1 00:00:00,740 --> 00:00:03,320 the show you're about to watch concerns 2 00:00:03,320 --> 00:00:03,330 the show you're about to watch concerns 3 00:00:03,330 --> 00:00:05,090 the show you're about to watch concerns the space shuttle mission unlike any 4 00:00:05,090 --> 00:00:05,100 the space shuttle mission unlike any 5 00:00:05,100 --> 00:00:06,950 the space shuttle mission unlike any other you've ever seen the tethered 6 00:00:06,950 --> 00:00:06,960 other you've ever seen the tethered 7 00:00:06,960 --> 00:00:09,200 other you've ever seen the tethered satellite mission while the mission was 8 00:00:09,200 --> 00:00:09,210 satellite mission while the mission was 9 00:00:09,210 --> 00:00:11,299 satellite mission while the mission was successful in proving an idea that had 10 00:00:11,299 --> 00:00:11,309 successful in proving an idea that had 11 00:00:11,309 --> 00:00:13,580 successful in proving an idea that had only been a theory we had some hardware 12 00:00:13,580 --> 00:00:13,590 only been a theory we had some hardware 13 00:00:13,590 --> 00:00:15,410 only been a theory we had some hardware problems and the tether did not extend 14 00:00:15,410 --> 00:00:15,420 problems and the tether did not extend 15 00:00:15,420 --> 00:00:18,529 problems and the tether did not extend as far as we wanted it to go as often 16 00:00:18,529 --> 00:00:18,539 as far as we wanted it to go as often 17 00:00:18,539 --> 00:00:20,540 as far as we wanted it to go as often happens in research we learn from things 18 00:00:20,540 --> 00:00:20,550 happens in research we learn from things 19 00:00:20,550 --> 00:00:22,730 happens in research we learn from things when they go wrong here we learned 20 00:00:22,730 --> 00:00:22,740 when they go wrong here we learned 21 00:00:22,740 --> 00:00:24,200 when they go wrong here we learned enough to prove that this truly unique 22 00:00:24,200 --> 00:00:24,210 enough to prove that this truly unique 23 00:00:24,210 --> 00:00:26,029 enough to prove that this truly unique concept really does work 24 00:00:26,029 --> 00:00:26,039 concept really does work 25 00:00:26,039 --> 00:00:29,179 concept really does work in this program we do calculations based 26 00:00:29,179 --> 00:00:29,189 in this program we do calculations based 27 00:00:29,189 --> 00:00:31,370 in this program we do calculations based on the length we expected the tether to 28 00:00:31,370 --> 00:00:31,380 on the length we expected the tether to 29 00:00:31,380 --> 00:00:34,160 on the length we expected the tether to extend not how far it actually extended 30 00:00:34,160 --> 00:00:34,170 extend not how far it actually extended 31 00:00:34,170 --> 00:00:40,000 extend not how far it actually extended so keep this in mind and enjoy the show 32 00:00:40,000 --> 00:00:40,010 33 00:00:40,010 --> 00:01:41,830 - 34 00:01:41,830 --> 00:01:41,840 35 00:01:41,840 --> 00:01:44,990 an ordinary summer's day at the lake the 36 00:01:44,990 --> 00:01:45,000 an ordinary summer's day at the lake the 37 00:01:45,000 --> 00:01:49,630 an ordinary summer's day at the lake the Sun the water good fun and physics 38 00:01:49,630 --> 00:01:49,640 Sun the water good fun and physics 39 00:01:49,640 --> 00:01:53,650 Sun the water good fun and physics physics you might not think so but yes 40 00:01:53,650 --> 00:01:53,660 physics you might not think so but yes 41 00:01:53,660 --> 00:01:56,290 physics you might not think so but yes take this water skier for example 42 00:01:56,290 --> 00:01:56,300 take this water skier for example 43 00:01:56,300 --> 00:01:58,970 take this water skier for example there's a lot of basic physics involved 44 00:01:58,970 --> 00:01:58,980 there's a lot of basic physics involved 45 00:01:58,980 --> 00:02:02,030 there's a lot of basic physics involved in skiing there's the force of gravity 46 00:02:02,030 --> 00:02:02,040 in skiing there's the force of gravity 47 00:02:02,040 --> 00:02:05,150 in skiing there's the force of gravity the pull of the rope the resistance of 48 00:02:05,150 --> 00:02:05,160 the pull of the rope the resistance of 49 00:02:05,160 --> 00:02:07,970 the pull of the rope the resistance of the water the skier balances these 50 00:02:07,970 --> 00:02:07,980 the water the skier balances these 51 00:02:07,980 --> 00:02:10,580 the water the skier balances these forces and a few more to keep a stable 52 00:02:10,580 --> 00:02:10,590 forces and a few more to keep a stable 53 00:02:10,590 --> 00:02:13,210 forces and a few more to keep a stable center of mass gliding across the water 54 00:02:13,210 --> 00:02:13,220 center of mass gliding across the water 55 00:02:13,220 --> 00:02:16,699 center of mass gliding across the water but the physics is so basic he doesn't 56 00:02:16,699 --> 00:02:16,709 but the physics is so basic he doesn't 57 00:02:16,709 --> 00:02:18,199 but the physics is so basic he doesn't even have to think about it 58 00:02:18,199 --> 00:02:18,209 even have to think about it 59 00:02:18,209 --> 00:02:21,680 even have to think about it he just skis and if he doesn't get it 60 00:02:21,680 --> 00:02:21,690 he just skis and if he doesn't get it 61 00:02:21,690 --> 00:02:23,660 he just skis and if he doesn't get it right the first time he tries again 62 00:02:23,660 --> 00:02:23,670 right the first time he tries again 63 00:02:23,670 --> 00:02:27,170 right the first time he tries again until he does but in space 64 00:02:27,170 --> 00:02:27,180 until he does but in space 65 00:02:27,180 --> 00:02:31,210 until he does but in space we usually get only one shot at a task 66 00:02:31,210 --> 00:02:31,220 we usually get only one shot at a task 67 00:02:31,220 --> 00:02:35,210 we usually get only one shot at a task so before we do anything we analyze it 68 00:02:35,210 --> 00:02:35,220 so before we do anything we analyze it 69 00:02:35,220 --> 00:02:38,050 so before we do anything we analyze it to get the physics right the first time 70 00:02:38,050 --> 00:02:38,060 to get the physics right the first time 71 00:02:38,060 --> 00:02:41,180 to get the physics right the first time that's important because what you think 72 00:02:41,180 --> 00:02:41,190 that's important because what you think 73 00:02:41,190 --> 00:02:43,670 that's important because what you think should happen in space isn't necessarily 74 00:02:43,670 --> 00:02:43,680 should happen in space isn't necessarily 75 00:02:43,680 --> 00:02:46,820 should happen in space isn't necessarily what will happen let's say we want to 76 00:02:46,820 --> 00:02:46,830 what will happen let's say we want to 77 00:02:46,830 --> 00:02:49,190 what will happen let's say we want to speed up the orbiter to rendezvous with 78 00:02:49,190 --> 00:02:49,200 speed up the orbiter to rendezvous with 79 00:02:49,200 --> 00:02:52,699 speed up the orbiter to rendezvous with a spacecraft just ahead do we fire the 80 00:02:52,699 --> 00:02:52,709 a spacecraft just ahead do we fire the 81 00:02:52,709 --> 00:02:56,930 a spacecraft just ahead do we fire the orbiters jets to go faster no if we 82 00:02:56,930 --> 00:02:56,940 orbiters jets to go faster no if we 83 00:02:56,940 --> 00:02:59,240 orbiters jets to go faster no if we follow intuition and fire the jets to 84 00:02:59,240 --> 00:02:59,250 follow intuition and fire the jets to 85 00:02:59,250 --> 00:03:02,240 follow intuition and fire the jets to speed up will actually be propelled into 86 00:03:02,240 --> 00:03:02,250 speed up will actually be propelled into 87 00:03:02,250 --> 00:03:04,790 speed up will actually be propelled into a higher orbit that will end up slowing 88 00:03:04,790 --> 00:03:04,800 a higher orbit that will end up slowing 89 00:03:04,800 --> 00:03:08,570 a higher orbit that will end up slowing us down so up here in space we can't 90 00:03:08,570 --> 00:03:08,580 us down so up here in space we can't 91 00:03:08,580 --> 00:03:10,310 us down so up here in space we can't always depend on what we think will 92 00:03:10,310 --> 00:03:10,320 always depend on what we think will 93 00:03:10,320 --> 00:03:12,710 always depend on what we think will happen we have to know what will happen 94 00:03:12,710 --> 00:03:12,720 happen we have to know what will happen 95 00:03:12,720 --> 00:03:15,140 happen we have to know what will happen and that takes a good understanding of 96 00:03:15,140 --> 00:03:15,150 and that takes a good understanding of 97 00:03:15,150 --> 00:03:24,300 and that takes a good understanding of physics 98 00:03:24,300 --> 00:03:24,310 99 00:03:24,310 --> 00:03:27,000 physics whether we use it to rendezvous 100 00:03:27,000 --> 00:03:27,010 physics whether we use it to rendezvous 101 