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Sound Over Distance

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Why? Files segment exploring how sound travels and the speed of sound through classroom activities.

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Good morning, Mrs. Rickles. 00:00:00
Well, good morning. 00:00:02
I've got your e-mail this morning, 00:00:03
and I have just the experiment for you. 00:00:05
I have it all written down here. 00:00:06
Here you go. 00:00:08
Thanks, Mrs. Rickles, for helping us. 00:00:09
You're welcome. 00:00:10
It looks like we need to go outside and create echoes. 00:00:11
And measure how long it takes us to hear those echoes. 00:00:14
Let's get started. 00:00:16
Okay. 00:00:17
Okay, everybody line up in threes. 00:00:19
One person will do the clapping, 00:00:22
the other person will time the number of claps, 00:00:24
and the other will take the data. 00:00:26
You need a set of pipes, a meter stick, 00:00:28
a stopwatch, a pencil and a paper, and goggles. 00:00:31
We will use the side of the building to bounce sounds off 00:00:34
to create an echo. 00:00:37
Measure 57 meters from that wall. 00:00:38
I can do that, but I need help. 00:00:41
Help! 00:00:43
Okay, you need to stand right here. 00:00:53
This is where we'll start the experiment. 00:00:55
We need to start clapping these two items together like this 00:00:57
and listen for the echo. 00:01:00
You really need to get a rhythm going 00:01:02
so that you can hear the echo in between claps like this. 00:01:04
Let's try it. 00:01:08
That's good. 00:01:10
Okay, I'm hearing the echo. 00:01:12
Let's time the number of claps in 20 seconds 00:01:14
and report our data so we can analyze it 00:01:16
when we get back inside. 00:01:18
I have 30 claps. 00:01:23
That's great. 00:01:24
Let's do the experiment again 00:01:25
so we can take an average of the number of claps. 00:01:27
Remember, when you are experimenting, 00:01:29
you must have repeated trials. 00:01:31
In the stink problem, we learned that we need to perform 00:01:33
the experiment at least three times. 00:01:36
Okay, we need another group to line up. 00:01:38
Let's count down. 00:01:41
Three, two, one, go! 00:01:42
Do you know why it's important to take an average? 00:01:56
Taking an average helps us to eliminate the possibility 00:01:59
that someone counted wrong, 00:02:02
read the stopwatch wrong, 00:02:04
or didn't understand the instructions. 00:02:06
Do you know how to calculate an average? 00:02:08
It's easy. 00:02:10
For example, you can take the numbers 20, 22, and 19. 00:02:12
You add them up and divide them by 3, 00:02:16
and that's your average. 00:02:18
Now to calculate the speed of sound, 00:02:20
Now to calculate the speed of sound, 00:02:23
we need to take the number of seconds 00:02:25
and we need to divide it by the number of claps. 00:02:27
This is going to tell us the amount of time between claps. 00:02:30
What do we get? 00:02:33
That's 0.66. 00:02:35
Let's see, I calculate that to be 00:02:37
two-thirds of a second between claps. 00:02:40
Okay, we have two-thirds of a second between claps, 00:02:43
and the echo comes halfway between claps. 00:02:47
Then it only takes one-third of a second 00:02:50
for the sound to travel to the wall and back to us. 00:02:52
I guess that sounds correct. 00:02:55
And to figure out how far it travels 00:02:57
from us to the wall and back, 00:02:59
wouldn't we just take 57 meters and double it? 00:03:01
What, 114 meters? 00:03:04
Correct. 00:03:07
Now to figure out the speed, 00:03:08
divide distance traveled by the time. 00:03:10
Okay, that would be 114 meters 00:03:12
divided by one-third of a second. 00:03:15
That comes to 342 meters per second. 00:03:17
That's beyond fast. 00:03:20
A meter is just a little longer than a yard. 00:03:22
This means that sound travels 00:03:25
more than three football fields in a second. 00:03:27
Wow, that's really fast. 00:03:29
Now we actually saw how fast sound travels. 00:03:32
Let's go tell Dr. D. 00:03:35
Hey, Dr. D. 00:03:37
Oh, hi, kids. 00:03:39
