English subtitles for clip: File:The Engineering of the Drinking Bird.webm
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1 00:00:05,230 --> 00:00:08,130 This toy has fascinated me since childhood. 2 00:00:08,130 --> 00:00:10,100 To me its motion is almost hypnotic. 3 00:00:10,100 --> 00:00:11,980 Here’s how it operates. 4 00:00:11,980 --> 00:00:16,280 Wet the bird’s beak thoroughly with room temperature water — the opaque container 5 00:00:16,280 --> 00:00:21,230 makes it looked chilled, but it isn’t ... then stand it up right . . . It’ll take a few 6 00:00:21,230 --> 00:00:25,860 seconds for it to start drinking . . . Notice that all of the action right now takes place 7 00:00:25,859 --> 00:00:27,829 in the stem here. 8 00:00:27,830 --> 00:00:32,650 As I speed up the action you see liquid rising and the bird rocking back and forth. 9 00:00:32,650 --> 00:00:36,240 If I return to normal speed, you can see the bird slowly … 10 00:00:36,240 --> 00:00:38,240 very, very slowly …. 11 00:00:39,180 --> 00:00:40,300 Rock forward ... 12 00:00:40,380 --> 00:00:44,440 Until it takes a drink, which it will do again and again. 13 00:00:44,440 --> 00:00:50,580 In this video I’ll detail the bird’s clever engineering design, explain how it uses thermodynamics, 14 00:00:50,580 --> 00:00:56,200 and link its action to some of the greatest and most impactful devices created by engineers. 15 00:00:56,200 --> 00:01:01,000 This toy has long history, but its current incarnation is due to Miles V. Sullivan, 16 00:01:01,040 --> 00:01:03,040 a scientist at Bell Labs. 17 00:01:03,040 --> 00:01:06,300 He specialized in methods of manufacturing semiconductors, 18 00:01:06,300 --> 00:01:09,460 but as a sideline invented toys. 19 00:01:09,470 --> 00:01:13,830 Its reported that this bird delighted U.S. President Herbert Hoover, an engineer, who 20 00:01:13,831 --> 00:01:18,911 failed to figure out how it worked, and it also defeated the great scientist Albert Einstein, 21 00:01:18,910 --> 00:01:21,860 who spent three and half months studying it. 22 00:01:21,860 --> 00:01:25,140 Its reported that he refused to take the bird apart. 23 00:01:25,140 --> 00:01:29,080 With the benefit of hindsight, let’s start by exploring how it works and examining the 24 00:01:29,080 --> 00:01:31,120 key engineering design aspects. 25 00:01:31,120 --> 00:01:35,900 First, let’s ask is the water ornamental or essential? 26 00:01:35,900 --> 00:01:38,960 At first the bird acts just as if the water were still there. 27 00:01:39,980 --> 00:01:43,660 Now let’s speed up the bird’s motion you see at 15 minutes it is still drinking. 28 00:01:43,960 --> 00:01:45,560 At 30 still drinking. 29 00:01:45,820 --> 00:01:47,640 45 minutes still drinking. 30 00:01:47,880 --> 00:01:49,760 60 minutes still drinking. 31 00:01:49,920 --> 00:01:51,920 75 minutes still drinking. 32 00:01:52,300 --> 00:01:57,100 And five or ten minutes later, at eighty or eight-five minutes it takes its last drink. 33 00:01:57,540 --> 00:02:02,580 The liquid still rises a bit, but it never rises enough to make the bird tip over, which 34 00:02:02,580 --> 00:02:08,130 shows that the motion is not perpetual — as long as there is water, the bird keeps drinking. 35 00:02:08,130 --> 00:02:11,510 Let’s look inside the bird to get an idea of how it works. 36 00:02:11,510 --> 00:02:16,060 Underneath the bird’s hat, beak and fabric covering lies a glass bulb, smaller than the 37 00:02:16,060 --> 00:02:18,060 bulb at the base, and also rounder. 38 00:02:18,780 --> 00:02:23,940 Now, watch as I put a few drops of isopropyl alcohol on the top bulb to cool it. 39 00:02:24,640 --> 00:02:29,360 The liquid rapidly rises to the head, this changes the bird’s center of gravity so 40 00:02:29,359 --> 00:02:31,099 that it will tilt forward. 41 00:02:31,100 --> 00:02:33,460 The head now fills with liquid and then … 42 00:02:34,960 --> 00:02:35,520 there ... 