1. Chapter 20 Forces and Motion Preview Section 1 Gravity and MotionGravity and Motion Section 2 Newton’s Laws of MotionNewton’s Laws of Motion Section 3 MomentumMomentum Concept Mapping

2. Chapter 20 Bellringer Answer the following questions in your science journal: If Wile E. Coyote and a boulder fall off a cliff at the same time, which do you think will hit the ground first? Would it matter if the cliff were very high or particularly low? How could Mr. Coyote slow down his fall? Section 1 Gravity and Motion

3. Chapter 20 Objectives Explain the effect of gravity and air resistance on falling objects. Explain why objects in orbit are in free fall and appear to be weightless. Describe how projectile motion is affected by gravity. Section 1 Gravity and Motion

4. Chapter 20 Gravity and Falling Objects Gravity and Acceleration Objects fall to the ground at the same rate because the acceleration due to gravity is the same for all objects. Acceleration Due to Gravity As shown on the next slide, for every second that an object falls, the object’s downward velocity increases by 9.8 m/s. Section 1 Gravity and Motion

5. Chapter 20 Section 1 Gravity and Motion

6. Chapter 20 Gravity and Falling Objects, continued Velocity of Falling Objects You can calculate the change in velocity with the following equation: ∆v  g  t If an object starts at rest, this equation yields the velocity of the object after a certain time period. Section 1 Gravity and Motion

7. Chapter 20 Section 1 Gravity and Motion

8. Chapter 20 Air Resistance and Falling Objects Air resistance is the force that opposes the motion of objects through air. The amount of air resistance acting on an object depends on the size, shape, and speed of the object. The image on the next slide shows the effects of air resistance on a falling object. Section 1 Gravity and Motion

9. Chapter 20 Section 1 Gravity and Motion

10. Chapter 20 Air Resistance and Falling Objects, continued Acceleration Stops at the Terminal Velocity As the speed of a falling object increases, air resistance increases. The upward force of air resistance continues to increase until it is equal to the downward force of gravity. The object then falls at a constant velocity called the terminal velocity. Section 1 Gravity and Motion

11. Chapter 20 Air Resistance and Falling Objects, continued Free Fall Occurs When There Is No Air Resistance An object is in free fall only if gravity is pulling it down and no other forces are acting on it. A vacuum is a place in which there is no matter. Objects falling in a vacuum are in free fall because there is no air resistance. Section 1 Gravity and Motion

12. Chapter 20 Orbiting Objects Are in Free Fall Astronauts float in orbiting spacecrafts because of free fall. Two Motions Combine to Cause Orbiting An object is orbiting when it is traveling around another object in space. The image on the next slide describes how an orbit is formed. Section 1 Gravity and Motion

13. Chapter 20 Section 1 Gravity and Motion

14. Chapter 20 Orbiting Objects Are in Free Fall, continued Orbiting and Centripetal Force The unbalanced force that causes objects to move in a circular path is called a centripetal force. Gravity provides the centripetal force that keeps objects in orbit. Section 1 Gravity and Motion

15. Chapter 20 Projectile Motion and Gravity Projectile motion is the curved path an object follows when it is thrown or propelled near the surface of the Earth. Projectile motion has two components—horizontal motion and vertical motion. These components are independent, so they have no effect on each other. Section 1 Gravity and Motion

16. Chapter 20 Projectile Motion and Gravity, continued Horizontal Motion is a motion that is parallel to the ground. When you throw a ball, your hand exerts a force on the ball that makes the ball move forward. This force gives the ball its horizontal motion. Section 1 Gravity and Motion

17. Chapter 20 Projectile Motion and Gravity, continued Vertical Motion is motion that is perpendicular to the ground. A ball in your hand is prevented from falling by your hand. After you throw the ball, gravity pulls it downward and gives the ball vertical motion. Section 1 Gravity and Motion

18. Chapter 20 Section 1 Gravity and Motion

19. Chapter 20 Projectile Motion and Gravity Section 2 Newton’s Laws of Motion Click below to watch the Visual Concept. Visual Concept

20. Chapter 20 Bellringer Respond to the following question in your science journal: If you are sitting still in your seat on a bus that is traveling 100 km/h on a highway, is your body at rest or in motion? Explain your answer. Use a diagram if it will help make your answer clear. Section 2 Newton’s Laws of Motion

21. Chapter 20 Objectives Describe Newton’s first law of motion, and explain how it relates to objects at rest and objects in motion. State Newton’s second law of motion, and explain the relationship between force, mass, and acceleration. State Newton’s third law of motion, and give examples of force pairs. Section 2 Newton’s Laws of Motion

22. Chapter 20 Newton’s First Law of Motion An object at rest remains at rest, and an object in motion remains in motion at a constant speed and in a straight line unless acted on by an unbalanced force. Newton’s first law of motion describes the motion of an object that has a net force of 0 N acting on it. Section 2 Newton’s Laws of Motion

23. Chapter 20 Newton’s First Law of Motion, continued Part 1: Objects at Rest Objects at rest will stay at rest unless they are acted on by an unbalanced force. Part 2: Objects in Motion Objects will continue to move with the same velocity unless an unbalanced force acts on them. The image on the next slide shows how you can have fun with Newton’s first law. Section 2 Newton’s Laws of Motion

