1 00:00:00,000 --> 00:00:02,000 Good morning, Mrs. Rickles. 2 00:00:02,000 --> 00:00:03,000 Well, good morning. 3 00:00:03,000 --> 00:00:05,000 I've got your e-mail this morning, 4 00:00:05,000 --> 00:00:06,000 and I have just the experiment for you. 5 00:00:06,000 --> 00:00:08,000 I have it all written down here. 6 00:00:08,000 --> 00:00:09,000 Here you go. 7 00:00:09,000 --> 00:00:10,000 Thanks, Mrs. Rickles, for helping us. 8 00:00:10,000 --> 00:00:11,000 You're welcome. 9 00:00:11,000 --> 00:00:14,000 It looks like we need to go outside and create echoes. 10 00:00:14,000 --> 00:00:16,000 And measure how long it takes us to hear those echoes. 11 00:00:16,000 --> 00:00:17,000 Let's get started. 12 00:00:17,000 --> 00:00:19,000 Okay. 13 00:00:19,000 --> 00:00:22,000 Okay, everybody line up in threes. 14 00:00:22,000 --> 00:00:24,000 One person will do the clapping, 15 00:00:24,000 --> 00:00:26,000 the other person will time the number of claps, 16 00:00:26,000 --> 00:00:28,000 and the other will take the data. 17 00:00:28,000 --> 00:00:31,000 You need a set of pipes, a meter stick, 18 00:00:31,000 --> 00:00:34,000 a stopwatch, a pencil and a paper, and goggles. 19 00:00:34,000 --> 00:00:37,000 We will use the side of the building to bounce sounds off 20 00:00:37,000 --> 00:00:38,000 to create an echo. 21 00:00:38,000 --> 00:00:41,000 Measure 57 meters from that wall. 22 00:00:41,000 --> 00:00:43,000 I can do that, but I need help. 23 00:00:43,000 --> 00:00:45,000 Help! 24 00:00:53,000 --> 00:00:55,000 Okay, you need to stand right here. 25 00:00:55,000 --> 00:00:57,000 This is where we'll start the experiment. 26 00:00:57,000 --> 00:01:00,000 We need to start clapping these two items together like this 27 00:01:00,000 --> 00:01:02,000 and listen for the echo. 28 00:01:02,000 --> 00:01:04,000 You really need to get a rhythm going 29 00:01:04,000 --> 00:01:07,000 so that you can hear the echo in between claps like this. 30 00:01:08,000 --> 00:01:10,000 Let's try it. 31 00:01:10,000 --> 00:01:12,000 That's good. 32 00:01:12,000 --> 00:01:14,000 Okay, I'm hearing the echo. 33 00:01:14,000 --> 00:01:16,000 Let's time the number of claps in 20 seconds 34 00:01:16,000 --> 00:01:18,000 and report our data so we can analyze it 35 00:01:18,000 --> 00:01:20,000 when we get back inside. 36 00:01:23,000 --> 00:01:24,000 I have 30 claps. 37 00:01:24,000 --> 00:01:25,000 That's great. 38 00:01:25,000 --> 00:01:27,000 Let's do the experiment again 39 00:01:27,000 --> 00:01:29,000 so we can take an average of the number of claps. 40 00:01:29,000 --> 00:01:31,000 Remember, when you are experimenting, 41 00:01:31,000 --> 00:01:33,000 you must have repeated trials. 42 00:01:33,000 --> 00:01:36,000 In the stink problem, we learned that we need to perform 43 00:01:36,000 --> 00:01:38,000 the experiment at least three times. 44 00:01:38,000 --> 00:01:41,000 Okay, we need another group to line up. 45 00:01:41,000 --> 00:01:42,000 Let's count down. 46 00:01:42,000 --> 00:01:46,000 Three, two, one, go! 47 00:01:56,000 --> 00:01:59,000 Do you know why it's important to take an average? 48 00:01:59,000 --> 00:02:02,000 Taking an average helps us to eliminate the possibility 49 00:02:02,000 --> 00:02:04,000 that someone counted wrong, 50 00:02:04,000 --> 00:02:06,000 read the stopwatch wrong, 51 00:02:06,000 --> 00:02:08,000 or didn't understand the instructions. 52 00:02:08,000 --> 00:02:10,000 Do you know how to calculate an average? 53 00:02:10,000 --> 00:02:12,000 It's easy. 54 00:02:12,000 --> 00:02:16,000 For example, you can take the numbers 20, 22, and 19. 55 00:02:16,000 --> 00:02:18,000 You add them up and divide them by 3, 56 00:02:18,000 --> 00:02:20,000 and that's your average. 