Science Grade 8 Topic 3 Lesson 1 Pages 120-123

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by Khresto MAS0 views·Updated Oct 27, 2020
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  1. Hello, Eighth graders.
  2. How are you today?
  3. We're going to be starting with Topic three forces in
  4. motion. Lesson one describing Motion and force.
  5. We're going to be working on pages.
  6. 120 to 123 in your text.
  7. Okay, so any object that is moving is an object
  8. that is in motion.
  9. Okay, All objects that move have a starting point.
  10. For example, if you get in your car and start
  11. going, your starting point is usually your garage or your
  12. parking spot wherever you parked.
  13. That is your starting point.
  14. Now, when things whole topic is this whole lesson is
  15. going to be about describing motion describing force.
  16. When we want to describe how something moves we have
  17. Thio, we have to choose a reference point which pretty
  18. much means like where were were.
  19. Where will we be looking at it from?
  20. Okay, we'll be.
  21. Will we be in the car?
  22. Who will we be outside?
  23. Will we be in a car that's next to it?
  24. Will we be on the sidewalk?
  25. So the reference point is very, very important.
  26. So the reference point is a point that all motion
  27. will be measured relative to the starting point.
  28. So, for example, I'm, for example, if I'm on the
  29. sidewalk and I'm looking at a car moving, okay, I
  30. will have the same the same vision of the car
  31. moving. I won't be able to describe it in the
  32. same way as a person that's sitting in the car.
  33. Okay, so it all depends on the reference point.
  34. So motion is actually relative because it depends on the
  35. reference point.
  36. Okay, So when we're looking at this train, okay, at
  37. this boy that's sitting on that standing, you should be
  38. a standing but a boy standing still on a train.
  39. Now, from where we're looking at from the way that
  40. we're looking at it from our screen, it looks like
  41. the train is moving from left to right.
  42. And from our frame of reference, the boys moving from
  43. left to right.
  44. But what if somebody stood on the other side?
  45. What would they see?
  46. Right of somebody was standing right next to the boy.
  47. What would they see?
  48. Okay, So if you're standing right next to the boy,
  49. you know, the train is just moving straight.
  50. We're looking at it.
  51. It looks like it's moving from left to right on
  52. the other side.
  53. It way would see the opposite direction.
  54. Okay, so that's what they need by motion is relative
  55. motion is relative to the reference point to where you're
  56. looking at things.
  57. Okay, so this is unexamined.
  58. All of that kind of explains the That kind of
  59. demonstrates what we were.
  60. What? I was just talking about the cars.
  61. So if we're looking at it from this guy, that's,
  62. uh, that's the guy that's closer to us.
  63. It shows he can see that the car is moving
  64. to the left.
  65. Okay. The other side.
  66. See that the car is moving to the right.
  67. So if we asked for a description of the motion
  68. from these two people, they will give us a different
  69. description because motion is relative to the reference point.
  70. They're two different reference points, and so there are two
  71. different descriptions.
  72. Okay, so we're going to talk about how forces affect
  73. motion. Okay, So what is a force?
  74. A force is a push or a pull on an
  75. object. Okay.
  76. It's not necessarily as you know, as illustrated or as,
  77. um as literal as this picture as a zit looks
  78. like in the picture.
  79. Okay? Like, push and pull Its Not necessarily it.
  80. It could be a person.
  81. It could be the mass of an object.
  82. A weight of an object.
  83. Okay. It could be gravity.
  84. It could be, um Okay, so we said that it
  85. could be gravity.
  86. When you're when you're moving your chair back, you're exerting
  87. a force on it.
  88. When you are grabbing your book back, you're exerting a
  89. force you're pulling it boards your muscles exert forces on
  90. each other when they relax and contract.
  91. And that's how they move.
  92. Okay, so as we know, everything has a unit.
  93. Okay, so the unit of force The Standard Excuse me,
  94. The international system of units, you know, of course, is
  95. a Newton.
  96. Okay, Newton.
  97. Now, when we're trying to describe force, uh, you know,
  98. now we're going to begin with physics, and I'm sure
  99. you've taken this in math, but we usually there's always
  100. a way to represent things.
  101. When we're representing force, we're going to be used a
  102. force arrow.
  103. All right, so the forest arrow has a direction, okay?
  104. It has a direction, and it has a length.
  105. Okay, So the length of the arrow shows you the
  106. magnitude or the amount of of force, which is like,
  107. How many Newtons there are there?
  108. Like they're five or 10 Newtons, three to whatever it
  109. is the amount, the amount of force.
  110. Excuse me.
  111. The length of the arrow depends on the amount of
  112. force. And the direction the arrow is in is the
  113. direction of the force.
  114. All right, So, for example, over here, the force arrow
  115. on the top is shorter than the one on the
  116. bottom. Okay, so the black horse arrow is much shorter
  117. than the Red Horse arrow.
  118. They're both going in the same direction.
  119. So the forces both going is going in the same
  120. direction for both of them.
  121. But the force on the top is much less than
  122. the force on the bottom.
  123. Okay, so the Red Force, for example, could be 10
  124. Newtons and the Black Force could be five Newtons, for
  125. example. Okay, so I hope that this, um that this
  126. video was very helpful.
  127. And I will see you guys next time