00:03:27,010 --> 00:03:29,010 physics whether we use it to rendezvous with satellites in space or describe 102 00:03:29,010 --> 00:03:29,020 with satellites in space or describe 103 00:03:29,020 --> 00:03:31,339 with satellites in space or describe waterskiing on the earth has unlimited 104 00:03:31,339 --> 00:03:31,349 waterskiing on the earth has unlimited 105 00:03:31,349 --> 00:03:34,020 waterskiing on the earth has unlimited applications and today we have a really 106 00:03:34,020 --> 00:03:34,030 applications and today we have a really 107 00:03:34,030 --> 00:03:39,479 applications and today we have a really unique one to show you welcome aboard 108 00:03:39,479 --> 00:03:39,489 unique one to show you welcome aboard 109 00:03:39,489 --> 00:03:41,699 unique one to show you welcome aboard the space shuttle Atlantis where we're 110 00:03:41,699 --> 00:03:41,709 the space shuttle Atlantis where we're 111 00:03:41,709 --> 00:03:43,520 the space shuttle Atlantis where we're about to launch a new type of spacecraft 112 00:03:43,520 --> 00:03:43,530 about to launch a new type of spacecraft 113 00:03:43,530 --> 00:03:46,080 about to launch a new type of spacecraft it's called the tethered satellite 114 00:03:46,080 --> 00:03:46,090 it's called the tethered satellite 115 00:03:46,090 --> 00:03:48,780 it's called the tethered satellite that's because the entire time it's 116 00:03:48,780 --> 00:03:48,790 that's because the entire time it's 117 00:03:48,790 --> 00:03:51,509 that's because the entire time it's deployed it remains tethered to the 118 00:03:51,509 --> 00:03:51,519 deployed it remains tethered to the 119 00:03:51,519 --> 00:03:53,580 deployed it remains tethered to the orbiter by a two millimeter diameter 120 00:03:53,580 --> 00:03:53,590 orbiter by a two millimeter diameter 121 00:03:53,590 --> 00:03:57,990 orbiter by a two millimeter diameter strand of insulated copper this is one 122 00:03:57,990 --> 00:03:58,000 strand of insulated copper this is one 123 00:03:58,000 --> 00:03:59,940 strand of insulated copper this is one of the most complex missions ever 124 00:03:59,940 --> 00:03:59,950 of the most complex missions ever 125 00:03:59,950 --> 00:04:03,960 of the most complex missions ever attempted by a space shuttle crew what's 126 00:04:03,960 --> 00:04:03,970 attempted by a space shuttle crew what's 127 00:04:03,970 --> 00:04:06,180 attempted by a space shuttle crew what's amazing is that most of the physics that 128 00:04:06,180 --> 00:04:06,190 amazing is that most of the physics that 129 00:04:06,190 --> 00:04:08,309 amazing is that most of the physics that we use to fly the tethered satellite is 130 00:04:08,309 --> 00:04:08,319 we use to fly the tethered satellite is 131 00:04:08,319 --> 00:04:10,530 we use to fly the tethered satellite is the same physics that you study in high 132 00:04:10,530 --> 00:04:10,540 the same physics that you study in high 133 00:04:10,540 --> 00:04:13,500 the same physics that you study in high school it includes concepts like gravity 134 00:04:13,500 --> 00:04:13,510 school it includes concepts like gravity 135 00:04:13,510 --> 00:04:17,069 school it includes concepts like gravity angular momentum and center of mass in 136 00:04:17,069 --> 00:04:17,079 angular momentum and center of mass in 137 00:04:17,079 --> 00:04:19,890 angular momentum and center of mass in the next few minutes we're going to see 138 00:04:19,890 --> 00:04:19,900 the next few minutes we're going to see 139 00:04:19,900 --> 00:04:22,500 the next few minutes we're going to see how these concepts relate to the orbiter 140 00:04:22,500 --> 00:04:22,510 how these concepts relate to the orbiter 141 00:04:22,510 --> 00:04:27,270 how these concepts relate to the orbiter the satellite and the tether we begin 142 00:04:27,270 --> 00:04:27,280 the satellite and the tether we begin 143 00:04:27,280 --> 00:04:29,820 the satellite and the tether we begin the experiment by deploying the tethered 144 00:04:29,820 --> 00:04:29,830 the experiment by deploying the tethered 145 00:04:29,830 --> 00:04:33,360 the experiment by deploying the tethered satellite we do this from the top of a 146 00:04:33,360 --> 00:04:33,370 satellite we do this from the top of a 147 00:04:33,370 --> 00:04:36,240 satellite we do this from the top of a 12 metre boom to protect sensitive parts 148 00:04:36,240 --> 00:04:36,250 12 metre boom to protect sensitive parts 149 00:04:36,250 --> 00:04:40,440 12 metre boom to protect sensitive parts of the orbiter small invisible nitrogen 150 00:04:40,440 --> 00:04:40,450 of the orbiter small invisible nitrogen 151 00:04:40,450 --> 00:04:42,960 of the orbiter small invisible nitrogen jets are used to get the satellite and 152 00:04:42,960 --> 00:04:42,970 jets are used to get the satellite and 153 00:04:42,970 --> 00:04:45,690 jets are used to get the satellite and tether in motion once they are far 154 00:04:45,690 --> 00:04:45,700 tether in motion once they are far 155 00:04:45,700 --> 00:04:47,760 tether in motion once they are far enough away from the orbiter we can turn 156 00:04:47,760 --> 00:04:47,770 enough away from the orbiter we can turn 157 00:04:47,770 --> 00:04:49,830 enough away from the orbiter we can turn the Jets off and the satellite and 158 00:04:49,830 --> 00:04:49,840 the Jets off and the satellite and 159 00:04:49,840 --> 00:04:52,430 the Jets off and the satellite and tether will continue to deploy 160 00:04:52,430 --> 00:04:52,440 tether will continue to deploy 161 00:04:52,440 --> 00:04:54,800 tether will continue to deploy what makes the satellites continue to go 162 00:04:54,800 --> 00:04:54,810 what makes the satellites continue to go 163 00:04:54,810 --> 00:04:58,030 what makes the satellites continue to go up after all you can't push on the road 164 00:04:58,030 --> 00:04:58,040 up after all you can't push on the road 165 00:04:58,040 --> 00:05:00,470 up after all you can't push on the road well that's where the physics comes in 166 00:05:00,470 --> 00:05:00,480 well that's where the physics comes in 167 00:05:00,480 --> 00:05:03,260 well that's where the physics comes in we take advantage of a force that causes 168 00:05:03,260 --> 00:05:03,270 we take advantage of a force that causes 169 00:05:03,270 --> 00:05:05,210 we take advantage of a force that causes the tether to continue extending on its 170 00:05:05,210 --> 00:05:05,220 the tether to continue extending on its 171 00:05:05,220 --> 00:05:08,360 the tether to continue extending on its own away from the earth it's a force 172 00:05:08,360 --> 00:05:08,370 own away from the earth it's a force 173 00:05:08,370 --> 00:05:10,760 own away from the earth it's a force that gets stronger as the tether gets 174 00:05:10,760 --> 00:05:10,770 that gets stronger as the tether gets 175 00:05:10,770 --> 00:05:14,960 that gets stronger as the tether gets longer when what is this force well its 176 00:05:14,960 --> 00:05:14,970 longer when what is this force well its 177 00:05:14,970 --> 00:05:19,160 longer when what is this force well its gravity gravity but how can gravity make 178 00:05:19,160 --> 00:05:19,170 gravity gravity but how can gravity make 179 00:05:19,170 --> 00:05:22,580 gravity gravity but how can gravity make things go up well which one of those 180 00:05:22,580 --> 00:05:22,590 things go up well which one of those 181 00:05:22,590 --> 00:05:24,020 things go up well which one of those things that doesn't make sense that's in 182 00:05:24,020 --> 00:05:24,030 things that doesn't make sense that's in 183 00:05:24,030 --> 00:05:26,360 things that doesn't make sense that's in you understand the physics so let's look 184 00:05:26,360 --> 00:05:26,370 you understand the physics so let's look 185 00:05:26,370 --> 00:05:30,380 you understand the physics so let's look at the physics of gravity all objects 186 00:05:30,380 --> 00:05:30,390 at the physics of gravity all objects 187 00:05:30,390 --> 00:05:32,510 at the physics of gravity all objects are cooled by Earth's gravity even 188 00:05:32,510 --> 00:05:32,520 are cooled by Earth's gravity even 189 00:05:32,520 --> 00:05:36,470 are cooled by Earth's gravity even objects in space but the further away 190 00:05:36,470 --> 00:05:36,480 objects in space but the further away 191 00:05:36,480 --> 00:05:38,840 objects in space but the further away from the earthly objects are the less 192 00:05:38,840 --> 00:05:38,850 from the earthly objects are the less 193 00:05:38,850 --> 00:05:42,410 from the earthly objects are the less the earth gravity pulls on them Sir 194 00:05:42,410 --> 00:05:42,420 the earth gravity pulls on them Sir 195 00:05:42,420 --> 00:05:44,510 the earth gravity pulls on them Sir Isaac Newton described the force due to 196 00:05:44,510 --> 00:05:44,520 Isaac Newton described the force due to 197 00:05:44,520 --> 00:05:47,810 Isaac Newton described the force due to gravity as an inverse square law that 198 00:05:47,810 --> 00:05:47,820 gravity as an inverse square law that 199 00:05:47,820 --> 00:05:50,000 gravity as an inverse square law that means that an object two times as far 200 00:05:50,000 --> 00:05:50,010 means that an object two times as far 201 00:05:50,010 --> 00:05:51,770 means that an object two times as far away from the center of the earth at 202 00:05:51,770 --> 00:05:51,780 away from the center of the earth at 203 00:05:51,780 --> 00:05:54,290 away from the center of the earth at another object with the same mass fields 204 00:05:54,290 --> 00:05:54,300 another object with the same mass fields 205 00:05:54,300 --> 00:05:56,440 another object with the same mass fields only a quarter of the gravitational pull 206 00:05:56,440 --> 00:05:56,450 only a quarter of the gravitational pull 207 00:05:56,450 --> 00:05:59,300 only a quarter of the gravitational pull it's a mouthful but next to the tether 208 00:05:59,300 --> 00:05:59,310 it's a mouthful but next to the tether 209 00:05:59,310 --> 00:06:01,940 it's a mouthful but next to the tether gravity is the most important influence 210 00:06:01,940 --> 00:06:01,950 gravity is the most important influence 211 00:06:01,950 --> 00:06:06,620 gravity is the most important influence on our tethered satellite let's find out 212 00:06:06,620 --> 00:06:06,630 on our tethered satellite let's find out 213 00:06:06,630 --> 00:06:09,860 on our tethered satellite let's find out why we'll calculate using Newton's to 214 00:06:09,860 --> 00:06:09,870 why we'll calculate using Newton's to 215 00:06:09,870 --> 00:06:11,370 why we'll calculate using Newton's to measure the 216 00:06:11,370 --> 00:06:11,380 measure the 217 00:06:11,380 --> 00:06:14,620 measure the when the 500 kilogram satellite is in 218 00:06:14,620 --> 00:06:14,630 when the 500 kilogram satellite is in 219 00:06:14,630 --> 00:06:16,779 when the 500 kilogram satellite is in the cargo bay six thousand seven hundred 220 00:06:16,779 --> 00:06:16,789 the cargo bay six thousand seven hundred 221 00:06:16,789 --> 00:06:18,520 the cargo bay six thousand seven hundred kilometers from the center of the earth 222 00:06:18,520 --> 00:06:18,530 kilometers from the center of the earth 223 00:06:18,530 --> 00:06:21,960 kilometers from the center of the earth it has a certain amount of force on it 224 00:06:21,960 --> 00:06:21,970 it has a certain amount of force on it 225 00:06:21,970 --> 00:06:25,469 it has a certain amount of force on it if we extend its 10 kilometers upwards 226 00:06:25,469 --> 00:06:25,479 if we extend its 10 kilometers upwards 227 00:06:25,479 --> 00:06:28,480 if we extend its 10 kilometers upwards gravity pulls on it about 30 Newtons 228 00:06:28,480 --> 00:06:28,490 gravity pulls on it about 30 Newtons 229 00:06:28,490 --> 00:06:31,330 gravity pulls on it about 30 Newtons less extending it's another ten 230 00:06:31,330 --> 00:06:31,340 less extending it's another ten 231 00:06:31,340 --> 00:06:33,640 less extending it's another ten kilometers reduces gravity is gripped by 232 00:06:33,640 --> 00:06:33,650 kilometers reduces gravity is gripped by 233 00:06:33,650 --> 00:06:35,170 kilometers reduces gravity is gripped by another 13 Newtons 234 00:06:35,170 --> 00:06:35,180 another 13 Newtons 235 00:06:35,180 --> 00:06:40,330 another 13 Newtons for a total of 26 we said that gravity 236 00:06:40,330 --> 00:06:40,340 for a total of 26 we said that gravity 237 00:06:40,340 --> 00:06:43,900 for a total of 26 we said that gravity is an inverse-square force and for our 238 00:06:43,900 --> 00:06:43,910 is an inverse-square force and for our 239 00:06:43,910 --> 00:06:46,749 is an inverse-square force and for our purposes the distance involved is from 240 00:06:46,749 --> 00:06:46,759 purposes the distance involved is from 241 00:06:46,759 --> 00:06:50,230 purposes the distance involved is from the center of the Earth's orbit and to 242 00:06:50,230 --> 00:06:50,240 the center of the Earth's orbit and to 243 00:06:50,240 --> 00:06:52,089 the center of the Earth's orbit and to the satellite as it moved away from the 244 00:06:52,089 --> 00:06:52,099 the satellite as it moved away from the 245 00:06:52,099 --> 00:06:55,600 the satellite as it moved away from the orbital but the distances the satellite 246 00:06:55,600 --> 00:06:55,610 orbital but the distances the satellite 247 00:06:55,610 --> 00:06:57,310 orbital but the distances the satellite is moving away from the orbiter are much 248 00:06:57,310 --> 00:06:57,320 is moving away from the orbiter are much 249 00:06:57,320 --> 00:06:59,140 is moving away from the orbiter are much smaller than the distance to the center 250 00:06:59,140 --> 00:06:59,150 smaller than the distance to the center 251 00:06:59,150 --> 00:07:02,439 smaller than the distance to the center of the earth if you put a force on these 252 00:07:02,439 --> 00:07:02,449 of the earth if you put a force on these 253 00:07:02,449 --> 00:07:05,860 of the earth if you put a force on these smaller distances we see that the change 254 00:07:05,860 --> 00:07:05,870 smaller distances we see that the change 255 00:07:05,870 --> 00:07:08,589 smaller distances we see that the change in force is linearly proportional to the 256 00:07:08,589 --> 00:07:08,599 in force is linearly proportional to the 257 00:07:08,599 --> 00:07:11,140 in force is linearly proportional to the change in distance 258 00:07:11,140 --> 00:07:11,150 change in distance 259 00:07:11,150 --> 00:07:13,810 change in distance we call this difference in the force of 260 00:07:13,810 --> 00:07:13,820 we call this difference in the force of 261 00:07:13,820 --> 00:07:16,450 we call this difference in the force of gravity with distance the gravity 262 00:07:16,450 --> 00:07:16,460 gravity with distance the gravity 263 00:07:16,460 --> 00:07:19,300 gravity with distance the gravity gradient force Britons being the 264 00:07:19,300 --> 00:07:19,310 gradient force Britons being the 265 00:07:19,310 --> 00:07:22,330 gradient force Britons being the mathematical term for difference 266 00:07:22,330 --> 00:07:22,340 mathematical term for difference 267 00:07:22,340 --> 00:07:25,120 mathematical term for difference when the tether length doubles the 268 00:07:25,120 --> 00:07:25,130 when the tether length doubles the 269 00:07:25,130 --> 00:07:28,990 when the tether length doubles the gravity gradient force doubles 270 00:07:28,990 --> 00:07:29,000 271 00:07:29,000 --> 00:07:31,129 now we have enough information to 272 00:07:31,129 --> 00:07:31,139 now we have enough information to 273 00:07:31,139 --> 00:07:33,320 now we have enough information to understand why the tether reels out and 274 00:07:33,320 --> 00:07:33,330 understand why the tether reels out and 275 00:07:33,330 --> 00:07:36,640 understand why the tether reels out and stays out so let's put it all together 276 00:07:36,640 --> 00:07:36,650 stays out so let's put it all together 277 00:07:36,650 --> 00:07:39,230 stays out so let's put it all together the acceleration caused by the Earth's 278 00:07:39,230 --> 00:07:39,240 the acceleration caused by the Earth's 279 00:07:39,240 --> 00:07:41,959 the acceleration caused by the Earth's gravity is greater for objects closer to 280 00:07:41,959 --> 00:07:41,969 gravity is greater for objects closer to 281 00:07:41,969 --> 00:07:42,890 gravity is greater for objects closer to the Earth's center 282 00:07:42,890 --> 00:07:42,900 the Earth's center 283 00:07:42,900 --> 00:07:45,050 the Earth's center this means the orbiter is trying to 284 00:07:45,050 --> 00:07:45,060 this means the orbiter is trying to 285 00:07:45,060 --> 00:07:47,240 this means the orbiter is trying to accelerate towards the Earth faster than 286 00:07:47,240 --> 00:07:47,250 accelerate towards the Earth faster than 287 00:07:47,250 --> 00:07:49,309 accelerate towards the Earth faster than the satellite this extra acceleration 288 00:07:49,309 --> 00:07:49,319 the satellite this extra acceleration 289 00:07:49,319 --> 00:07:52,189 the satellite this extra acceleration causes the orbiter to want to fall away 290 00:07:52,189 --> 00:07:52,199 causes the orbiter to want to fall away 291 00:07:52,199 --> 00:07:55,040 causes the orbiter to want to fall away from the satellite creating a stretching 292 00:07:55,040 --> 00:07:55,050 from the satellite creating a stretching 