2. Unit 2: Motion & Forces Newton’s Laws of Motion “If I have seen far, it is because I have stood on the shoulders of giants.” - Sir Isaac Newton (referring to Galileo)

3. Motion & Forces Ch 1. Describing Motion  Motion  Speed & Velocity  Acceleration

4. Newton’s First Law Newton’s First Law of Motion  An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force. motion constant velocity net force

5. A. Motion Problem:  Is your desk moving? We need a reference point...  nonmoving point from which motion is measured

6. A. Motion Motion  Change in position in relation to a reference point. Reference point Motion

7. A. Motion Problem: You are a passenger in a car stopped at a stop sign. Out of the corner of your eye, you notice a tree on the side of the road begin to move forward. You have mistakenly set yourself as the reference point.

8. B. Speed & Velocity Speed  rate of motion  distance traveled per unit time v d t

9. B. Speed & Velocity Instantaneous Speed  speed at a given instant Average Speed

10. B. Speed & Velocity Problem:  A storm is 10 km away and is moving at a speed of 60 km/h. Should you be worried?  It depends on the storm’s direction!

11. B. Speed & Velocity Velocity  speed in a given direction  can change even when the speed is constant!

12. C. Acceleration Acceleration  the rate of change of velocity  change in speed or direction a: acceleration v f : final velocity v i : initial velocity t: time a v f - v i t

13. C. Acceleration Positive acceleration  “speeding up” Negative acceleration  “slowing down”

14. D. Calculations Your neighbor skates at a speed of 4 m/s. You can skate 100 m in 20 s. Who skates faster? GIVEN: d = 100 m t = 20 s v = ? WORK : v = d ÷ t v = (100 m) ÷ (20 s) v = 5 m/s You skate faster! v d t

15. D. Calculations A roller coaster starts down a hill at 10 m/s. Three seconds later, its speed is 32 m/s. What is the roller coaster’s acceleration? GIVEN: v i = 10 m/s t = 3 s v f = 32 m/s a = ? WORK : a = ( v f - v i ) ÷ t a = (32m/s - 10m/s) ÷ (3s) a = 22 m/s ÷ 3 s a = 7.3 m/s 2 a v f - v i t

16. D. Calculations Sound travels 330 m/s. If a lightning bolt strikes the ground 1 km away from you, how long will it take for you to hear it? GIVEN: v = 330 m/s d = 1km = 1000m t = ? WORK : t = d ÷ v t = (1000 m) ÷ (330 m/s) t = 3.03 s v d t

17. D. Calculations How long will it take a car traveling 30 m/s to come to a stop if its acceleration is -3 m/s 2 ? GIVEN: t = ? v i = 30 m/s v f = 0 m/s a = -3 m/s 2 WORK : t = ( v f - v i ) ÷ a t = (0m/s-30m/s)÷(-3m/s 2 ) t = -30 m/s ÷ -3m/s 2 t = 10 s a v f - v i t

18. E. Graphing Motion slope = steeper slope = straight line = flat line = Distance-Time Graph A B faster speed constant speed no motion speed

19. E. Graphing Motion Who started out faster?  A (steeper slope) Who had a constant speed? AA Describe B from 10-20 min.  B stopped moving Find their average speeds.  A = (2400m) ÷ (30min) A = 80 m/min  B = (1200m) ÷ (30min) B = 40 m/min Distance-Time Graph A B

20. E. Graphing Motion Acceleration is indicated by a curve on a Distance-Time graph. C h a n gi n g sl o p e = c h a n gi n g v el o ci ty

21. E. Graphing Motion Speed-Time Graph slope = straight line = flat line = acceleration  +ve = speeds up  -ve = slows down constant accel. no accel. (constant velocity)

22. E. Graphing Motion Speed-Time Graph Specify the time period when the object was... slowing down  5 to 10 seconds speeding up  0 to 3 seconds moving at a constant speed  3 to 5 seconds not moving  0 & 10 seconds

23. Bell Ringer What is Speed? What is Acceleration?

24. Motion & Forces Ch 1. Defining Force  Force  Newton’s First Law  Friction

25. A. Force Force  a push or pull that one body exerts on another  What forces are being exerted on the football? F kick F grav

26. A. Force Has the ability to change an objects motion:  Starting  Stopping  Speeding up  Slowing down  Changing direction

27. A. Force May change an object’s shape Forces give energy to an object All of the forces acting on an object together are known as net forces

28. A. Force Forces can be represented with arrows called vectors.  Vectors show the direction and magnitude of a force Forces are measure in Newtons (N)  https://youtu.be/bOIe0DIMbI8

29. A. Force Balanced Forces  forces acting on an object that are opposite in direction and equal in size  no change in velocity

30. A. Force Unbalanced Forces  unbalanced forces that are not opposite and equal  velocity changes (object accelerates) F friction W F pull F net NN

31. Bell Ringer What is a Force? What unit is force measure in? What is a vector?

32. B. Newton’s First Law Newton’s First Law of Motion  An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.

33. B. Newton’s First Law Newton’s First Law of Motion  “Law of Inertia” Inertia  tendency of an object to resist any change in its motion  increases as mass increases

34. B. Newton’s First Law Objects do not change their motion unless a force acts on them  An object will NOT start moving unless a force acts on it  An object will NOT stop moving unless a force acts on it.

35.  An object will NOT change speed unless a force acts on it  An object will NOT change direction unless a force acts on it.  The more mass an object has, the more inertia it has. This means that more mass an object has the harder it is to move, stop, or change the speed or direction of the object.

