English subtitles for clip: File:Thirdlaw.ogv
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1 00:00:02,000 --> 00:00:03,300 Now we come 2 00:00:03,300 --> 00:00:05,700 to Newton's third law. 3 00:00:07,800 --> 00:00:09,500 “If one object 4 00:00:09,500 --> 00:00:11,700 exerts a force on another, 5 00:00:13,200 --> 00:00:15,400 the other exerts the same force 6 00:00:15,400 --> 00:00:17,700 in opposite direction on the one.“ 7 00:00:19,400 --> 00:00:20,200 I read it again: 8 00:00:20,200 --> 00:00:22,700 “If one object exerts a force 9 00:00:24,000 --> 00:00:25,000 on another, 10 00:00:26,500 --> 00:00:29,800 the other exerts the same force in opposite direction 11 00:00:29,800 --> 00:00:30,600 on the one.” 12 00:00:31,500 --> 00:00:32,300 And I 13 00:00:32,300 --> 00:00:33,150 normally 14 00:00:35,100 --> 00:00:36,300 summarize that 15 00:00:37,800 --> 00:00:38,600 as follows 16 00:00:39,000 --> 00:00:39,900 the third law 17 00:00:41,100 --> 00:00:42,000 as action 18 00:00:44,000 --> 00:00:45,700 equals minus reaction. 19 00:00:49,100 --> 00:00:51,100 And the minus sign indicates then 20 00:00:51,740 --> 00:00:52,700 that it opposes. 21 00:00:52,700 --> 00:00:54,100 So you sit on your seats 22 00:00:55,150 --> 00:00:57,400 'n' you're pulled down on your seats, 23 00:00:58,550 --> 00:00:59,650 because of gravity, 24 00:01:00,800 --> 00:01:02,700 and the seats will push back on you 25 00:01:03,400 --> 00:01:05,100 with the same force. 26 00:01:05,400 --> 00:01:07,600 Action equals minus reaction. 27 00:01:08,000 --> 00:01:09,800 I held the baseball in my hand 28 00:01:11,550 --> 00:01:13,150 the baseball pushes on my hand 29 00:01:13,150 --> 00:01:14,250 with a certain force, 30 00:01:14,500 --> 00:01:16,200 I push on the baseball 31 00:01:16,400 --> 00:01:17,500 with the same force. 32 00:01:18,800 --> 00:01:20,505 I push against the wall 33 00:01:20,905 --> 00:01:22,200 with a certain force 34 00:01:22,355 --> 00:01:23,600 the wall pushes back 35 00:01:23,805 --> 00:01:26,800 in the opposite direction with exactly the same force. 36 00:01:27,205 --> 00:01:29,350 The third law always holds. 37 00:01:29,350 --> 00:01:31,005 Whether the objects 38 00:01:31,005 --> 00:01:33,400 are moving or accelerated 39 00:01:33,400 --> 00:01:34,500 makes no difference. 40 00:01:34,805 --> 00:01:36,900 All moments in time 41 00:01:37,155 --> 00:01:40,200 the force – we call it actually the contact force – 42 00:01:40,200 --> 00:01:41,700 between two objects 43 00:01:42,100 --> 00:01:45,100 one on the other is always the same as the other on one 44 00:01:45,100 --> 00:01:48,255 but in the opposite direction.