-3

29. Increasing Friction How would you increase the friction between your foot and the ice on the sidewalk?

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

31. 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. What is gravity?(cont.) Lesson 1-2

32. 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. What is gravity?(cont.) Lesson 1-2

33. 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. What is gravity?(cont.) Lesson 1-2

34. An object’s weight is proportional to its mass. Near Earth’s surface, the weight of an object in newtons is about ten times (9.8x) its mass in kilograms. What is gravity?(cont.) Lesson 1-2

35. 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

36. 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

37. 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.

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

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

40. 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

41. A push or a pull is called a? A. Gravity B. Newton C. Force D. Motion Lesson 1 – LR2

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

43. Which refers to forces that combine and form a net force that is greater than zero? A. balanced forces B. inertia C. net force D. unbalanced forces Lesson 2 – LR1

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

45. 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

46. Do you agree or disagree? • 2. Friction can act between two unmoving, touching surfaces. • Agree • Forces acting on an object cannot be added. • Disagree Lesson 2 - Now

47. Newton’s Second Law • What is Newton’s second law of motion? • How does centripetal force affect circular motion? Lesson 3 Reading Guide - KC

48. How do forces change motion? • Forces change an object’s motion by changing its speed, its direction, or both its speed and its direction. • Velocity is speed in a certain direction. • Only unbalanced forces change an object’s velocity. • Unbalanced forces make an object accelerate by changing its speed, its direction, or both. Lesson 3-1

49. Acceleration—Changes in Velocity • Acceleration is a measure of how much the velocity of an object changes in a unit of time. • An object accelerates when its velocity changes as a result of increasing speed, decreasing speed, or a change in direction. Lesson 3-1

50. How do forces change motion?(cont.) • When unbalanced forces act on an object at rest, the object begins moving • in the same direction of the net force. • If the net force acting on a moving object is in the same direction that the object is moving • the object will speed up. • If the direction of the net force on an object is opposite to the direction the object moves • the object slows down. Lesson 3-1