293 00:07:55,050 --> 00:07:56,890 from the satellite creating a stretching force along the length of the tether and 294 00:07:56,890 --> 00:07:56,900 force along the length of the tether and 295 00:07:56,900 --> 00:07:59,179 force along the length of the tether and that's the force that keeps the tether 296 00:07:59,179 --> 00:07:59,189 that's the force that keeps the tether 297 00:07:59,189 --> 00:08:01,610 that's the force that keeps the tether taut and makes the tethered satellite go 298 00:08:01,610 --> 00:08:01,620 taut and makes the tethered satellite go 299 00:08:01,620 --> 00:08:04,580 taut and makes the tethered satellite go up but how can gravity make something go 300 00:08:04,580 --> 00:08:04,590 up but how can gravity make something go 301 00:08:04,590 --> 00:08:06,439 up but how can gravity make something go up doesn't that violate the law of 302 00:08:06,439 --> 00:08:06,449 up doesn't that violate the law of 303 00:08:06,449 --> 00:08:07,809 up doesn't that violate the law of conservation of energy 304 00:08:07,809 --> 00:08:07,819 conservation of energy 305 00:08:07,819 --> 00:08:10,010 conservation of energy could we be getting something for 306 00:08:10,010 --> 00:08:10,020 could we be getting something for 307 00:08:10,020 --> 00:08:13,249 could we be getting something for nothing to understand how gravity can 308 00:08:13,249 --> 00:08:13,259 nothing to understand how gravity can 309 00:08:13,259 --> 00:08:15,080 nothing to understand how gravity can make something go up we need to go a 310 00:08:15,080 --> 00:08:15,090 make something go up we need to go a 311 00:08:15,090 --> 00:08:17,240 make something go up we need to go a little deeper into dynamics and look at 312 00:08:17,240 --> 00:08:17,250 little deeper into dynamics and look at 313 00:08:17,250 --> 00:08:21,019 little deeper into dynamics and look at the concept of center of mass the center 314 00:08:21,019 --> 00:08:21,029 the concept of center of mass the center 315 00:08:21,029 --> 00:08:23,480 the concept of center of mass the center of mass is the point in a system where 316 00:08:23,480 --> 00:08:23,490 of mass is the point in a system where 317 00:08:23,490 --> 00:08:25,640 of mass is the point in a system where the system is evenly distributed and in 318 00:08:25,640 --> 00:08:25,650 the system is evenly distributed and in 319 00:08:25,650 --> 00:08:28,519 the system is evenly distributed and in balance balance or equilibrium is 320 00:08:28,519 --> 00:08:28,529 balance balance or equilibrium is 321 00:08:28,529 --> 00:08:30,890 balance balance or equilibrium is important because it means the system is 322 00:08:30,890 --> 00:08:30,900 important because it means the system is 323 00:08:30,900 --> 00:08:33,680 important because it means the system is stable we're all in the same orbit 324 00:08:33,680 --> 00:08:33,690 stable we're all in the same orbit 325 00:08:33,690 --> 00:08:36,560 stable we're all in the same orbit around the Earth Jeff the orbiter and 326 00:08:36,560 --> 00:08:36,570 around the Earth Jeff the orbiter and 327 00:08:36,570 --> 00:08:39,620 around the Earth Jeff the orbiter and these two apples the center of mass 328 00:08:39,620 --> 00:08:39,630 these two apples the center of mass 329 00:08:39,630 --> 00:08:42,319 these two apples the center of mass between two objects such as these apples 330 00:08:42,319 --> 00:08:42,329 between two objects such as these apples 331 00:08:42,329 --> 00:08:44,209 between two objects such as these apples doesn't change just because they're in 332 00:08:44,209 --> 00:08:44,219 doesn't change just because they're in 333 00:08:44,219 --> 00:08:47,000 doesn't change just because they're in orbit their center of mass is between 334 00:08:47,000 --> 00:08:47,010 orbit their center of mass is between 335 00:08:47,010 --> 00:08:49,790 orbit their center of mass is between them here when I start them spinning 336 00:08:49,790 --> 00:08:49,800 them here when I start them spinning 337 00:08:49,800 --> 00:08:52,250 them here when I start them spinning their center of mass continues to be in 338 00:08:52,250 --> 00:08:52,260 their center of mass continues to be in 339 00:08:52,260 --> 00:08:55,220 their center of mass continues to be in the same place if I cut the string so 340 00:08:55,220 --> 00:08:55,230 the same place if I cut the string so 341 00:08:55,230 --> 00:08:57,110 the same place if I cut the string so the apples are attached by the longer 342 00:08:57,110 --> 00:08:57,120 the apples are attached by the longer 343 00:08:57,120 --> 00:08:59,930 the apples are attached by the longer string the center of mass is still in 344 00:08:59,930 --> 00:08:59,940 string the center of mass is still in 345 00:08:59,940 --> 00:09:02,389 string the center of mass is still in the same place inside the orbiter which 346 00:09:02,389 --> 00:09:02,399 the same place inside the orbiter which 347 00:09:02,399 --> 00:09:05,269 the same place inside the orbiter which means in the same orbit what does this 348 00:09:05,269 --> 00:09:05,279 means in the same orbit what does this 349 00:09:05,279 --> 00:09:07,310 means in the same orbit what does this have to do with the orbiter and tethered 350 00:09:07,310 --> 00:09:07,320 have to do with the orbiter and tethered 351 00:09:07,320 --> 00:09:10,220 have to do with the orbiter and tethered satellite when the tethered satellite is 352 00:09:10,220 --> 00:09:10,230 satellite when the tethered satellite is 353 00:09:10,230 --> 00:09:12,500 satellite when the tethered satellite is in the orbiters cargo bay the center of 354 00:09:12,500 --> 00:09:12,510 in the orbiters cargo bay the center of 355 00:09:12,510 --> 00:09:15,650 in the orbiters cargo bay the center of mass is inside the orbiter when we 356 00:09:15,650 --> 00:09:15,660 mass is inside the orbiter when we 357 00:09:15,660 --> 00:09:17,630 mass is inside the orbiter when we deploy the satellite do you think the 358 00:09:17,630 --> 00:09:17,640 deploy the satellite do you think the 359 00:09:17,640 --> 00:09:19,750 deploy the satellite do you think the orbit of the center of mass changes if 360 00:09:19,750 --> 00:09:19,760 orbit of the center of mass changes if 361 00:09:19,760 --> 00:09:23,090 orbit of the center of mass changes if it did then we would be violating the 362 00:09:23,090 --> 00:09:23,100 it did then we would be violating the 363 00:09:23,100 --> 00:09:25,600 it did then we would be violating the law of the conservation of energy 364 00:09:25,600 --> 00:09:25,610 law of the conservation of energy 365 00:09:25,610 --> 00:09:29,449 law of the conservation of energy however like the apples the orbit of the 366 00:09:29,449 --> 00:09:29,459 however like the apples the orbit of the 367 00:09:29,459 --> 00:09:31,519 however like the apples the orbit of the shuttle satellite system doesn't change 368 00:09:31,519 --> 00:09:31,529 shuttle satellite system doesn't change 369 00:09:31,529 --> 00:09:33,680 shuttle satellite system doesn't change because no external force has been 370 00:09:33,680 --> 00:09:33,690 because no external force has been 371 00:09:33,690 --> 00:09:36,410 because no external force has been applied to the system but the positions 372 00:09:36,410 --> 00:09:36,420 applied to the system but the positions 373 00:09:36,420 --> 00:09:38,510 applied to the system but the positions of the orbiter and satellite do change 374 00:09:38,510 --> 00:09:38,520 of the orbiter and satellite do change 375 00:09:38,520 --> 00:09:39,410 of the orbiter and satellite do change to keep this 376 00:09:39,410 --> 00:09:39,420 to keep this 377 00:09:39,420 --> 00:09:41,660 to keep this systems center of mass in the same orbit 378 00:09:41,660 --> 00:09:41,670 systems center of mass in the same orbit 379 00:09:41,670 --> 00:09:43,730 systems center of mass in the same orbit and continue its stable equilibrium 380 00:09:43,730 --> 00:09:43,740 and continue its stable equilibrium 381 00:09:43,740 --> 00:09:46,910 and continue its stable equilibrium around the earth let's look at that 382 00:09:46,910 --> 00:09:46,920 around the earth let's look at that 383 00:09:46,920 --> 00:09:52,310 around the earth let's look at that concept in action on the ground to make 384 00:09:52,310 --> 00:09:52,320 concept in action on the ground to make 385 00:09:52,320 --> 00:09:55,130 concept in action on the ground to make a seesaw balance one person sits in the 386 00:09:55,130 --> 00:09:55,140 a seesaw balance one person sits in the 387 00:09:55,140 --> 00:09:59,570 a seesaw balance one person sits in the middle if we add another person the one 388 00:09:59,570 --> 00:09:59,580 