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# Dynamics (motion)

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### Dynamics (motion)

1. 1. Dynamics
2. 2. Dynamics is the study of things that move, and why they move. fire extinguisher momentum.mpeg
4. 5. Basic equation
5. 8. <ul><li>The motorcycle was traveling at 250 km/h. </li></ul><ul><li>Convert this to ms -1 </li></ul><ul><li>“ See- think- react” usually takes 1 second. </li></ul><ul><li>How far does the rider travel? </li></ul>
6. 9. <ul><li>the bike rider was found INSIDE the car. </li></ul><ul><li>The Volkswagen actually flipped over from the force of impact and landed 3 m from where the collision took place.   </li></ul>
7. 10. Acceleration equation
8. 11. Kinematic Equations
9. 13. Displacement/time Graphs stationary d t
10. 14. Moving forward constant velocity d t
11. 15. <ul><li>Displacement Time Graph </li></ul>d constant Velocity (R) constant Velocity (L) STOP constant Velocity (L) constant Velocity (R) STOP t stopped
12. 16. For a displacement/time graph <ul><li>Positive slope means moving to the </li></ul>Negative slope means moving to the right left
13. 17. Gradient = Rise Run = Δ d = velocity Δ t Δ d Δ t d t
14. 18. d t d d t t Constant gradient Constant velocity Increasing gradient acceleration Decreasing gradient decceleration
15. 19. acceleration d t
16. 20. decceleration d t
17. 21. <ul><li>Velocity/Time Graphs </li></ul>V t Increasing V constant V decreasing V Increasing V decreasing V
18. 22. Positive velocity : Moving to the right accelerating deccelerating constant velocity Negative velocity : Moving to the left deccelerating accelerating v t
19. 23. Positive area, moving to the right Negative area, moving to the left
20. 24. Gradient = Rise Run = Δ v = acceleration Δ t Δ v Δ t v t
21. 25. Scalars and Vectors Scalars have only size Distance Speed Vectors have size and direction Displacement m Velocity ms -1 Acceleration ms -2 Force N
22. 26. Vectors <ul><li>Adding Vectors. </li></ul><ul><li>When is 3 + 3 not equal to 6? </li></ul><ul><li>Courtney rides 3 km north then 3 km south . </li></ul><ul><li>What is her displacement? </li></ul><ul><li>In this case 3 + 3 = 0 if you take into account direction. </li></ul>
23. 27. <ul><li>Sarah rides 3 km north then 3 km east. </li></ul><ul><li>What is her displacement? </li></ul>Displacement is Direction is 045 0
24. 28. <ul><li>So you can see that to ADD vectors, you put them tail to head. </li></ul><ul><li>The total is from tail to head </li></ul>A B To find A + B A + B
25. 29. <ul><li>The order doesn’t matter </li></ul>A B To find A + B A + B
26. 30. Adding Forces <ul><li>What size is the total (net) force? </li></ul>300 N 300 N
27. 31. <ul><li>What size is the total (net) force? </li></ul>600 N 300 N
28. 32. Find the Net Force 90 0 300 000N 300 000N
30. 34. Adding Velocities <ul><li>Jess is walking at 3.0 ms -1 in the bus. </li></ul><ul><li>The bus is moving at 4.0 ms -1 </li></ul><ul><li>What is her velocity if….. </li></ul>
31. 35. Adding Velocities <ul><li>Jess is walking at 3.0 ms -1 in the bus. </li></ul><ul><li>The bus is moving at 4.0 ms -1 </li></ul><ul><li>What is her velocity if….. </li></ul>
32. 36. Adding Velocities <ul><li>Jess is walking at 3.0 ms -1 in the bus. </li></ul><ul><li>The bus is moving at 4.0 ms -1 </li></ul><ul><li>What is her velocity if….. </li></ul>
33. 37. <ul><li>A plane is pointing north with an airspeed of 400 kmh -1 . </li></ul><ul><li>The wind is from the west at 300 kmh -1 . </li></ul><ul><li>What is the plane’s ground velocity? </li></ul>
34. 38. Plane in still air Plane pushed by wind.
35. 39. Plane/air Wind/ground plane/ground Speed = θ
36. 40. River and Boat
37. 41. What direction must the plane point so it flies north ?
38. 42. Plane/air Wind/ground plane/ground
39. 43. Plane/air Wind/ground plane/ground φ What is the speed? What direction does the pilot point?