24. Chapter 20 Newton’s First Law of Motion, continued Section 2 Newton’s Laws of Motion

25. Chapter 20 Newton’s First Law of Motion, continued Friction and Newton’s First Law Friction between an object and the surface it is moving over is an example of an unbalanced force that stops motion. Inertia and Newton’s First Law Newton’s first law is sometimes called the law of inertia. Inertia is the tendency of all objects to resist any change in motion. Section 2 Newton’s Laws of Motion

26. Chapter 20 Newton’s First Law of Motion, continued Mass and Inertia Mass is a measure of inertia. An object that has a small mass has less inertia than an object that has a large mass. So, changing the motion of an object that has a small mass is easier than changing the motion of an object that has a large mass. Section 2 Newton’s Laws of Motion

27. Chapter 20 Newton’s Second Law of Motion The acceleration of an object depends on the mass of the object and the amount of force applied. Newton’s second law describes the motion of an object when an unbalanced force acts on the object. Section 2 Newton’s Laws of Motion

28. Chapter 20 Newton’s Second Law of Motion, continued Part 1: Acceleration Depends on Mass The acceleration of an object decreases as its mass increases. Its acceleration increases as its mass decreases. Part 2: Acceleration Depends on Force An object’s acceleration increases as the force on the object increases. The acceleration of an object is always in the same direction as the force applied. Section 2 Newton’s Laws of Motion

29. Chapter 20 Section 2 Newton’s Laws of Motion

30. Chapter 20 Newton’s Second Law of Motion, continued Expressing Newton’s Second Law Mathematically The relationship of acceleration (a) to mass (m) and force (F) can be expressed mathematically with the following equation: m a  F m, orF   a Section 2 Newton’s Laws of Motion

31. Chapter 20 Section 2 Newton’s Laws of Motion

32. Chapter 20 Click below to watch the Visual Concept. Newton’s Second Law of Motion, continued Visual Concept Section 2 Newton’s Laws of Motion

33. Chapter 20 Newton’s Third Law of Motion Whenever one object exerts a force on a second object, the second object exerts an equal and opposite force on the first. Newton’s third law of motion can be simply stated as follows: All forces act in pairs. Section 2 Newton’s Laws of Motion

34. Chapter 20 Newton’s Third Law of Motion, continued Force Pairs Do Not Act on the Same Object A force is always exerted by one object on another object. This rule is true for all forces, including action and reaction forces. Action and reaction forces in a pair do not act on the same object. If they did, the net force would always be 0 N and nothing would ever move! Section 2 Newton’s Laws of Motion

35. Chapter 20 Newton’s Third Law of Motion, continued All Forces Act in Pairs—Action and Reaction Newton’s third law says that all forces act in pairs. When a force is exerted, there is always a reaction force. Section 2 Newton’s Laws of Motion

36. Chapter 20 Newton’s Third Law of Motion, continued The Effect of a Reaction Can Be Difficult to See When an object falls, gravity pulls the object toward Earth and pulls Earth toward the object. You don’t notice Earth being pulled upward because the mass of Earth is much larger than the mass of the object. Thus, the acceleration of Earth is much smaller than the acceleration of the object. Section 2 Newton’s Laws of Motion

37. Chapter 20 Section 3 Momentum Bellringer This section is about momentum. Make a list of five things that have momentum and a list of five things that don’t have momentum. What must you do to give an object momentum? What about removing momentum? Explain your answers in your science journal.

38. Chapter 20 Objectives Calculate the momentum of moving objects. Explain the law of conservation of momentum. Section 3 Momentum

39. Chapter 20 Momentum, Mass, and Velocity The momentum of an object depends on the object’s mass and velocity. Calculating Momentum The relationship of momentum (p), mass (m), and velocity (v) is shown in the equation below: p  m x v Section 3 Momentum

40. Chapter 20 Section 3 Momentum

41. Chapter 20 The Law of Conservation of Momentum The law of conservation of momentum states that any time objects collide, the total amount of momentum stays the same. Objects Sticking Together After two objects stick together, they move as one object. The mass of the combined objects is equal to the masses of the two objects added together. Section 3 Momentum

42. Chapter 20 The Law of Conservation of Momentum, continued The combined objects have a different velocity because momentum is conserved and depends on mass and velocity. So, when the mass changes, the velocity must change, too. Section 3 Momentum

43. Chapter 20 The Law of Conservation of Momentum, continued Objects Bouncing Off Each Other When two objects bounce off each other, momentum is usually transferred from one object to the other. The transfer of momentum causes the objects to move in different directions at different speeds. Section 3 Momentum

44. Chapter 20 The Law of Conservation of Momentum, continued Conservation of Momentum and Newton’s Third Law Conservation of momentum can be explained by Newton’s third law. Because action and reaction forces are equal and opposite, momentum is neither gained or lost in a collision. Section 3 Momentum

45. Chapter 20 Forces and Motion Use the terms below to complete the concept map on the next slide. forceprojectile motion free fallair resistance terminal velocitygravity Concept Mapping

46. Chapter 20 Forces and Motion

47. Chapter 20 Forces and Motion