middle if we add another person the one 389 00:09:59,580 --> 00:10:01,610 middle if we add another person the one in the middle has to move to keep the 390 00:10:01,610 --> 00:10:01,620 in the middle has to move to keep the 391 00:10:01,620 --> 00:10:09,110 in the middle has to move to keep the center of mass in place 392 00:10:09,110 --> 00:10:09,120 393 00:10:09,120 --> 00:10:11,610 it's the same for our tethered system 394 00:10:11,610 --> 00:10:11,620 it's the same for our tethered system 395 00:10:11,620 --> 00:10:15,480 it's the same for our tethered system when the satellite is extended like the 396 00:10:15,480 --> 00:10:15,490 when the satellite is extended like the 397 00:10:15,490 --> 00:10:17,699 when the satellite is extended like the heavier person on the seesaw the orbiter 398 00:10:17,699 --> 00:10:17,709 heavier person on the seesaw the orbiter 399 00:10:17,709 --> 00:10:21,480 heavier person on the seesaw the orbiter stays closer to the center of mass let's 400 00:10:21,480 --> 00:10:21,490 stays closer to the center of mass let's 401 00:10:21,490 --> 00:10:23,370 stays closer to the center of mass let's see how much the one hundred thousand 402 00:10:23,370 --> 00:10:23,380 see how much the one hundred thousand 403 00:10:23,380 --> 00:10:25,590 see how much the one hundred thousand kilogram orbiter moves away from the 404 00:10:25,590 --> 00:10:25,600 kilogram orbiter moves away from the 405 00:10:25,600 --> 00:10:27,749 kilogram orbiter moves away from the center of mass when the five hundred 406 00:10:27,749 --> 00:10:27,759 center of mass when the five hundred 407 00:10:27,759 --> 00:10:29,939 center of mass when the five hundred kilogram satellite is deployed 20 408 00:10:29,939 --> 00:10:29,949 kilogram satellite is deployed 20 409 00:10:29,949 --> 00:10:32,850 kilogram satellite is deployed 20 kilometers you could work this problem 410 00:10:32,850 --> 00:10:32,860 kilometers you could work this problem 411 00:10:32,860 --> 00:10:36,059 kilometers you could work this problem out for yourselves because the orbiter 412 00:10:36,059 --> 00:10:36,069 out for yourselves because the orbiter 413 00:10:36,069 --> 00:10:38,670 out for yourselves because the orbiter is more massive it moves only about a 414 00:10:38,670 --> 00:10:38,680 is more massive it moves only about a 415 00:10:38,680 --> 00:10:40,470 is more massive it moves only about a hundred meters away from the center of 416 00:10:40,470 --> 00:10:40,480 hundred meters away from the center of 417 00:10:40,480 --> 00:10:43,490 hundred meters away from the center of mass while the satellite moves away 418 00:10:43,490 --> 00:10:43,500 mass while the satellite moves away 419 00:10:43,500 --> 00:10:47,129 mass while the satellite moves away almost 20 kilometers and the center of 420 00:10:47,129 --> 00:10:47,139 almost 20 kilometers and the center of 421 00:10:47,139 --> 00:10:49,259 almost 20 kilometers and the center of mass of the system stays in its original 422 00:10:49,259 --> 00:10:49,269 mass of the system stays in its original 423 00:10:49,269 --> 00:10:52,769 mass of the system stays in its original orbit because the orbiter moves so 424 00:10:52,769 --> 00:10:52,779 orbit because the orbiter moves so 425 00:10:52,779 --> 00:10:54,660 orbit because the orbiter moves so little it almost seems like the 426 00:10:54,660 --> 00:10:54,670 little it almost seems like the 427 00:10:54,670 --> 00:10:57,720 little it almost seems like the satellite alone is moving up but now we 428 00:10:57,720 --> 00:10:57,730 satellite alone is moving up but now we 429 00:10:57,730 --> 00:11:00,749 satellite alone is moving up but now we know both objects are moving one up and 430 00:11:00,749 --> 00:11:00,759 know both objects are moving one up and 431 00:11:00,759 --> 00:11:03,870 know both objects are moving one up and one down once you understand this 432 00:11:03,870 --> 00:11:03,880 one down once you understand this 433 00:11:03,880 --> 00:11:06,180 one down once you understand this principle you can also see this 434 00:11:06,180 --> 00:11:06,190 principle you can also see this 435 00:11:06,190 --> 00:11:09,329 principle you can also see this situation is symmetrical we could just 436 00:11:09,329 --> 00:11:09,339 situation is symmetrical we could just 437 00:11:09,339 --> 00:11:11,069 situation is symmetrical we could just as easily have made the satellite go 438 00:11:11,069 --> 00:11:11,079 as easily have made the satellite go 439 00:11:11,079 --> 00:11:14,100 as easily have made the satellite go down 20 kilometers in the orbiter go up 440 00:11:14,100 --> 00:11:14,110 down 20 kilometers in the orbiter go up 441 00:11:14,110 --> 00:11:17,730 down 20 kilometers in the orbiter go up 100 meters 442 00:11:17,730 --> 00:11:17,740 443 00:11:17,740 --> 00:11:20,820 here's another way of looking at it 444 00:11:20,820 --> 00:11:20,830 here's another way of looking at it 445 00:11:20,830 --> 00:11:23,830 here's another way of looking at it think of a pulley system a heavyweight 446 00:11:23,830 --> 00:11:23,840 think of a pulley system a heavyweight 447 00:11:23,840 --> 00:11:26,170 think of a pulley system a heavyweight moves a little to balance a light weight 448 00:11:26,170 --> 00:11:26,180 moves a little to balance a light weight 449 00:11:26,180 --> 00:11:29,020 moves a little to balance a light weight that moves a lot the weights can move in 450 00:11:29,020 --> 00:11:29,030 that moves a lot the weights can move in 451 00:11:29,030 --> 00:11:31,030 that moves a lot the weights can move in either direction the center of mass 452 00:11:31,030 --> 00:11:31,040 either direction the center of mass 453 00:11:31,040 --> 00:11:34,150 either direction the center of mass stays constant but in space we don't 454 00:11:34,150 --> 00:11:34,160 stays constant but in space we don't 455 00:11:34,160 --> 00:11:37,420 stays constant but in space we don't need a pulley a tether will do now let's 456 00:11:37,420 --> 00:11:37,430 need a pulley a tether will do now let's 457 00:11:37,430 --> 00:11:39,100 need a pulley a tether will do now let's look at the forces that keep the tether 458 00:11:39,100 --> 00:11:39,110 look at the forces that keep the tether 459 00:11:39,110 --> 00:11:42,730 look at the forces that keep the tether system stable along a vertical axis when 460 00:11:42,730 --> 00:11:42,740 system stable along a vertical axis when 461 00:11:42,740 --> 00:11:44,950 system stable along a vertical axis when this toy is punched gravity makes it 462 00:11:44,950 --> 00:11:44,960 this toy is punched gravity makes it 463 00:11:44,960 --> 00:11:47,920 this toy is punched gravity makes it return to a vertical position the 464 00:11:47,920 --> 00:11:47,930 return to a vertical position the 465 00:11:47,930 --> 00:11:50,020 return to a vertical position the tethered system could also be perturbed 466 00:11:50,020 --> 00:11:50,030 tethered system could also be perturbed 467 00:11:50,030 --> 00:11:53,260 tethered system could also be perturbed off the vertical axis without any 468 00:11:53,260 --> 00:11:53,270 off the vertical axis without any 469 00:11:53,270 --> 00:11:55,450 off the vertical axis without any restoring force the system would rotate 470 00:11:55,450 --> 00:11:55,460 restoring force the system would rotate 471 00:11:55,460 --> 00:11:58,330 restoring force the system would rotate like these tethered apples but the 472 00:11:58,330 --> 00:11:58,340 like these tethered apples but the 473 00:11:58,340 --> 00:12:00,970 like these tethered apples but the tethered system stable equilibrium keeps 474 00:12:00,970 --> 00:12:00,980 tethered system stable equilibrium keeps 475 00:12:00,980 --> 00:12:04,360 tethered system stable equilibrium keeps it aligned along a vertical axis what 476 00:12:04,360 --> 00:12:04,370 it aligned along a vertical axis what 477 00:12:04,370 --> 00:12:06,250 it aligned along a vertical axis what causes the tethered system stable 478 00:12:06,250 --> 00:12:06,260 causes the tethered system stable 479 00:12:06,260 --> 00:12:08,980 causes the tethered system stable equilibrium and space well once again 480 00:12:08,980 --> 00:12:08,990 equilibrium and space well once again 481 00:12:08,990 --> 00:12:12,160 equilibrium and space well once again gravity is at work you see gravity pulls 482 00:12:12,160 --> 00:12:12,170 gravity is at work you see gravity pulls 483 00:12:12,170 --> 00:12:18,810 gravity is at work you see gravity pulls on both ends of the system 484 00:12:18,810 --> 00:12:18,820 485 00:12:18,820 --> 00:12:21,360 the pull on the satellite at the upper 486 00:12:21,360 --> 00:12:21,370 the pull on the