36. http://www.physicsclassroom.com/mmedia/newtlaws/cci.cfm Don’t let this be you. Wear seat belts! Because of inertia, objects (including you) resist changes in their motion. When the car going 80 km/ hour is stopped by the brick wall, your body keeps moving at 80 m/hr.

37. C. Friction Friction  force that opposes motion between 2 surfaces  depends on the: types of surfaces force between the surfaces

38. C. Friction Friction is greater...  between rough surfaces  when there’s a greater force between the surfaces (e.g. more weight) Pros and Cons?

39. Bell Ringer What is friction? What two things affect friction?

40. Review

41. Motion & Forces Ch 2. Force & Acceleration  Newton’s Second Law  Gravity  Calculations

42. A. Newton’s Second Law Newton’s Second Law of Motion  The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. F = ma

43. A. Newton’s Second Law F = ma F:force (N) m:mass (kg) a:accel (m/s 2 ) 1 N = 1 kg ·m/s 2 m F a F m

44. B. Gravity Gravity  force of attraction between any two objects in the universe  increases as... mass increases distance decreases

45. B. Gravity Who experiences more gravity - the astronaut or the politician? less distance more mass Which exerts more gravity - the Earth or the moon?

46. B. Gravity Weight  the force of gravity on an object MASS always the same (kg) WEIGHT depends on gravity (N) W = mg W:weight (N) m:mass (kg) g:acceleration due to gravity (m/s 2 )

47. B. Gravity Would you weigh more on Earth or Jupiter? greater gravity greater weight greater mass  Jupiter because...

48. Bell Ringer What is gravity? What unit of measurement is force measured in? What are the units for: velocity, acceleration, distance, mass?

49. C. Calculations What force would be required to accelerate a 40 kg mass by 4 m/s 2 ? GIVEN: F = ? m = 40 kg a = 4 m/s 2 WORK : F = ma F = (40 kg)(4 m/s 2 ) F = 160 N m F a

50. C. Calculations A 4.0 kg shotput is thrown with 30 N of force. What is its acceleration? GIVEN: m = 4.0 kg F = 30 N a = ? WORK : a = F ÷ m a = (30 N) ÷ (4.0 kg) a = 7.5 m/s 2 m F a

51. C. Calculations Ms. S. weighs 557 N. What is her mass? GIVEN: F(W) = 557 N m = ? a( g ) = 9.8 m/s 2 WORK : m = F ÷ a m = (557 N) ÷ (9.8 m/s 2 ) m = 56.8 kg m F a

52. ConcepTest Is the following statement true or false?  An astronaut has less mass on the moon since the moon exerts a weaker gravitational force.  False! Mass does not depend on gravity, weight does. The astronaut has less weight on the moon.

53. Motion & Forces Ch 3. Action and Reaction  Newton’s Third Law  Momentum  Conservation of Momentum

54. A. Newton’s Third Law Newton’s Third Law of Motion  When one object exerts a force on a second object, the second object exerts an equal but opposite force on the first.

55. A. Newton’s Third Law Problem:  How can a horse pull a cart if the cart is pulling back on the horse with an equal but opposite force? NO!!!  Aren’t these “balanced forces” resulting in no acceleration?

56. A. Newton’s Third Law  forces are equal and opposite but act on different objects  they are not “balanced forces”  the movement of the horse depends on the forces acting on the horse Explanation:

57. A. Newton’s Third Law Action-Reaction Pairs The hammer exerts a force on the nail to the right. The nail exerts an equal but opposite force on the hammer to the left.

58. A. Newton’s Third Law Action-Reaction Pairs The rocket exerts a downward force on the exhaust gases. The gases exert an equal but opposite upward force on the rocket. FGFG FRFR

59. A. Newton’s Third Law Action-Reaction Pairs Both objects accelerate. The amount of acceleration depends on the mass of the object. F m Small mass  more acceleration Large mass  less acceleration

60. Examples As a man exits a canoe, the canoe moves in the opposite direction. The canoe has an equal and opposite reaction to the man’s action. As the paddle is pushed backward in the water the canoe moves forward A swimmer pushes water back with his arms, but his body moves forward.

61. JET CAR CHALLENGE CHALLENGE: Construct a car that will travel as far as possible (at least 3 meters) using only the following materials. scissors tape 4 plastic lids 2 skewers 2 straws 1 balloon 1 tray How do each of Newton’s Laws apply?

62. B. Momentum Momentum  quantity of motion p = mv p:momentum (kg ·m/s) m:mass (kg) v:velocity (m/s) m p v

63. B. Momentum Find the momentum of a bumper car if it has a total mass of 280 kg and a velocity of 3.2 m/s. GIVEN: p = ? m = 280 kg v = 3.2 m/s WORK : p = mv p = (280 kg)(3.2 m/s) p = 896 kg·m/s m p v

64. B. Momentum The momentum of a second bumper car is 675 kg·m/s. What is its velocity if its total mass is 300 kg? GIVEN: p = 675 kg·m/s m = 300 kg v = ? WORK : v = p ÷ m v = (675 kg·m/s)÷(300 kg) v = 2.25 m/s m p v

65. C. Conservation of Momentum Law of Conservation of Momentum  The total momentum in a group of objects doesn’t change unless outside forces act on the objects. p before = p after

66. C. Conservation of Momentum Elastic Collision  KE is conserved Inelastic Collision  KE is not conserved

67. A. Newton’s First Law Newton’s First Law of Motion  An object at rest will remain at rest and an object in motion will continue moving at a constant velocity unless acted upon by a net force.

68. B. Newton’s Second Law Newton’s Second Law of Motion  The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass. F = ma

69. C. Newton’s Third Law Newton’s Third Law of Motion  When one object exerts a force on a second object, the second object exerts an equal but opposite force on the first.