Dr. D, I did this really cool experiment at school 00:03:41
and it showed that sound traveled so fast. 00:03:44
What do you think affects how fast sound travels? 00:03:47
Oh, you mean, what are the variables? 00:03:50
Ah, very good. 00:03:52
Could it have anything to do with the temperature? 00:03:53
That's a great question. 00:03:55
The speed of sound increases with temperature. 00:03:57
That's one variable. 00:03:59
Another variable is the moisture. 00:04:00
I guess this means that on hot, humid days, 00:04:02
when it's really sticky outside, 00:04:04
the sound travels really fast. 00:04:06
No, not that much faster. 00:04:08
The material that sound travels through, 00:04:09
which we call the medium, makes a big difference. 00:04:11
Generally, sound travels faster through liquids 00:04:13
than they do through air. 00:04:15
They travel faster through solids than through liquids. 00:04:16
Why does that happen? 00:04:19
It's called elasticity. 00:04:20
I'll show you how it works. 00:04:21
I'm doing an experiment. 00:04:23
Matthew, why don't you finish lining up the dominoes 00:04:24
on the table, if you would, please. 00:04:26
Sure. 00:04:27
Bianca, grab a hold of this spring 00:04:30
and hold on really tight. 00:04:32
I'm going to send a wave pulse down the spring. 00:04:34
Pay careful attention to how fast it's going. 00:04:37
All right. 00:04:40
Now, solids and liquids are more elastic than gases. 00:04:41
See how much of a difference this makes? 00:04:44
I'm going to increase the elasticity of this spring 00:04:46
by increasing its tension. 00:04:49
Elasticity tells me how fast things are brought back 00:04:51
into place when they're disturbed. 00:04:54
Are you ready? 00:04:56
Watch carefully. 00:04:57
Wow, it's really moving. 00:05:01
Notice how the wave or energy travels through the spring, 00:05:02
but the spring doesn't go anywhere. 00:05:05
It just vibrates in place. 00:05:07
It's like the dominoes that Matthew just set up. 00:05:09
When he knocks over the first one, 00:05:11
the energy will travel through, 00:05:13
but the individual dominoes just move a little bit. 00:05:15
Try it, Matthew. 00:05:18
Okay. 00:05:19
Cool. 00:05:26
Now we know that sound gets softer 00:05:27
as it travels away from a source. 00:05:28
When sound travels from medium, 00:05:30
the molecules vibrate in place, 00:05:31
but don't really go anywhere. 00:05:33
What else do we know about sound? 00:05:34
Well, we know the medium affects how fast sound travels. 00:05:36
We also know it influences how far sound goes. 00:05:39
But I thought we already talked about 00:05:42
how sound died off in the distance 00:05:44
when we were in that room with all the sponges. 00:05:46
Well, that's right. 00:05:48
We discussed how sound gets softer with distance 00:05:49
because the waves spread out. 00:05:51
Is that like when you throw a rock into a pond of water 00:05:53
and the circles get bigger as they move away from the splash? 00:05:55
Exactly. 00:05:58
But in addition to that, 00:05:59
the medium affects how far sound travels 00:06:00
by absorbing the sound energy. 00:06:03
I have a friend over at NASA who specializes in acoustics. 00:06:05
Her name is Dr. Christine Darden. 00:06:08
She'd go talk with her. 00:06:10
She can help you to understand 00:06:11
how the medium affects how far sound travels. 00:06:12
Maybe we can dial her up when we get back to the treehouse. 00:06:15
Thanks for all your help, Dr. D. 00:06:18
See ya. 00:06:20
Bye. 00:06:21
Bye, guys. 00:06:22
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Idioma/s:
en
Niveles educativos:
▼ Mostrar / ocultar niveles
      • Nivel Intermedio
Autor/es:
Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
609
Fecha:
28 de mayo de 2007 - 15:32
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
06′ 22″
Relación de aspecto:
4:3 Hasta 2009 fue el estándar utilizado en la televisión PAL; muchas pantallas de ordenador y televisores usan este estándar, erróneamente llamado cuadrado, cuando en la realidad es rectangular o wide.
Resolución:
480x360 píxeles
Tamaño:
38.31 MBytes

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