satellite at the upper 487 00:12:21,370 --> 00:12:23,430 the pull on the satellite at the upper end of the tether makes the system want 488 00:12:23,430 --> 00:12:23,440 end of the tether makes the system want 489 00:12:23,440 --> 00:12:26,010 end of the tether makes the system want to depart from the vertical while a pole 490 00:12:26,010 --> 00:12:26,020 to depart from the vertical while a pole 491 00:12:26,020 --> 00:12:28,260 to depart from the vertical while a pole on the orbiter at the lower end makes 492 00:12:28,260 --> 00:12:28,270 on the orbiter at the lower end makes 493 00:12:28,270 --> 00:12:31,410 on the orbiter at the lower end makes the system return do you remember the 494 00:12:31,410 --> 00:12:31,420 the system return do you remember the 495 00:12:31,420 --> 00:12:34,410 the system return do you remember the gravity gradient the end closest to the 496 00:12:34,410 --> 00:12:34,420 gravity gradient the end closest to the 497 00:12:34,420 --> 00:12:36,990 gravity gradient the end closest to the earth feels the greatest acceleration so 498 00:12:36,990 --> 00:12:37,000 earth feels the greatest acceleration so 499 00:12:37,000 --> 00:12:39,360 earth feels the greatest acceleration so the system feels a net torque and the 500 00:12:39,360 --> 00:12:39,370 the system feels a net torque and the 501 00:12:39,370 --> 00:12:42,900 the system feels a net torque and the tether returns to the vertical it 502 00:12:42,900 --> 00:12:42,910 tether returns to the vertical it 503 00:12:42,910 --> 00:12:44,760 tether returns to the vertical it doesn't matter if the mass is at the end 504 00:12:44,760 --> 00:12:44,770 doesn't matter if the mass is at the end 505 00:12:44,770 --> 00:12:46,710 doesn't matter if the mass is at the end of the system are equal or not the 506 00:12:46,710 --> 00:12:46,720 of the system are equal or not the 507 00:12:46,720 --> 00:12:48,660 of the system are equal or not the gravity gradient is stabilizing the 508 00:12:48,660 --> 00:12:48,670 gravity gradient is stabilizing the 509 00:12:48,670 --> 00:12:51,630 gravity gradient is stabilizing the system but gravity gradient is only part 510 00:12:51,630 --> 00:12:51,640 system but gravity gradient is only part 511 00:12:51,640 --> 00:12:53,340 system but gravity gradient is only part of the story there's another force at 512 00:12:53,340 --> 00:12:53,350 of the story there's another force at 513 00:12:53,350 --> 00:12:56,250 of the story there's another force at work remember we saw that there is an 514 00:12:56,250 --> 00:12:56,260 work remember we saw that there is an 515 00:12:56,260 --> 00:12:58,620 work remember we saw that there is an approximate force of 26 Newtons 516 00:12:58,620 --> 00:12:58,630 approximate force of 26 Newtons 517 00:12:58,630 --> 00:13:01,080 approximate force of 26 Newtons for the gravity gradient over a 20 518 00:13:01,080 --> 00:13:01,090 for the gravity gradient over a 20 519 00:13:01,090 --> 00:13:02,270 for the gravity gradient over a 20 kilometer tether 520 00:13:02,270 --> 00:13:02,280 kilometer tether 521 00:13:02,280 --> 00:13:05,490 kilometer tether well when the tether is extended 20 522 00:13:05,490 --> 00:13:05,500 well when the tether is extended 20 523 00:13:05,500 --> 00:13:07,890 well when the tether is extended 20 kilometers our force measuring device 524 00:13:07,890 --> 00:13:07,900 kilometers our force measuring device 525 00:13:07,900 --> 00:13:11,450 kilometers our force measuring device measures 40 Newtons not 26 Newtons 526 00:13:11,450 --> 00:13:11,460 measures 40 Newtons not 26 Newtons 527 00:13:11,460 --> 00:13:15,140 measures 40 Newtons not 26 Newtons now where did this extra force come from 528 00:13:15,140 --> 00:13:15,150 now where did this extra force come from 529 00:13:15,150 --> 00:13:19,620 now where did this extra force come from here is a clue it's the same force we 530 00:13:19,620 --> 00:13:19,630 here is a clue it's the same force we 531 00:13:19,630 --> 00:13:22,800 here is a clue it's the same force we feel when we will an object around on a 532 00:13:22,800 --> 00:13:22,810 feel when we will an object around on a 533 00:13:22,810 --> 00:13:25,980 feel when we will an object around on a string and the strain stretches the 534 00:13:25,980 --> 00:13:25,990 string and the strain stretches the 535 00:13:25,990 --> 00:13:28,500 string and the strain stretches the faster the speed the harder the force 536 00:13:28,500 --> 00:13:28,510 faster the speed the harder the force 537 00:13:28,510 --> 00:13:31,050 faster the speed the harder the force tries to fling the object away from the 538 00:13:31,050 --> 00:13:31,060 tries to fling the object away from the 539 00:13:31,060 --> 00:13:35,920 tries to fling the object away from the center 540 00:13:35,920 --> 00:13:35,930 541 00:13:35,930 --> 00:13:39,640 as you have seen gravity helps keep the 542 00:13:39,640 --> 00:13:39,650 as you have seen gravity helps keep the 543 00:13:39,650 --> 00:13:41,360 as you have seen gravity helps keep the Tetra vertical 544 00:13:41,360 --> 00:13:41,370 Tetra vertical 545 00:13:41,370 --> 00:13:43,640 Tetra vertical and you can actually calculate this 546 00:13:43,640 --> 00:13:43,650 and you can actually calculate this 547 00:13:43,650 --> 00:13:46,550 and you can actually calculate this expert force and it turns out it's about 548 00:13:46,550 --> 00:13:46,560 expert force and it turns out it's about 549 00:13:46,560 --> 00:13:50,170 expert force and it turns out it's about half the gravity gradient force a 550 00:13:50,170 --> 00:13:50,180 half the gravity gradient force a 551 00:13:50,180 --> 00:13:52,790 half the gravity gradient force a significant effect 552 00:13:52,790 --> 00:13:52,800 significant effect 553 00:13:52,800 --> 00:13:57,150 significant effect therefore as it orbits the earth it is 554 00:13:57,150 --> 00:13:57,160 therefore as it orbits the earth it is 555 00:13:57,160 --> 00:13:59,820 therefore as it orbits the earth it is actually rotating once per orbit about 556 00:13:59,820 --> 00:13:59,830 actually rotating once per orbit about 557 00:13:59,830 --> 00:14:03,390 actually rotating once per orbit about its center of mass creating this extra 558 00:14:03,390 --> 00:14:03,400 its center of mass creating this extra 559 00:14:03,400 --> 00:14:07,830 its center of mass creating this extra force that stretches the tether we can 560 00:14:07,830 --> 00:14:07,840 force that stretches the tether we can 561 00:14:07,840 --> 00:14:11,250 force that stretches the tether we can see it in action another way if we have 562 00:14:11,250 --> 00:14:11,260 see it in action another way if we have 563 00:14:11,260 --> 00:14:13,830 see it in action another way if we have one of our crews spin a bucket of water 564 00:14:13,830 --> 00:14:13,840 one of our crews spin a bucket of water 565 00:14:13,840 --> 00:14:17,250 one of our crews spin a bucket of water around in a circle the water will stay 566 00:14:17,250 --> 00:14:17,260 around in a circle the water will stay 567 00:14:17,260 --> 00:14:19,650 around in a circle the water will stay inside a bucket as long as the motion 568 00:14:19,650 --> 00:14:19,660 inside a bucket as long as the motion 569 00:14:19,660 --> 00:14:23,880 inside a bucket as long as the motion continues stop the motion the force 570 00:14:23,880 --> 00:14:23,890 continues stop the motion the force 571 00:14:23,890 --> 00:14:27,480 continues stop the motion the force disappears and the water obeys the law 572 00:14:27,480 --> 00:14:27,490 disappears and the water obeys the law 573 00:14:27,490 --> 00:14:30,750 disappears and the water obeys the law of gravitational attraction like the 574 00:14:30,750 --> 00:14:30,760 of gravitational attraction like the 575 00:14:30,760 --> 00:14:32,790 of gravitational attraction like the gravity gradient force it is also 576 00:14:32,790 --> 00:14:32,800 gravity gradient force it is also 577 00:14:32,800 --> 00:14:34,860 gravity gradient force it is also proportional to the length of the tether 578 00:14:34,860 --> 00:14:34,870 proportional to the length of the tether 579 00:14:34,870 --> 00:14:37,560 proportional to the length of the tether as long as the rate of rotation stays 580 00:14:37,560 --> 00:14:37,570 as long as the rate of rotation stays 581 00:14:37,570 --> 00:14:39,740 as long as the rate of rotation stays constant 582 00:14:39,740 --> 00:14:39,750 constant 583 00:14:39,750 --> 00:14:44,100 constant and speaking of constants we've always 584 00:14:44,100 --> 00:14:44,110 and speaking of constants we've always 585 00:14:44,110 --> 00:14:46,650 and speaking of constants we've always assumed that the