English subtitles for clip: File:0762 Spinning Levers 04 45 20 00 3mb.webm
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1 00:00:06,245 --> 00:00:08,041 [fanfare] 2 00:00:20,616 --> 00:00:22,364 [fanfare fades] 3 00:00:23,656 --> 00:00:26,189 Meet Mr. Archimedes of Ancient Greece. 4 00:00:26,821 --> 00:00:28,501 Long ago, Archi said, 5 00:00:28,525 --> 00:00:32,223 "Give me a lever long enough, 6 00:00:32,247 --> 00:00:35,438 and I can move the world." 7 00:00:35,462 --> 00:00:40,686 What Archimedes meant was that the power of a lever is practically unlimited. 8 00:00:41,093 --> 00:00:45,253 Today, almost everyone uses some form of lever in his daily work. 9 00:00:45,799 --> 00:00:49,703 The familiar can opener is a lever with a sharp cutting edge. 10 00:00:50,282 --> 00:00:54,121 The playground seesaw is just a simple lever too. 11 00:00:54,721 --> 00:00:57,893 It takes a lot of force to start a freight car moving, 12 00:00:57,917 --> 00:01:03,582 yet the railroad man can start the heaviest freight cars easily with a pinch bar, 13 00:01:03,606 --> 00:01:06,659 a powerful lever which turns the wheel. 14 00:01:07,580 --> 00:01:12,060 Just like old boy, here's a place where a lever comes in mighty handy. 15 00:01:12,617 --> 00:01:14,964 Let's take the simplest kind of lever: 16 00:01:14,988 --> 00:01:19,264 a rigid bar working on a fixed support called a fulcrum. 17 00:01:19,848 --> 00:01:23,176 One end of this lever is twice as long as the other. 18 00:01:23,482 --> 00:01:26,268 Let's put a ten-pound weight on this end, 19 00:01:26,292 --> 00:01:28,913 and now we'll put half as much weight on this end. 20 00:01:29,285 --> 00:01:31,948 Five pounds balance ten. 21 00:01:33,066 --> 00:01:37,437 If we have twenty-five pounds to lift, we just use a longer lever. 22 00:01:37,461 --> 00:01:41,171 The five pounds will now balance five times as much. 23 00:01:41,196 --> 00:01:44,130 Let's raise the lever in the air, 24 00:01:44,154 --> 00:01:47,216 change its shape a little, and we have a crank. 25 00:01:47,904 --> 00:01:51,040 Or we add a second lever and have a double crank. 26 00:01:52,083 --> 00:01:55,274 Now the short arm moves one-fourth the distance, 27 00:01:55,298 --> 00:01:57,935 but we get four times the force. 28 00:01:58,334 --> 00:02:02,419 If we want continuous motion, we need more arms. 29 00:02:03,302 --> 00:02:05,235 Now we have levers that turn. 30 00:02:06,253 --> 00:02:09,342 The larger paddle wheel makes fewer turns 31 00:02:09,366 --> 00:02:11,366 but it delivers more force. 32 00:02:12,686 --> 00:02:16,654 A paddle wheel is nothing but a never-ending series of levers. 33 00:02:17,114 --> 00:02:19,182 We can make the wheels stronger 34 00:02:19,206 --> 00:02:22,112 and lessen friction where the wheels touch each other 35 00:02:22,136 --> 00:02:25,717 by rounding off the edges and shaping them into teeth 36 00:02:25,741 --> 00:02:27,741 that will slide in and out smoothly. 37 00:02:28,483 --> 00:02:32,490 Now, the power flows smoothly and continuously 38 00:02:32,514 --> 00:02:35,108 through spinning leverage of gear wheels. 39 00:02:35,667 --> 00:02:38,611 Gears are made in many kinds and many sizes – 40 00:02:38,820 --> 00:02:41,379 little gears, big gears, 41 00:02:41,974 --> 00:02:44,770 worm gears, bevel gears 42 00:02:44,794 --> 00:02:46,794 and even lopsided gears. 43 00:02:47,552 --> 00:02:50,802 Over a hundred million gears are spinning over the roads 44 00:02:50,826 --> 00:02:53,118 in the transmissions of our automobiles. 45 00:02:54,044 --> 00:02:58,211 The transmission is located right at the bottom of the gear shift lever. 