57 00:02:20,000 --> 00:02:22,000 Now to calculate the speed of sound, 58 00:02:23,000 --> 00:02:25,000 Now to calculate the speed of sound, 59 00:02:25,000 --> 00:02:27,000 we need to take the number of seconds 60 00:02:27,000 --> 00:02:30,000 and we need to divide it by the number of claps. 61 00:02:30,000 --> 00:02:33,000 This is going to tell us the amount of time between claps. 62 00:02:33,000 --> 00:02:35,000 What do we get? 63 00:02:35,000 --> 00:02:37,000 That's 0.66. 64 00:02:37,000 --> 00:02:40,000 Let's see, I calculate that to be 65 00:02:40,000 --> 00:02:43,000 two-thirds of a second between claps. 66 00:02:43,000 --> 00:02:47,000 Okay, we have two-thirds of a second between claps, 67 00:02:47,000 --> 00:02:50,000 and the echo comes halfway between claps. 68 00:02:50,000 --> 00:02:52,000 Then it only takes one-third of a second 69 00:02:52,000 --> 00:02:55,000 for the sound to travel to the wall and back to us. 70 00:02:55,000 --> 00:02:57,000 I guess that sounds correct. 71 00:02:57,000 --> 00:02:59,000 And to figure out how far it travels 72 00:02:59,000 --> 00:03:01,000 from us to the wall and back, 73 00:03:01,000 --> 00:03:04,000 wouldn't we just take 57 meters and double it? 74 00:03:04,000 --> 00:03:07,000 What, 114 meters? 75 00:03:07,000 --> 00:03:08,000 Correct. 76 00:03:08,000 --> 00:03:10,000 Now to figure out the speed, 77 00:03:10,000 --> 00:03:12,000 divide distance traveled by the time. 78 00:03:12,000 --> 00:03:15,000 Okay, that would be 114 meters 79 00:03:15,000 --> 00:03:17,000 divided by one-third of a second. 80 00:03:17,000 --> 00:03:20,000 That comes to 342 meters per second. 81 00:03:20,000 --> 00:03:22,000 That's beyond fast. 82 00:03:22,000 --> 00:03:25,000 A meter is just a little longer than a yard. 83 00:03:25,000 --> 00:03:27,000 This means that sound travels 84 00:03:27,000 --> 00:03:29,000 more than three football fields in a second. 85 00:03:29,000 --> 00:03:32,000 Wow, that's really fast. 86 00:03:32,000 --> 00:03:35,000 Now we actually saw how fast sound travels. 87 00:03:35,000 --> 00:03:37,000 Let's go tell Dr. D. 88 00:03:37,000 --> 00:03:39,000 Hey, Dr. D. 89 00:03:39,000 --> 00:03:41,000 Oh, hi, kids. 90 00:03:41,000 --> 00:03:44,000 Dr. D, I did this really cool experiment at school 91 00:03:44,000 --> 00:03:47,000 and it showed that sound traveled so fast. 92 00:03:47,000 --> 00:03:50,000 What do you think affects how fast sound travels? 93 00:03:50,000 --> 00:03:52,000 Oh, you mean, what are the variables? 94 00:03:52,000 --> 00:03:53,000 Ah, very good. 95 00:03:53,000 --> 00:03:55,000 Could it have anything to do with the temperature? 96 00:03:55,000 --> 00:03:57,000 That's a great question. 97 00:03:57,000 --> 00:03:59,000 The speed of sound increases with temperature. 98 00:03:59,000 --> 00:04:00,000 That's one variable. 99 00:04:00,000 --> 00:04:02,000 Another variable is the moisture. 100 00:04:02,000 --> 00:04:04,000 I guess this means that on hot, humid days, 101 00:04:04,000 --> 00:04:06,000 when it's really sticky outside, 102 00:04:06,000 --> 00:04:08,000 the sound travels really fast. 103 00:04:08,000 --> 00:04:09,000 No, not that much faster. 104 00:04:09,000 --> 00:04:11,000 The material that sound travels through, 105 00:04:11,000 --> 00:04:13,000 which we call the medium, makes a big difference. 106 00:04:13,000 --> 00:04:15,000 Generally, sound travels faster through liquids 107 00:04:15,000 --> 00:04:16,000 than they do through air. 108 00:04:16,000 --> 00:04:19,000 They travel faster through solids than through liquids. 109 00:04:19,000 --> 00:04:20,000 Why does that happen? 110 00:04:20,000 --> 00:04:21,000 It's called elasticity. 111 00:04:21,000 --> 00:04:23,000 I'll show you how it works. 112 00:04:23,000 --> 00:04:24,000 I'm doing an experiment. 113 00:04:24,000 --> 00:04:26,000 Matthew, why don't you finish lining up the dominoes 114 00:04:26,000 --> 00:04:27,000 on the table, if you would, please. 