tether remains at a 586 00:14:46,650 --> 00:14:46,660 assumed that the tether remains at a 587 00:14:46,660 --> 00:14:48,930 assumed that the tether remains at a constant length and this is not always 588 00:14:48,930 --> 00:14:48,940 constant length and this is not always 589 00:14:48,940 --> 00:14:53,370 constant length and this is not always the case when we lengthened or shortened 590 00:14:53,370 --> 00:14:53,380 the case when we lengthened or shortened 591 00:14:53,380 --> 00:14:55,560 the case when we lengthened or shortened the tether another physics principle 592 00:14:55,560 --> 00:14:55,570 the tether another physics principle 593 00:14:55,570 --> 00:14:57,810 the tether another physics principle that you've heard of comes into play and 594 00:14:57,810 --> 00:14:57,820 that you've heard of comes into play and 595 00:14:57,820 --> 00:15:02,310 that you've heard of comes into play and that angular momentum you see it here in 596 00:15:02,310 --> 00:15:02,320 that angular momentum you see it here in 597 00:15:02,320 --> 00:15:05,430 that angular momentum you see it here in the motion of the skater angular 598 00:15:05,430 --> 00:15:05,440 the motion of the skater angular 599 00:15:05,440 --> 00:15:07,950 the motion of the skater angular momentum is the product of an object's 600 00:15:07,950 --> 00:15:07,960 momentum is the product of an object's 601 00:15:07,960 --> 00:15:10,880 momentum is the product of an object's rotational inertia and angular velocity 602 00:15:10,880 --> 00:15:10,890 rotational inertia and angular velocity 603 00:15:10,890 --> 00:15:16,440 rotational inertia and angular velocity about a particular axis when the object 604 00:15:16,440 --> 00:15:16,450 about a particular axis when the object 605 00:15:16,450 --> 00:15:18,390 about a particular axis when the object changes its mass distribution the 606 00:15:18,390 --> 00:15:18,400 changes its mass distribution the 607 00:15:18,400 --> 00:15:21,180 changes its mass distribution the angular momentum stays the same but the 608 00:15:21,180 --> 00:15:21,190 angular momentum stays the same but the 609 00:15:21,190 --> 00:15:25,530 angular momentum stays the same but the rotation rate changes we call this the 610 00:15:25,530 --> 00:15:25,540 rotation rate changes we call this the 611 00:15:25,540 --> 00:15:28,860 rotation rate changes we call this the conservation of angular momentum and you 612 00:15:28,860 --> 00:15:28,870 conservation of angular momentum and you 613 00:15:28,870 --> 00:15:30,630 conservation of angular momentum and you can see for yourself how this principle 614 00:15:30,630 --> 00:15:30,640 can see for yourself how this principle 615 00:15:30,640 --> 00:15:35,310 can see for yourself how this principle works stand on a turntable with your 616 00:15:35,310 --> 00:15:35,320 works stand on a turntable with your 617 00:15:35,320 --> 00:15:37,890 works stand on a turntable with your arms outstretched and weights in your 618 00:15:37,890 --> 00:15:37,900 arms outstretched and weights in your 619 00:15:37,900 --> 00:15:39,560 arms outstretched and weights in your hands 620 00:15:39,560 --> 00:15:39,570 hands 621 00:15:39,570 --> 00:15:43,220 hands have someone start you spinning now 622 00:15:43,220 --> 00:15:43,230 have someone start you spinning now 623 00:15:43,230 --> 00:15:47,449 have someone start you spinning now bring your arms in you speed up that's 624 00:15:47,449 --> 00:15:47,459 bring your arms in you speed up that's 625 00:15:47,459 --> 00:15:48,680 bring your arms in you speed up that's because the more the mass is 626 00:15:48,680 --> 00:15:48,690 because the more the mass is 627 00:15:48,690 --> 00:15:50,480 because the more the mass is concentrated towards the center of mass 628 00:15:50,480 --> 00:15:50,490 concentrated towards the center of mass 629 00:15:50,490 --> 00:15:55,040 concentrated towards the center of mass the faster the mass spins now let's see 630 00:15:55,040 --> 00:15:55,050 the faster the mass spins now let's see 631 00:15:55,050 --> 00:15:57,379 the faster the mass spins now let's see how this part of physics relates to our 632 00:15:57,379 --> 00:15:57,389 how this part of physics relates to our 633 00:15:57,389 --> 00:16:01,970 how this part of physics relates to our spaceship and the data satellite when 634 00:16:01,970 --> 00:16:01,980 spaceship and the data satellite when 635 00:16:01,980 --> 00:16:04,280 spaceship and the data satellite when the tether is pulled in the rotating 636 00:16:04,280 --> 00:16:04,290 the tether is pulled in the rotating 637 00:16:04,290 --> 00:16:06,559 the tether is pulled in the rotating mass of the system is concentrated into 638 00:16:06,559 --> 00:16:06,569 mass of the system is concentrated into 639 00:16:06,569 --> 00:16:10,249 mass of the system is concentrated into a smaller area and the system tries to 640 00:16:10,249 --> 00:16:10,259 a smaller area and the system tries to 641 00:16:10,259 --> 00:16:13,490 a smaller area and the system tries to speed up just like the skater when the 642 00:16:13,490 --> 00:16:13,500 speed up just like the skater when the 643 00:16:13,500 --> 00:16:15,680 speed up just like the skater when the tether is let out the mass is 644 00:16:15,680 --> 00:16:15,690 tether is let out the mass is 645 00:16:15,690 --> 00:16:18,079 tether is let out the mass is distributed in a bigger area and the 646 00:16:18,079 --> 00:16:18,089 distributed in a bigger area and the 647 00:16:18,089 --> 00:16:20,990 distributed in a bigger area and the orbiter and tether system slow down just 648 00:16:20,990 --> 00:16:21,000 orbiter and tether system slow down just 649 00:16:21,000 --> 00:16:22,850 orbiter and tether system slow down just like the students slow down 650 00:16:22,850 --> 00:16:22,860 like the students slow down 651 00:16:22,860 --> 00:16:25,460 like the students slow down when she extended her arms in the 652 00:16:25,460 --> 00:16:25,470 when she extended her arms in the 653 00:16:25,470 --> 00:16:27,290 when she extended her arms in the orbiter we see this from a slightly 654 00:16:27,290 --> 00:16:27,300 orbiter we see this from a slightly 655 00:16:27,300 --> 00:16:30,379 orbiter we see this from a slightly different perspective because we are 656 00:16:30,379 --> 00:16:30,389 different perspective because we are 657 00:16:30,389 --> 00:16:34,370 different perspective because we are part of the rotating system remember 658 00:16:34,370 --> 00:16:34,380 part of the rotating system remember 659 00:16:34,380 --> 00:16:36,259 part of the rotating system remember during most of the mission for 660 00:16:36,259 --> 00:16:36,269 during most of the mission for 661 00:16:36,269 --> 00:16:38,870 during most of the mission for scientific reasons the orbiter is moving 662 00:16:38,870 --> 00:16:38,880 scientific reasons the orbiter is moving 663 00:16:38,880 --> 00:16:43,040 scientific reasons the orbiter is moving with the tail forward do you notice how 664 00:16:43,040 --> 00:16:43,050 with the tail forward do you notice how 665 00:16:43,050 --> 00:16:45,350 with the tail forward do you notice how from our point of view the satellite 666 00:16:45,350 --> 00:16:45,360 from our point of view the satellite 667 00:16:45,360 --> 00:16:47,030 from our point of view the satellite moves forward with respect to our 668 00:16:47,030 --> 00:16:47,040 moves forward with respect to our 669 00:16:47,040 --> 00:16:50,449 moves forward with respect to our direction of motion and moves backward 670 00:16:50,449 --> 00:16:50,459 direction of motion and moves backward 671 00:16:50,459 --> 00:16:52,540 direction of motion and moves backward with respect to our direction of motion 672 00:16:52,540 --> 00:16:52,550 with respect to our direction of motion 673 00:16:52,550 --> 00:16:57,350 with respect to our direction of motion when it's let out and this is called the 674 00:16:57,350 --> 00:16:57,360 when it's let out and this is called the 675 00:16:57,360 --> 00:17:00,319 when it's let out and this is called the Coriolis effect and it occurs in all 676 00:17:00,319 --> 00:17:00,329 Coriolis effect and it occurs in all 677 00:17:00,329 --> 00:17:04,220 Coriolis effect and it occurs in all rotating systems as a consequence of the 678 00:17:04,220 --> 00:17:04,230 rotating systems as a consequence of the 679 00:17:04,230 --> 00:17:05,870 rotating systems as a consequence of the conservation of angular momentum 680 00:17:05,870 --> 00:17:05,880 conservation of angular momentum 681 00:17:05,880 --> 00:17:08,960 conservation of angular momentum it is the tendency of objects in 682 00:17:08,960 --> 00:17:08,970 it is the tendency