46 00:02:58,668 --> 00:03:01,436 Let's start from scratch and put together a model 47 00:03:01,460 --> 00:03:04,495 of the gears that we shift in our motor car. 48 00:03:04,914 --> 00:03:07,814 The shaft on the left comes from the engine. 49 00:03:08,328 --> 00:03:12,424 The shaft on the right carries the power back to the rear wheels. 50 00:03:13,202 --> 00:03:15,505 To connect these two with gears, 51 00:03:15,529 --> 00:03:19,281 we'll need another shaft known as a countershaft. 52 00:03:20,731 --> 00:03:26,200 These two gears carry the power from the engine shaft to the countershaft, 53 00:03:26,224 --> 00:03:29,547 and are always connected or in mesh. 54 00:03:31,875 --> 00:03:35,973 This gear on the drive shaft going to the wheels 55 00:03:36,560 --> 00:03:39,076 is free to turn around the shaft. 56 00:03:40,397 --> 00:03:44,610 We'll put it in mesh with another gear on the countershaft. 57 00:03:44,756 --> 00:03:47,406 These gears are always in mesh... 58 00:03:51,249 --> 00:03:54,149 and keep turning while the engine is running. 59 00:03:57,184 --> 00:04:00,051 To switch from one set of gears to another, 60 00:04:00,075 --> 00:04:03,260 our transmission needs a short shaft like this, 61 00:04:03,284 --> 00:04:05,284 known as a clutch sleeve. 62 00:04:07,438 --> 00:04:12,503 It cannot turn on the drive shaft, but it is free to slide back and forth. 63 00:04:15,565 --> 00:04:18,523 On the sleeve, we'll note a large gear, 64 00:04:20,187 --> 00:04:23,193 which we can shift back and forth to mesh with 65 00:04:23,217 --> 00:04:26,626 the small gear in the middle of the countershaft. 66 00:04:31,495 --> 00:04:33,432 We are now in neutral. 67 00:04:34,050 --> 00:04:38,364 The gears that are always in mesh are turning over with the engine, 68 00:04:38,388 --> 00:04:42,260 but the shaft to the rear wheels is standing still. 69 00:04:42,932 --> 00:04:47,028 A three-thousand-pound automobile takes a lot of force to start. 70 00:04:49,979 --> 00:04:53,491 So in low speed, we get the greatest leverage 71 00:04:53,515 --> 00:04:56,393 by letting the smallest gear on the countershaft 72 00:04:56,417 --> 00:04:58,921 turn the largest gear on the drive shaft. 73 00:05:00,730 --> 00:05:03,781 The engine on this model is running at a constant speed 74 00:05:03,805 --> 00:05:05,805 of ninety revolutions a minute. 75 00:05:07,341 --> 00:05:12,263 With low gears in mesh, the rear wheel is turning at thirty revolutions a minute, 76 00:05:12,287 --> 00:05:17,528 about a third the speed of the engine, but with three times the force. 77 00:05:17,927 --> 00:05:21,703 The power is going through these gears in the transmission. 78 00:05:32,337 --> 00:05:36,188 After we've started the car rolling, we want fast pickup, 79 00:05:36,930 --> 00:05:40,704 so we shift into second by sliding the sleeve backward 80 00:05:40,728 --> 00:05:44,555 to mesh with this gear on the shaft to the rear wheels. 81 00:05:45,157 --> 00:05:48,897 The wheel is now turning at sixty revolutions a minute, 82 00:05:48,921 --> 00:05:51,720 and the power flows through these gears. 83 00:05:59,203 --> 00:06:03,792 For higher speeds, we let the power go directly to the rear wheels 84 00:06:04,644 --> 00:06:07,534 We shift the sleeve forward 85 00:06:07,558 --> 00:06:10,448 so that it meshes with the shaft from the engine. 86 00:06:11,121 --> 00:06:15,133 The power travels straight from the engine to the drive shaft. 87 00:06:15,946 --> 00:06:18,904 Now the shaft to the wheels is turning 88 00:06:18,928 --> 00:06:21,233 at ninety revolutions a minute: 89 00:06:21,704 --> 00:06:23,637 the same speed as the engine. 