1. Review Question Define the term “force” in your own words. Force is a push or pull 1

2. Vocabulary Words-Force ForceFriction Static frictionKinetic Friction InertiaWeight Free fallMomentum Terminal Velocity Projectile Motion 2

3. DESCRIBE A SCENARIO WHEN FRICTION IS USEFUL. FRICTION IS ESSENTIAL WHEN YOU NEED TO STOP OR SLOW DOWN.

4. WHAT IS THE RELATIONSHIP BETWEEN FORCE AND MOTION?

5. 5 Standard SPS8 Determine the relationship among force, mass, and motion. b. Apply Newton’s three laws to everyday situations.

6. 6 Newton’s Laws of Motion

7. 7 Sir Isaac Newton 1642-1727 Described relationship between motion and force Newton’s laws of motion

8. 8 Newton’s 1 st Law of Motion An object at rest will remain at rest and an object in motion will remain in motion unless it experiences a net force.

9. 9 Can you describe some examples of Newton’s 1 st Law of Motion? http://www.physics.umd.edu/deptinfo/facilities/le cdem/services/demos/demosc3/c3-02.mpg http://www.physics.umd.edu/deptinfo/facilities/le cdem/services/demos/demosc3/c3-02.mpg

10. 10 Inertia The tendency of an object to remain at rest or remain in motion at a constant speed. Inertia depends on mass. (more mass = more inertia)

11. What is necessary to change the motion of an object? A Net Force must act on an object to change its motion.

12. Julie rides Acrophobia at Six Flags Over Georgia. As the seats begin to fall 16 stories, she feels as if she is floating. Use Newton’s 1 st Law to describe what is happening. Julie was at rest at the top of the ride. When the ride first starts falling, her body wants to remain at the top so she feels like she is floating.

13. 13 Newton’s 2 nd Law of Motion The acceleration of an object is directly proportional to the net force acting on it; and inversely proportional to its mass.

14. 14 Another way of saying it…. As mass increases, acceleration decreases (inversely proportional) As force increases, acceleration increases (directly proportional)

15. 15

16. 16 Units F = m x a kgx m/s 2 = Newton

17. 17 Practice #1 Zookeepers use a stretcher to lift a 175 kg sedated lion. If the upward acceleration of the lion and stretcher is 0.657 m/s 2, then what force is needed to lift the lion? G m = 175 kg a = 0.657 m/s 2 U F = ? E F = ma S F = (175 kg)(0.657 m/s 2 ) S F = 115 kg x m/s 2 115 N

18. 18 Practice #2 When a shot-putter exerts a force of 120.0 N on a shot, the shot accelerates at a rate of 19.0 m/s 2. What is the mass of the shot? G F = 120.0 N a = 19.0 m/s 2 U m = ? E m=F/a S m = 120.0 N /(19.0 m/s 2 ) S m = 6.32 kg

19. Practice Problems 19

20. Practice Problems 1. What net force is needed to accelerate a 1600 kg automobile forward at 2.0 m/s 2 ? GUESS 2. A baseball accelerates downward at 9.8 m/s 2. If the gravitational force is the only force acting on the baseball and is 1.4 N, what is the baseball’s mass? GUESS 3. A sailboat and its crew have a combined mass of 65 kg. If a net force of 895 N is pushing the sailboat forward, what is the sailboat’s acceleration? GUESS 4. The net forward force on the propeller of a 2.3 kg model airplane is 7.0 N. What is the acceleration of the plane? GUESS 20

21. 21 A.3 NB.4 N C.3 ND.No net force E.10 NF.8 N 1.3200 N2.0.14 kg 3.13.8 m/s 2 4.3.0 m/s 2

22. EQ: What determines how much an object speeds up or slows down as it experiences a net force? Mass & Acceleration

23. SP1. Analyze the relationship between force, mass, gravity, and the motion of objects.

24. If a Mack truck and a Volkswagen have a head on collision, which vehicle will experience the greater impact force? a)The Mack truck b)The Volkswagen c)Both the same d)…it depends on other factors

25. The answer will be revealed shortly…

26. Newton’s 3 rd Law of Motion When an object exerts a force on a second object, the second object exerts an equal and opposite force back onto the first object. Also known as “action-reaction” forces

27. Action-Reaction Forces For each “action” force name the “reaction” force Action: Ball hits bat. Reaction: Bat hits ball. Action: Ball pushes pin forward. Reaction: Pin pushes ball backward. Action: Athlete pushes barbell upward. Reaction: Barbell pushes athlete downward. Action: Air pushes balloon surface outward. Reaction: Balloon surface pushes air inward.