of objects in 683 00:17:08,970 --> 00:17:14,000 it is the tendency of objects in rotating systems to move in a curve as 684 00:17:14,000 --> 00:17:14,010 rotating systems to move in a curve as 685 00:17:14,010 --> 00:17:17,370 rotating systems to move in a curve as opposed to a straight line 686 00:17:17,370 --> 00:17:17,380 687 00:17:17,380 --> 00:17:20,680 we'll try to throw a ball from someone 688 00:17:20,680 --> 00:17:20,690 we'll try to throw a ball from someone 689 00:17:20,690 --> 00:17:23,020 we'll try to throw a ball from someone on one side of a merry-go-round 690 00:17:23,020 --> 00:17:23,030 on one side of a merry-go-round 691 00:17:23,030 --> 00:17:25,270 on one side of a merry-go-round to someone on the other side of the 692 00:17:25,270 --> 00:17:25,280 to someone on the other side of the 693 00:17:25,280 --> 00:17:28,690 to someone on the other side of the merry-go-round as we can see the ball is 694 00:17:28,690 --> 00:17:28,700 merry-go-round as we can see the ball is 695 00:17:28,700 --> 00:17:31,630 merry-go-round as we can see the ball is thrown in a straight line but not from 696 00:17:31,630 --> 00:17:31,640 thrown in a straight line but not from 697 00:17:31,640 --> 00:17:34,300 thrown in a straight line but not from this point of view here it appears the 698 00:17:34,300 --> 00:17:34,310 this point of view here it appears the 699 00:17:34,310 --> 00:17:38,110 this point of view here it appears the balls trajectory is curving and this is 700 00:17:38,110 --> 00:17:38,120 balls trajectory is curving and this is 701 00:17:38,120 --> 00:17:39,880 balls trajectory is curving and this is what makes the satellite move backward 702 00:17:39,880 --> 00:17:39,890 what makes the satellite move backward 703 00:17:39,890 --> 00:17:44,470 what makes the satellite move backward or forward as we reel it out or in the 704 00:17:44,470 --> 00:17:44,480 or forward as we reel it out or in the 705 00:17:44,480 --> 00:17:47,110 or forward as we reel it out or in the Coriolis effect is what makes hurricanes 706 00:17:47,110 --> 00:17:47,120 Coriolis effect is what makes hurricanes 707 00:17:47,120 --> 00:17:50,790 Coriolis effect is what makes hurricanes spiral and other weather systems curved 708 00:17:50,790 --> 00:17:50,800 spiral and other weather systems curved 709 00:17:50,800 --> 00:17:53,980 spiral and other weather systems curved we won't go into the mathematics here 710 00:17:53,980 --> 00:17:53,990 we won't go into the mathematics here 711 00:17:53,990 --> 00:17:56,410 we won't go into the mathematics here except to say that the larger the tether 712 00:17:56,410 --> 00:17:56,420 except to say that the larger the tether 713 00:17:56,420 --> 00:17:59,740 except to say that the larger the tether reel out or reeling rates the greater 714 00:17:59,740 --> 00:17:59,750 reel out or reeling rates the greater 715 00:17:59,750 --> 00:18:01,900 reel out or reeling rates the greater the backward or forward motion of the 716 00:18:01,900 --> 00:18:01,910 the backward or forward motion of the 717 00:18:01,910 --> 00:18:08,650 the backward or forward motion of the satellite from the vertical so let's 718 00:18:08,650 --> 00:18:08,660 satellite from the vertical so let's 719 00:18:08,660 --> 00:18:10,660 satellite from the vertical so let's review the aspects of tether dynamics 720 00:18:10,660 --> 00:18:10,670 review the aspects of tether dynamics 721 00:18:10,670 --> 00:18:14,100 review the aspects of tether dynamics that we've looked at so far gravity 722 00:18:14,100 --> 00:18:14,110 that we've looked at so far gravity 723 00:18:14,110 --> 00:18:18,370 that we've looked at so far gravity center of mass and angular momentum all 724 00:18:18,370 --> 00:18:18,380 center of mass and angular momentum all 725 00:18:18,380 --> 00:18:20,560 center of mass and angular momentum all of these concepts are studied in your 726 00:18:20,560 --> 00:18:20,570 of these concepts are studied in your 727 00:18:20,570 --> 00:18:23,620 of these concepts are studied in your first-year physics course yet all of it 728 00:18:23,620 --> 00:18:23,630 first-year physics course yet all of it 729 00:18:23,630 --> 00:18:25,960 first-year physics course yet all of it is used in a way like nothing you've 730 00:18:25,960 --> 00:18:25,970 is used in a way like nothing you've 731 00:18:25,970 --> 00:18:30,430 is used in a way like nothing you've ever seen before and there are even more 732 00:18:30,430 --> 00:18:30,440 ever seen before and there are even more 733 00:18:30,440 --> 00:18:35,110 ever seen before and there are even more uses of tether technology on orbit we 734 00:18:35,110 --> 00:18:35,120 uses of tether technology on orbit we 735 00:18:35,120 --> 00:18:37,060 uses of tether technology on orbit we found we could use the tether to 736 00:18:37,060 --> 00:18:37,070 found we could use the tether to 737 00:18:37,070 --> 00:18:40,060 found we could use the tether to generate electricity as the copper cord 738 00:18:40,060 --> 00:18:40,070 generate electricity as the copper cord 739 00:18:40,070 --> 00:18:42,220 generate electricity as the copper cord tether flew through the Earth's magnetic 740 00:18:42,220 --> 00:18:42,230 tether flew through the Earth's magnetic 741 00:18:42,230 --> 00:18:43,260 tether flew through the Earth's magnetic field 742 00:18:43,260 --> 00:18:43,270 field 743 00:18:43,270 --> 00:18:46,750 field so the question left is what can we use 744 00:18:46,750 --> 00:18:46,760 so the question left is what can we use 745 00:18:46,760 --> 00:18:51,610 so the question left is what can we use this to other technology for we could 746 00:18:51,610 --> 00:18:51,620 this to other technology for we could 747 00:18:51,620 --> 00:18:54,430 this to other technology for we could use tethers to directly study parts of 748 00:18:54,430 --> 00:18:54,440 use tethers to directly study parts of 749 00:18:54,440 --> 00:18:56,350 use tethers to directly study parts of the Earth's atmosphere that we can't 750 00:18:56,350 --> 00:18:56,360 the Earth's atmosphere that we can't 751 00:18:56,360 --> 00:18:59,490 the Earth's atmosphere that we can't reach by any present-day technology 752 00:18:59,490 --> 00:18:59,500 reach by any present-day technology 753 00:18:59,500 --> 00:19:01,720 reach by any present-day technology tethers could reduce the need for 754 00:19:01,720 --> 00:19:01,730 tethers could reduce the need for 755 00:19:01,730 --> 00:19:05,200 tethers could reduce the need for chemical fuels in space boosting objects 756 00:19:05,200 --> 00:19:05,210 chemical fuels in space boosting objects 757 00:19:05,210 --> 00:19:08,020 chemical fuels in space boosting objects to stay in orbit and assisting others to 758 00:19:08,020 --> 00:19:08,030 to stay in orbit and assisting others to 759 00:19:08,030 --> 00:19:11,830 to stay in orbit and assisting others to deorbit and engineers could use the open 760 00:19:11,830 --> 00:19:11,840 deorbit and engineers could use the open 761 00:19:11,840 --> 00:19:13,510 deorbit and engineers could use the open wind tunnel of the Earth's upper 762 00:19:13,510 --> 00:19:13,520 wind tunnel of the Earth's upper 763 00:19:13,520 --> 00:19:16,330 wind tunnel of the Earth's upper atmosphere for testing the hypersonic 764 00:19:16,330 --> 00:19:16,340 atmosphere for testing the hypersonic 765 00:19:16,340 --> 00:19:18,700 atmosphere for testing the hypersonic aerodynamics of reentry vehicles and 766 00:19:18,700 --> 00:19:18,710 aerodynamics of reentry vehicles and 767 00:19:18,710 --> 00:19:21,700 aerodynamics of reentry vehicles and aerobraking technology 768 00:19:21,700 --> 00:19:21,710 aerobraking technology 769 00:19:21,710 --> 00:19:24,880 aerobraking technology it's even possible that one day tether 770 00:19:24,880 --> 00:19:24,890 it's even possible that one day tether 771 00:19:24,890 --> 00:19:27,250 it's even possible that one day tether driven electric cable cars will ferry 772 00:19:27,250 --> 00:19:27,260 driven electric cable cars will ferry 773 00:19:27,260 --> 00:19:29,380 driven electric cable cars will ferry space travelers from earth to 774 00:19:29,380 --> 00:19:29,390 space travelers from earth to 775 00:19:29,390 --> 00:19:33,970 space travelers from earth to geostationary orbit what uses of tether 776 00:19:33,970 --> 00:19:33,980 geostationary orbit what uses of tether 777 00:19:33,980 --> 00:19:37,270 geostationary orbit what uses of tether technology can you think of the limits 778 00:19:37,270 --> 00:19:37,280 technology can you think of the limits 779 00:19:37,280 --> 00:19:42,640 technology can you think of the limits are not of physics but of the human mind