90 00:06:24,659 --> 00:06:26,226 But here's a problem: 91 00:06:26,250 --> 00:06:30,503 an automobile must be able to go backward as well as forward, 92 00:06:31,261 --> 00:06:33,823 so we add one more set of gears to 93 00:06:33,847 --> 00:06:36,800 reverse the shaft to the rear wheels. 94 00:06:37,395 --> 00:06:39,770 With the gears shifted into reverse, 95 00:06:41,145 --> 00:06:45,801 the power travels through the transmission in a path like this. 96 00:06:47,099 --> 00:06:50,960 We now have three sets of spinning levers for going forward, 97 00:06:50,984 --> 00:06:53,070 and one for reverse. 98 00:06:53,383 --> 00:06:57,543 With a gear shift lever, we can shift to any set of gears we wish. 99 00:06:58,707 --> 00:07:04,304 But with all these spinning levers in the transmission came noise and wear. 100 00:07:04,609 --> 00:07:08,073 Experts could shift gears quietly by careful timing 101 00:07:08,097 --> 00:07:10,784 of the gear shift and the engine speeds, 102 00:07:10,808 --> 00:07:13,070 [gears screech] but most of us made plenty of noise 103 00:07:13,532 --> 00:07:16,620 until new engineering developments made possible 104 00:07:16,644 --> 00:07:19,484 a long series of improvements that followed. 105 00:07:20,042 --> 00:07:22,508 When we shifted gears, we got a clash 106 00:07:23,205 --> 00:07:26,257 because the gears were not running at the same speed – 107 00:07:26,281 --> 00:07:29,142 in other words, not synchronized. 108 00:07:30,377 --> 00:07:33,621 So engineers set to work to develop a synchronizer. 109 00:07:34,200 --> 00:07:38,490 The synchronizer works like a cork twisted into the top of a bottle. 110 00:07:38,514 --> 00:07:42,599 The cork will turn until it is so tight that the bottle turns with it. 111 00:07:43,107 --> 00:07:45,891 Synchromesh works the same way. 112 00:07:46,255 --> 00:07:48,911 When we shift into second or high, 113 00:07:48,935 --> 00:07:54,056 the synchronizer brings the gears to the same speed before they come together. 114 00:07:54,434 --> 00:07:59,426 The drums won't let the gears shift unless they are turning at the same speed. 115 00:08:00,567 --> 00:08:03,656 When the gears come together, there is no clash, 116 00:08:03,680 --> 00:08:07,258 and the shift is made quietly and easily. 117 00:08:11,852 --> 00:08:14,719 In the transmission of the up-to-date automobile, 118 00:08:14,743 --> 00:08:19,653 we have a powerful low gear to give us a strong spinning leverage in starting. 119 00:08:19,943 --> 00:08:23,911 A fast-turning motor must set the weight of the car in motion. 120 00:08:25,343 --> 00:08:29,635 In second speed, we can change leverage to get going fast 121 00:08:29,659 --> 00:08:31,846 at the same engine speed. 122 00:08:31,870 --> 00:08:36,085 With the leverage of third gear, power goes directly to the rear wheels 123 00:08:36,109 --> 00:08:38,523 and we can go as fast as we want. 124 00:08:38,547 --> 00:08:43,804 Now every driver can shift gears at any time, regardless of speed. 125 00:08:44,371 --> 00:08:48,355 Here is a hill that will give us a real chance to see how smoothly 126 00:08:48,379 --> 00:08:53,021 and reliably our spinning levers work in our automobile transmission. 127 00:08:53,756 --> 00:08:59,138 This driver is going to let her car gain a speed of sixty miles an hour down the hill. 128 00:09:07,200 --> 00:09:09,997 [same fanfare as before plays] 129 00:09:18,491 --> 00:09:22,579 Then she will shift into second speed and bring her car easily 130 00:09:22,603 --> 00:09:27,379 and safely under control before it reaches the bottom of the hill. 131 00:09:28,442 --> 00:09:29,962 [fanfare continues] 132 00:09:36,750 --> 00:09:38,833 [fanfare finalies]