28. In other words… Forces come in pairs!

29. Can you identify at least 5 pair of action- reaction forces in the picture?

30. Now can you answer the question? If a Mack truck and a Volkswagen have a head on collision, which vehicle will experience the greater impact force? a) The Mack truck b) The Volkswagen c) Both the same d) …it depends on other factors * According to Newton’s 3 rd Law, forces are equal and opposite.

31. WHAT’S THE BIG IDEA? Newton’s First Law Newton’s Second Law Newton’s Third Law Inertia: Objects will continue their motion unless they experience a net force F=ma Acceleration is directly proportional to force. Acceleration is inversely proportional to mass. Action-Reaction force pairs For every force generated, there is another force of the same size acting in the opposite direction.

32. Summarize Newton’s Third Law: Action Reaction As mass acceleration _ As force acceleration _

33. If you drop a ball, it will fall towards Earth. A)What force causes this? B)B) Identify the action-reaction pair for this scenario. A)Gravity B)Earth pulls ball downward. Ball pulls Earth upward. Why then do you not see the Earth move upward? F=ma The earth has more mass, so it does not accelerate as much as the ball.

34. Standard 8. Determine the relationships among force, mass, and motion c.Relate falling objects to gravitational force d.Explain the difference between mass and weight

35. Gravity, Weight, & Mass

36. Mass The amount of matter in an object Weight depends on gravity, mass does not. The mass of an object is always the same, no matter the location.

37. Gravity A force that pulls objects together The larger the objects, the larger the force. (This is weight.) Objects fall towards the center of earth because of gravity.

38. In the absence of air resistance, all objects fall with a downward acceleration of 9.8 m/s 2 on Earth. This is acceleration due to gravity.

39. Weight The force on an object due to gravity To calculate weight: F w = ma g F = ma

40. Practice Problems 1.Convert your weight in pounds to Newtons using the conversion factor 9.8 N = 2.2 lbs. Ex: 100 lbs. x 9.8 N 1 2.2 lbs. = 980 N 2.2 = 445 N

41. Practice Problems 2.Calculate your mass. Ex: W = 445 N g = 9.8 m/s 2 m = ? m = W = 445 N g 9.8 m/s 2 = 45.4 kg

42. Practice Problems 3.How much would you weigh in Newtons on the moon where the acceleration due to gravity is 1.6 m/s 2 ? Gm = 45.4 kg g = 1.6 m/s 2 UW = ? EW = mg SW = (45.4 kg)(1.6 m/s 2 ) SW = 72.6 N

43. WHAT’S THE BIG IDEA? Weight vs Mass The same in all locations Dependent on gravity Force Measured in kg Measured in N Mass Weight Mass Weight

44. What is the difference between mass and weight?  Mass is the amount of matter (kg)  Weight is a force (N)

45. As an astronaut travels from the earth to space (where there is no gravity), her _________ will change. Her ________ will remain the same. mass weight

46. Air Resistance The force of air pushing up on a falling object. Opposite of weight Air Resistance Weight

47. Factors Affecting Air Resistance Speed of falling object Surface area of falling object

48. Terminal Velocity As an object falls faster, air resistance increases Eventually air resistance will equal objects weight Object will stop accelerating and continue to fall at a constant velocity (the terminal velocity)

49. Mass vs. Weight Double Bubble  Depends on Gravity  Kilograms  Newtons  Measure of matter  Force  Changes in different locations  Same in all locations  W = mg

50. EQ: If an elephant and a paper ball are dropped from the roof top at the same time, which will hit the ground first? They will hit the ground at the same time.

51. Describe the relationship between:  Force and acceleration: Directly Proportional  Mass and acceleration: Inversely Proportional  What is the rate of acceleration due to gravity? 9.8 m/s 2

52. Weight and mass are directly proportional. As mass increases, weight also increases. As mass decreases, weight also decreases.

53. a = (vf-vi) t F = ma W= mg ) F ma (vf-vi) ta m W g Fold your paper into 6 portions and write the key concepts for each of the following topics:  Weight  Mass  Friction  Newton’s 1 st  Newton’s 2 nd  Newton’s 3 rd

54. What equations have we used so far this semester?  Velocity (using slope)  Velocity  Acceleration  Force  Weight  EQ: What are the appropriate units for: slope = (y 2 -y 1 ) / (x 2 -x 1 ) v = d / t a = (v f – v i ) / t F = ma W = mg

55. Equations used so far... (vf-vi) ta F ma m W g (y 2 -y 1 ) slope (x 2 -x 1 ) d vt

56. What are the appropriate units for:  Velocity  Acceleration  Force  Weight  What’s next? ENERGY  Work  Power  Mechanical advantage  Simple machine  Compound machine  Energy  Potential energy  Kinetic energy  Mechanical energy  Efficiency m/s m/s 2 kg m / s 2 or N