43 00:02:40,020 --> 00:02:41,200 … it … drinks. 44 00:02:41,300 --> 00:02:46,680 It becomes upright and the liquid drains from the head … liquid rises again to the head and ... 45 00:02:50,000 --> 00:02:51,620 the bird drinks again. 46 00:02:52,660 --> 00:02:56,180 This cycle repeats until all of the isopropyl alcohol 47 00:02:56,180 --> 00:02:57,940 on the bird’s heat evaporates. 48 00:02:58,410 --> 00:03:00,540 Why does the liquid rise? 49 00:03:00,540 --> 00:03:04,230 The place to begin is with the bird’s manufacture. 50 00:03:04,230 --> 00:03:07,810 The bird is filled through this “tap” — a small pipe built into the head — with 51 00:03:07,810 --> 00:03:13,430 methylene chloride dyed red, which is then frozen, a vacuum applied to evacuate the air, 52 00:03:13,430 --> 00:03:16,420 the tap sealed (and, of course, later hidden by the bird’s hat) . . . 53 00:03:16,860 --> 00:03:19,080 And then the methylene chloride melts: 54 00:03:19,080 --> 00:03:23,320 It turns to liquid and then some of it evaporates (turns into vapor). 55 00:03:23,319 --> 00:03:27,369 The key to the bird’s operation is that the vapor in the head and in the base are 56 00:03:27,370 --> 00:03:29,030 separated by the liquid in the base. 57 00:03:29,030 --> 00:03:34,350 It’s hard to see, but the tube extends into the base, nearly reaching the bottom. 58 00:03:34,349 --> 00:03:38,579 This separates the vapor in base and the vapor in the tube and …. 59 00:03:39,060 --> 00:03:40,440 of course, the head. 60 00:03:40,620 --> 00:03:45,340 So, at rest the pressure in these two spaces are equal, but when the bird’s beak is wet, 61 00:03:45,340 --> 00:03:49,380 the temperature falls and, as I’ll explain in a moment, the pressure in the head drops 62 00:03:49,380 --> 00:03:52,120 below that in the base and the liquid rises. 63 00:03:53,820 --> 00:03:57,060 Of course this liquid in the head causes the bird to . . . 64 00:03:57,480 --> 00:03:58,840 tilt forward, to drink … 65 00:03:59,160 --> 00:04:03,760 and when it drinks, the vapor in the head and the base are connected, the pressures nearly 66 00:04:03,760 --> 00:04:08,740 equalize — a slug of vapor rises to the top and some liquid drains from the head and 67 00:04:08,739 --> 00:04:10,449 and then the cycle repeats. 68 00:04:10,450 --> 00:04:14,220 To see the pressure equalize I’ll slow down the bird as I tilt it forward. 69 00:04:14,219 --> 00:04:16,269 Right now the head is half full. 70 00:04:16,269 --> 00:04:19,499 When I tilt it you see a slug of vapor go from bottom to top. 71 00:04:19,500 --> 00:04:23,530 I’ve titled it far enough forward that the liquid in the head is below the top of the 72 00:04:23,530 --> 00:04:27,810 tube and the liquid in the base is below the section of the tube that almost reaches the 73 00:04:27,810 --> 00:04:29,440 bottom of the bird. 74 00:04:29,440 --> 00:04:33,760 This allows the pressure to equalize, and as the bird becomes upright the liquid returns 75 00:04:33,760 --> 00:04:36,170 to the base before the cycle starts again. 76 00:04:36,170 --> 00:04:41,620 In operation it doesn’t tilt quite this far forward and so the pressures don’t fully equalize. 77 00:04:41,620 --> 00:04:45,660 Why, though, does the pressure in the head drop as the temperature falls? 78 00:04:45,660 --> 00:04:50,560 You can see the answer if I shoot cool, compressed gas across the bird’s head. 79 00:04:50,560 --> 00:04:56,220 As the cool gas strikes, you see liquid condensing inside the head; and , as you see on the left, 80 00:04:56,220 --> 00:04:58,940 this causes the liquid in the base to rise. 81 00:04:58,940 --> 00:05:03,150 The cool gas withdraws energy as heat from the head causing some of the methylene chloride 82 00:05:03,150 --> 00:05:08,370 vapor inside to condense - to turn into a liquid — this decreases dramatically the 83 00:05:08,370 --> 00:05:13,100 amount of vapor in the head — liquid is 1,000 times more dense than vapor — this 84 00:05:13,100 --> 00:05:16,940 in turn lowers the pressure in the head and causes the liquid to rise. 85 00:05:16,940 --> 00:05:22,430 I used compressed gas to cool the head because I can control the amount of cooling; the bird, 86 00:05:22,430 --> 00:05:24,940 though, cools its head by “drinking.” 