40. 44. Change in Velocity <ul><li>The change in anything is what it is minus what it was . </li></ul><ul><li>Confused???????? </li></ul><ul><li>What is the change in your height in the last 5 years? </li></ul><ul><li>Height change= height now – height then </li></ul>
41. 45. <ul><li>You had \$5 yesterday now you have \$10 </li></ul><ul><li>What is the change in your wealth? </li></ul><ul><li>You had \$10 yesterday now you have \$5 </li></ul><ul><li>What is the change? </li></ul><ul><li>You had \$5 yesterday now you owe \$10 </li></ul><ul><li>What is the change? </li></ul>
42. 46. V i = 5 ms -1 What is the ball’s change in velocity? V f = 0 ms -1
43. 47. 5 ms -1 3 ms -1 What is the ball’s change in velocity?
44. 48. v i v f -v i v f Δ v
45. 49. Velocity change What direction is the force of the floor on the ball? Velocity change and force are in the same direction force
46. 50. <ul><li>What is the velocity change if the ball hits on an angle? </li></ul>-v i v f Δ v -v i v f v i v f
47. 51. Components <ul><li>We have seen that you add vectors tail to head . </li></ul>
48. 52. <ul><li>You can also separate a vector into two parts at right angles. </li></ul><ul><li>The parts are called components . </li></ul>OR
49. 53. The force from the rope can be split into two components The horizontal component pulls her forward The vertical component tries to lift her.
50. 54. Force <ul><li>A force is a </li></ul><ul><li>Newton’s First Law. </li></ul><ul><li>If F net = 0, </li></ul><ul><li>If F net = 0 </li></ul>push or a pull object is at rest or constant velocity object accelerates
51. 55. A Force Can Make Things Accelerate
52. 57. Adding Forces Thrust force Drag force What is the nett force? Nett force The car accelerates to the right
53. 58. Adding Forces Thrust force Drag force What is the nett force? Nett force The car slows down
54. 59. If Fnet is in the same direction as the motion, car accelerates velocity F net If Fnet is in the opposite direction to the motion, car deccelerates velocity F net
55. 60. Newton’s First Law <ul><li>“ Things like to keep doing what they are doing” </li></ul><ul><li>Or </li></ul><ul><li>“ an object moves at constant velocity unless an unbalanced force acts on it” </li></ul>
56. 64. <ul><li>F net = m x a </li></ul>a N kg ms -2 Bigger force. Bigger acceleration Bigger mass. Smaller acceleration v t
57. 65. Which accelerates most? F F F F Which accelerates most?
58. 66. If an object is dropped, (no air resistance) it accelerates downwards gaining 10 ms -1 every second F g = m x a Weight Force (N) mass (kg) acceleration (10 ms -2 ) g = 10 ms -2
59. 67. As an object falls, the air resistance increases F g F g F up F g F up F net = 0 (a = o) Constant velocity (terminal velocity) F g > F up so F net is down Still accelerates, but acceleration gets smaller
60. 68. Newton’s Third Law <ul><li>For every action force , </li></ul><ul><li>There is an equal and opposite reaction force </li></ul><ul><li> Acting on a different body </li></ul>Action force (on face) Reaction force (on ball)
61. 69. Or….you can’t touch without being touched… Force of Annie on Betty Force of Betty on Annie
62. 70. Action force (on wall) Reaction force (on wolfie)
63. 73. Action force Reaction force
64. 75. ACTION REACTION
65. 77. Balloon Rocket Action force (balloon on air) Reaction force (air on balloon)
66. 78. Rocket man & summary -
67. 80. Momentum
68. 81. Momentum is a vector quantity
69. 83. Impulse <ul><li>Describe how you catch an egg to minimise the chance of it breaking. </li></ul><ul><li>The damage to the egg (force on it) doesn’t just depend on how fast it’s travelling, but also how fast it stops . </li></ul>
70. 84. This is called IMPULSE
71. 85. If you jump out a window and hit the ground, your momentum changes. If you hit concrete, your momentum changes quickly ( Δ t is small, F is large) If you hit a trampoline, your momentum changes slowly ( Δ t is large, F is small)
72. 86. If you drive a car into a wall, its momentum changes. If the car is rigid, its momentum changes quickly ( Δ t is small, Force is large) If the car crumples, its momentum changes slowly ( Δ t is large, Force is small)
73. 87. <ul><li>Road Safety Message </li></ul><ul><li>The Faster you Go the Bigger the Mess! </li></ul>The Faster you Stop the Bigger the Mess!
74. 88. <ul><li>Would you rather fall 4 m onto concrete, or 8m into water? Explain. </li></ul>