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Electrical Charges

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Why? Files segment exploring lightning and the different types of electrical charges.

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Hi, Dr. D. 00:00:00
Hi. 00:00:02
Hi, guys. 00:00:03
Can you tell us what lightning is? 00:00:04
Sure. Wait a minute, what brings this up? 00:00:06
Well, I was telling Kaylee and Jacob that the power is still out across the street, 00:00:08
but it's still on in our treehouse. 00:00:12
We're trying to figure out why. 00:00:14
Where are you going to start? 00:00:16
We came up with a hypothesis. 00:00:17
We think that lightning caused the power outage. 00:00:18
It was a pretty big storm last night. 00:00:20
How are you going to test your hypothesis? 00:00:22
We're not sure. 00:00:24
Well, to understand lightning, we first need to look at some basics. 00:00:25
Let's rip up this paper. 00:00:30
Now, comb your hair briskly and then bring the comb down close to the paper. 00:00:32
Neat. 00:00:42
Why did it do that? 00:00:43
The ancient Greeks noticed the same thing when they rubbed amber with wool. 00:00:45
Who's amber? 00:00:48
Not who, but what. Amber is fossilized tree sap. 00:00:50
Oh, okay. 00:00:53
The amber picked up little objects like strands of fiber and hair, 00:00:55
just like the comb picked up the paper. 00:00:58
We say that the comb and the amber are electrically charged. 00:01:00
Can other objects do the same thing? 00:01:03
Sure. This balloon can pick up the paper, too. 00:01:06
And it picks up other things, too, 00:01:16
like this rice cereal and salt. 00:01:19
The balloon will also stick to the wall. 00:01:23
It can also attract the stream of water. 00:01:29
Whoa! 00:01:33
If you rub the acrylic rod with a plastic bag, it'll do the same thing. 00:01:36
Now, how do you know that the balloon was charged and not the paper? 00:01:40
Well, if an object is electrically charged, 00:01:43
it should pick up objects like little pieces of paper or other such objects. 00:01:46
Let's see. 00:01:50
Nothing happened. 00:01:54
Very good. 00:01:55
A charged object will pick up other neutral and uncharged objects, 00:01:56
but an uncharged object won't. 00:01:59
Let's do an experiment with some tape. 00:02:01
Bring this bar around. 00:02:03
Put some tape on the table. 00:02:10
I'll pull it up real quickly. 00:02:12
And watch this. 00:02:15
It attracted the paper. 00:02:21
It must be charged. 00:02:23
Now let's try two pieces of tape, one on top of each other. 00:02:24
Hold on to that, please. 00:02:34
How can we tell if these are charged? 00:02:35
We need to do the paper scraps test to find out. 00:02:37
Let's try it. 00:02:40
Yep, they're charged all right. 00:02:42
Well, here's the experiment. 00:02:45
Let's hang up the single piece of charged tape. 00:02:48
Now we'll pull up the double tape. 00:02:52
Rehearse the top piece. 00:02:55
It attracts the tape, just like before. 00:02:58
It's repelling the second tape. 00:03:02
We haven't seen that before. 00:03:04
What conclusions can you make? 00:03:05
Well, if an object is charged, it attracts uncharged items, 00:03:07
but it may attract or repel other charged items. 00:03:11
Does that mean there are two types of charges? 00:03:14
That's right. 00:03:17
Two types of charges are positive and negative. 00:03:18
The top piece and the bottom piece have different charges. 00:03:20
Now let's do this again. 00:03:23
This time we'll take both pieces of tape in exactly the same way. 00:03:25
So... 00:03:30
They must have the same charge. 00:03:33
That's right. 00:03:35
Will they attract or repel? 00:03:37
They repel. 00:03:42
Let's see. 00:03:44
If the charges are different, then they must attract. 00:03:45
Let's find out. 00:03:48
All right, we used the two tapes again. 00:03:49
Both have different charges. 00:03:52
How about that? 00:03:56
Look at this machine. 00:04:00
It's called a Van de Graaff generator. 00:04:01
Jacob, stand up on this stool, if you would, 00:04:03
and put your hands on top. 00:04:05
I'm going to turn this machine on and transfer a lot of charge into you. 00:04:08
It won't shock you, I promise. 00:04:12
Wow, his hair is really standing out. 00:04:15
Is it because all my hair is charged the same way 00:04:22
and each strand is repelling or pushing away from the strand next to it? 00:04:25
That's right. 00:04:29
In the beginning, your body was neutral. 00:04:30
It had the same number of positive and negative charges. 00:04:32
All the positive charges, protons, 00:04:34
and negative charges, electrons. 00:04:36
When we transfer an awful lot of negatively charged electrons 00:04:38
into your body, what kind of charge would you have then? 00:04:41
Well, if the number of electrons and protons in his body were the same, 00:04:44
then they would basically cancel each other out. 00:04:49
And then if we added a lot of electrons, 00:04:51
then I guess his body would be negatively charged. 00:04:53
That's right. 00:04:57
And I always thought you were the negative one. 00:04:58
Now, if we turn the thing on again, 00:05:00
build up a huge charge on top, 00:05:03
move the second ball closer to the first, 00:05:05
Wow, it looks just like lightning. 00:05:08
Now, what's going on there? 00:05:13
Well, the electrons are jumping from the Van de Graaff to the ball. 00:05:15
It looks more like a flash of light than a bunch of particles. 00:05:19
Well, I learned that you can't see electrons, 00:05:22
so how can we see these electrons? 00:05:25
Well, you're right. 00:05:27
Electrons aren't too small to see. 00:05:28
But as the electrons jump from the Van de Graaff to the ball, 00:05:30
That's right. Electrons aren't too small to see. 00:05:33
But as the electrons jump from the Van de Graaff to the ball, 00:05:35
they heat up the air and cause it to glow. 00:05:38
What you're seeing is the glowing air, not the moving electrons. 00:05:40
Is this how lightning works? 00:05:43
Yes, it's very similar. 00:05:44
So, Dr. D., did we get electricity from lightning? 00:05:46
Not quite. I'll tell you what. 00:05:49
I'm going to line you up with a researcher 00:05:51
at the NASA Langley Research Center in Hampton, Virginia. 00:05:53
His name is Bruce Fisher. 00:05:55
He's done a lot of studies on lightning. 00:05:57
I'll arrange for you to meet him at the Virginia Air and Space Center. 00:05:59
Great! Thanks, Dr. D. 00:06:01
So, let's get up and go. 00:06:03
Bye, Dr. D. 00:06:05
Bye, guys. 00:06:06
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Idioma/s:
en
Niveles educativos:
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Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
460
Fecha:
28 de mayo de 2007 - 15:34
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
06′ 07″
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:
36.84 MBytes

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