Teoria relativităţii pe înţelesul tuturor - 1 — Transcript

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1. 0:04[Music]
2. 0:25oh
3. 0:27[Music]
4. 0:30oh
5. 0:33[Music]
6. 0:52[Music]
7. 1:36relativity Diana did you ever stop to be
8. 1:39amazed at how a GPS unit works not
9. 1:43really I got one for my birthday once
10. 1:46choser did you ever use one no never
11. 1:50needed one myself I always know where
12. 1:53I've been so I always know where I am
13. 1:57Kevin are you going to tell us how it
14. 1:59works
15. 2:01sure am it's a good intro into
16. 2:03relativity Jeeves want to take
17. 2:09over relativity is just a method for two
18. 2:12people to agree on what they see if one
19. 2:15of them is moving and since we all move
20. 2:17about pretty regularly we can find many
21. 2:19examples of how useful relativity is in
22. 2:22everyday life even if we don't call it
23. 2:24by
24. 2:26name one Miracle of Modern Life is the
25. 2:29global position system or GPS it is
26. 2:33pretty amazing that the GPS can pinpoint
27. 2:35your location anywhere on Earth to
28. 2:37within a few
29. 2:40yards and this magic depends entirely on
30. 2:43the existence of two dozen satellites
31. 2:4512,000 Mi above the Earth and a little
32. 2:49relativity briefly here's how it
33. 2:52works the GPS receiver gets a timing
34. 2:55signal from several different high-f
35. 2:57flying satellites and using Einstein's
36. 2:59theory of relativity it calculates the
37. 3:02distance from each satellite throw in a
38. 3:04little triangulation and out comes your
39. 3:07[Music]
40. 3:09location simple in
41. 3:11concept but to do this successfully the
42. 3:14timing signals must be accurate to a few
43. 3:17billionths of a
44. 3:19second so that the distance calculations
45. 3:22can be accurate to a few
46. 3:25yards but with all this motion going on
47. 3:28time and distance must be Recon outed
48. 3:30carefully without Einstein's version of
49. 3:33Relativity the accuracy of the global
50. 3:35positioning system would drift more than
51. 3:377 miles every
52. 3:42day but of course relativity was not a
53. 3:46New Concept with Einstein the problem of
54. 3:49how two people reconcile their
55. 3:50observations about the world if one of
56. 3:53them is moving has been addressed for
57. 3:57centuries let's ease our way into Rel it
58. 4:00with some common
59. 4:03[Music]
60. 4:06experiences if you are traveling in a
61. 4:09car on a smooth straight stretch of
62. 4:13highway there's no sensation of motion
63. 4:15at
64. 4:18all you mean I could read a book pour a
65. 4:22drink or flip a coin and everything
66. 4:24looks and feels the same as if the car
67. 4:26were sitting still
68. 4:30that's because relative to the car
69. 4:33you the
70. 4:35book the
71. 4:37drink and the
72. 4:39coin are not
73. 4:42moving notice that this works only if
74. 4:44the car is not changing direction or
75. 4:48speed so if the car accelerates or
76. 4:52turns pouring that drink becomes a real
77. 4:55problem but constant motion feels just
78. 4:59like sitting
79. 5:04still and if you want to know what it
80. 5:06feels like to move at 1,000 mph just
81. 5:09look around because of the Earth's spin
82. 5:13we zip along our time zone at a speedy
83. 5:151,000
84. 5:17mph and because of its motion around the
85. 5:19Sun the Earth carries us through space
86. 5:22about 67,000
87. 5:26mph and because of the motion of our
88. 5:29solar system about the center of our
89. 5:31galaxy we are moving at more than half a
90. 5:34million miles an hour but it's not
91. 5:37enough to ask how fast am I moving we
92. 5:41must ask how fast am I moving relative
93. 5:45to some other
94. 5:47[Music]
95. 5:55thing let's make up a simple rule that
96. 5:57allows two observers to agree on on how
97. 6:00fast something is
98. 6:02moving we begin at a moving walkway at
99. 6:05the
100. 6:08airport the walkway is moving at a Brisk
101. 6:113
102. 6:12mph so if Susan simply stands on the
103. 6:15walkway she is moving at 3 mph relative
104. 6:19to Sarah who is standing still but not
105. 6:22on the walkway
106. 6:28[Music]
107. 6:31if Susan walks on the walkway at 3 mph
108. 6:35she can accurately say she is walking at
109. 6:383
110. 6:39mph but Sarah sees her moving at 6
111. 6:43[Music]
112. 6:51mph and if Susan walks against the
113. 6:54walkway at 3
114. 6:56mph Susan can still say she's walking at
115. 6:593
116. 7:01mph but now Sarah sees her as standing
117. 7:05still 0 m hour so our first conclusion
118. 7:10is that two observers can simply add or
119. 7:12subtract their speed with respect to
120. 7:15each other to any measurement of
121. 7:17velocity they make this idea is the
122. 7:20basis of classical
123. 7:23relativity here's another
124. 7:25scenario suppose there's a Truck moving
125. 7:28down the road at a constant speed of 50
126. 7:33mph on the back are a baseball pitcher a
127. 7:38catcher and their pitching coach armed
128. 7:41with a speed
129. 7:42gun as long as the truck doesn't speed
130. 7:45up or slow down or hit any large bumps
131. 7:48they can conduct pitching practice just
132. 7:50the same as they would on the baseball
133. 7:52[Music]
134. 7:53field and when the pitcher throws a 100
135. 7:56mph fast ball
136. 7:59the coach's speed gun will read 100
137. 8:04mph the ball is indeed moving 100 mph
138. 8:08relative
139. 8:09to the pitcher the catcher the
140. 8:14coach and the
141. 8:18truck but suppose an observer standing
142. 8:20by the side of the road clocks the speed
143. 8:22of that same
144. 8:25baseball what speed would this Observer
145. 8:28measure for the ball
146. 8:31well the ball would already be moving at
147. 8:3350 mph when the pitcher was just holding
148. 8:37it so this Observer would measure a
149. 8:40speed of 150 mph for the
150. 8:43pitch the speed of the ball relative to
151. 8:46the
152. 8:48truck plus the speed of the truck
153. 8:51relative to The Observer
154. 8:54[Music]
155. 8:59this seems pretty easy early scientists
156. 9:02just needed to visit an airport or play
157. 9:05baseball on the back of a truck and they
158. 9:07became absolute
159. 9:09relativists yep but not many of them
160. 9:13took advantage of those
161. 9:15opportunities kir a Lon
162. 9:20[Music]