87 00:05:24,940 --> 00:05:27,800 The head is wrapped in fabric that absorbs water. 88 00:05:27,800 --> 00:05:31,300 As I put drops on its beak you can see the water beads up at first . . . 89 00:05:31,300 --> 00:05:35,580 then saturates the fabric and spreads rapidly across the bird’s face. 90 00:05:35,590 --> 00:05:38,830 On the right side you can see it creeping to back of the head. 91 00:05:38,830 --> 00:05:43,640 If I now turn the bird around … you can see that the water has spread to the back. 92 00:05:43,640 --> 00:05:48,490 As I continue adding drops on the beak the saturated area on the back increases. 93 00:05:48,490 --> 00:05:52,620 When this water evaporates into the air it removes energy from the bulb as heat — 94 00:05:52,620 --> 00:05:57,260 you feel this effect every time you step out of the shower, the evaporating water withdraws 95 00:05:57,260 --> 00:05:59,640 energy as heat and chills you. 96 00:05:59,640 --> 00:06:04,700 This evaporation, this withdrawal of heat, lowers the temperature and begins the condensation 97 00:06:04,700 --> 00:06:09,440 of the vapor, which starts the cycle as I showed you with the cool, compressed gas. 98 00:06:09,440 --> 00:06:13,880 As long as the head is wet and heat is withdrawn from it, the bird will always “drink,” 99 00:06:13,880 --> 00:06:17,920 but if you were to operate the bird in humid air it would slow down because little water 100 00:06:17,920 --> 00:06:23,980 would evaporate, and if the air were at 100% humidity the bird would stop because no water 101 00:06:23,980 --> 00:06:25,910 would evaporate at all. 102 00:06:25,910 --> 00:06:30,430 Now, to make this dramatic condensation happen when the temperature is lowered just slightly 103 00:06:30,430 --> 00:06:35,500 — the evaporating water lowers the temperature by only about three-tenths of a degree — the 104 00:06:35,500 --> 00:06:38,660 bird’s designer choose a highly volatile liquid. 105 00:06:38,660 --> 00:06:42,570 This means one whose boiling point is near ambient temperature because for small changes 106 00:06:42,570 --> 00:06:47,150 in temperature there is a large change from vapor to liquid and so the variation of pressure 107 00:06:47,150 --> 00:06:48,550 is large. 108 00:06:48,550 --> 00:06:52,100 Watch what happens as I “heat” the base of the bird with my hand. 109 00:06:52,100 --> 00:06:56,310 You see the liquid level in the base dropping: that’s because energy from my hand is converting 110 00:06:56,310 --> 00:07:00,600 some of the liquid into vapor, which increases the pressure in this region . . . 111 00:07:00,600 --> 00:07:04,500 and that causes the liquid to rise to the head. 112 00:07:10,960 --> 00:07:13,400 Eventually I heat the vapor so much 113 00:07:13,400 --> 00:07:14,800 that it shoots up the stem. 114 00:07:15,300 --> 00:07:18,460 Now watch as I place my hand around the head. 115 00:07:18,460 --> 00:07:22,650 Heat from my hand converts liquid to vapor, which increases the pressure and forces the 116 00:07:22,650 --> 00:07:24,400 liquid back to the base. 117 00:07:25,320 --> 00:07:30,560 To test this explanation of the bird’s operation, let’s activate the bird in different ways. 118 00:07:30,560 --> 00:07:34,410 As I noted it is the temperature difference between its top and bottom that drives liquid 119 00:07:34,410 --> 00:07:35,460 to rise to the head. 120 00:07:35,460 --> 00:07:40,280 So, let’s see what happens if I point a light at the base of the bird, which 121 00:07:41,820 --> 00:07:44,880 I’ve painted black so it will absorb the energy from the light better. 