115 00:04:27,000 --> 00:04:28,000 Sure. 116 00:04:30,000 --> 00:04:32,000 Bianca, grab a hold of this spring 117 00:04:32,000 --> 00:04:34,000 and hold on really tight. 118 00:04:34,000 --> 00:04:37,000 I'm going to send a wave pulse down the spring. 119 00:04:37,000 --> 00:04:39,000 Pay careful attention to how fast it's going. 120 00:04:40,000 --> 00:04:41,000 All right. 121 00:04:41,000 --> 00:04:44,000 Now, solids and liquids are more elastic than gases. 122 00:04:44,000 --> 00:04:46,000 See how much of a difference this makes? 123 00:04:46,000 --> 00:04:49,000 I'm going to increase the elasticity of this spring 124 00:04:49,000 --> 00:04:51,000 by increasing its tension. 125 00:04:51,000 --> 00:04:54,000 Elasticity tells me how fast things are brought back 126 00:04:54,000 --> 00:04:56,000 into place when they're disturbed. 127 00:04:56,000 --> 00:04:57,000 Are you ready? 128 00:04:57,000 --> 00:04:58,000 Watch carefully. 129 00:05:01,000 --> 00:05:02,000 Wow, it's really moving. 130 00:05:02,000 --> 00:05:05,000 Notice how the wave or energy travels through the spring, 131 00:05:05,000 --> 00:05:07,000 but the spring doesn't go anywhere. 132 00:05:07,000 --> 00:05:09,000 It just vibrates in place. 133 00:05:09,000 --> 00:05:11,000 It's like the dominoes that Matthew just set up. 134 00:05:11,000 --> 00:05:13,000 When he knocks over the first one, 135 00:05:13,000 --> 00:05:15,000 the energy will travel through, 136 00:05:15,000 --> 00:05:18,000 but the individual dominoes just move a little bit. 137 00:05:18,000 --> 00:05:19,000 Try it, Matthew. 138 00:05:19,000 --> 00:05:20,000 Okay. 139 00:05:26,000 --> 00:05:27,000 Cool. 140 00:05:27,000 --> 00:05:28,000 Now we know that sound gets softer 141 00:05:28,000 --> 00:05:30,000 as it travels away from a source. 142 00:05:30,000 --> 00:05:31,000 When sound travels from medium, 143 00:05:31,000 --> 00:05:33,000 the molecules vibrate in place, 144 00:05:33,000 --> 00:05:34,000 but don't really go anywhere. 145 00:05:34,000 --> 00:05:36,000 What else do we know about sound? 146 00:05:36,000 --> 00:05:39,000 Well, we know the medium affects how fast sound travels. 147 00:05:39,000 --> 00:05:42,000 We also know it influences how far sound goes. 148 00:05:42,000 --> 00:05:44,000 But I thought we already talked about 149 00:05:44,000 --> 00:05:46,000 how sound died off in the distance 150 00:05:46,000 --> 00:05:48,000 when we were in that room with all the sponges. 151 00:05:48,000 --> 00:05:49,000 Well, that's right. 152 00:05:49,000 --> 00:05:51,000 We discussed how sound gets softer with distance 153 00:05:51,000 --> 00:05:53,000 because the waves spread out. 154 00:05:53,000 --> 00:05:55,000 Is that like when you throw a rock into a pond of water 155 00:05:55,000 --> 00:05:58,000 and the circles get bigger as they move away from the splash? 156 00:05:58,000 --> 00:05:59,000 Exactly. 157 00:05:59,000 --> 00:06:00,000 But in addition to that, 158 00:06:00,000 --> 00:06:03,000 the medium affects how far sound travels 159 00:06:03,000 --> 00:06:05,000 by absorbing the sound energy. 160 00:06:05,000 --> 00:06:08,000 I have a friend over at NASA who specializes in acoustics. 161 00:06:08,000 --> 00:06:10,000 Her name is Dr. Christine Darden. 162 00:06:10,000 --> 00:06:11,000 She'd go talk with her. 163 00:06:11,000 --> 00:06:12,000 She can help you to understand 164 00:06:12,000 --> 00:06:15,000 how the medium affects how far sound travels. 165 00:06:15,000 --> 00:06:18,000 Maybe we can dial her up when we get back to the treehouse. 166 00:06:18,000 --> 00:06:20,000 Thanks for all your help, Dr. D. 167 00:06:20,000 --> 00:06:21,000 See ya. 168 00:06:21,000 --> 00:06:22,000 Bye. 169 00:06:22,000 --> 00:06:23,000 Bye, guys.