122 00:07:44,880 --> 00:07:48,980 As I heat the base of the bird, the liquid rises, as before but … 123 00:07:55,360 --> 00:07:57,500 the bird tips backwards. 124 00:07:57,500 --> 00:08:01,780 The wet nose tilted the center of gravity … and so I added some modelling clay to 125 00:08:01,780 --> 00:08:04,010 the nose to get the bird to tilt forward. 126 00:08:04,010 --> 00:08:08,590 And now when I turn on the light the liquid rises, the birds drinks just as if there were 127 00:08:08,590 --> 00:08:10,380 liquid in front of it until . . . 128 00:08:13,700 --> 00:08:14,980 I turn the light off … 129 00:08:15,360 --> 00:08:17,460 and the bird drinks for a little bit longer 130 00:08:17,460 --> 00:08:18,060 until eventually . . . 131 00:08:19,040 --> 00:08:20,300 it comes to rest. 132 00:08:20,380 --> 00:08:24,360 Next, let’s see what happens if we use this: Whiskey. 133 00:08:24,780 --> 00:08:27,720 Again, thoroughly wet the bird’s beak with the liquid . . . 134 00:08:31,740 --> 00:08:36,440 stand it upright … and then we see again the liquid rising in the bird 135 00:08:37,400 --> 00:08:38,080 . . . and then 136 00:08:38,360 --> 00:08:39,400 … it drinks. 137 00:08:40,000 --> 00:08:44,540 We can also now understand why the bird’s rate of drinking differs among the three methods 138 00:08:44,540 --> 00:08:49,310 I used to “activate” the bird: a heat lamp, whiskey and water. 139 00:08:49,310 --> 00:08:53,080 Roughly, the heat bird takes three drinks for every one of the water bird, 140 00:08:53,580 --> 00:08:57,400 the whiskey bird takes two for every drink of the water bird. 141 00:08:57,399 --> 00:09:02,269 The reason the bird drinks whiskey faster than water is because the rate of evaporation 142 00:09:02,269 --> 00:09:05,009 of the alcohol is greater than that of water. 143 00:09:05,009 --> 00:09:09,189 This means that heat is withdrawn faster from the head and so more vapor condenses in a 144 00:09:09,189 --> 00:09:12,739 shorter amount of time, which accelerates the pressure difference. 145 00:09:13,080 --> 00:09:17,460 The heat lamp causes the greatest difference of all, which highlights how an engineer thinks 146 00:09:17,470 --> 00:09:19,020 about this bird. 147 00:09:19,019 --> 00:09:21,249 To an engineer this bird is a heat engine. 148 00:09:21,249 --> 00:09:25,269 A heat engine turns heat differences into work — mechanical motion. 149 00:09:25,270 --> 00:09:28,940 To see that recall that when the bird is just about to drink that its head is at a lower 150 00:09:28,939 --> 00:09:32,779 temperature than its base, which is at ambient temperature. 151 00:09:32,779 --> 00:09:36,809 Then when it “drinks” the pressure in the head and base start to equalize so liquid 152 00:09:36,810 --> 00:09:40,420 returns to the base, but the overall temperature of the bird is now 153 00:09:40,420 --> 00:09:42,460 just a little below ambient temperature. 154 00:09:42,470 --> 00:09:47,390 When it return to upright the base draws in energy as heat . . . the head then rejects 155 00:09:47,390 --> 00:09:50,550 some energy as heat and the bird drinks again. 156 00:09:50,550 --> 00:09:56,110 These two flows define a heat engine: a device, operating in a cycle that absorbs heat from 157 00:09:56,110 --> 00:10:00,830 a high temperature reservoir, converts part of it into work, and rejects the remainder 158 00:10:00,829 --> 00:10:03,249 into a low temperature reservoir. 159 00:10:03,249 --> 00:10:06,739 The fact that this is a heat engine means it’s related to the great machines that 160 00:10:06,740 --> 00:10:12,050 make our globalized world happen: among those the mighty steam turbine that generates electricity, 161 00:10:12,050 --> 00:10:17,690 the giant diesel engine that propels container ships across the oceans, and the great gas 162 00:10:17,690 --> 00:10:19,860 turbine that flies us around the globe. 163 00:10:20,180 --> 00:10:22,440 I’m Bill Hammack, the engineer guy.