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Launch Gravity - Contenido educativo

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Connect Segment explaining how launch vehicles overcome the force of gravity through the force of thrust.

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Hi, I'm Jennifer Pulley, your host, along with Dan Jarreau, who's joining us remotely 00:00:00
from the NASA Langley Research Center in Hampton, Virginia. 00:00:09
You know, we're real excited to be here at the U.S. Space and Rocket Center in Huntsville, 00:00:13
Alabama, for part of this NASA Connect. 00:00:16
Teachers, make sure you have the educator guide for today's program. 00:00:19
It can be downloaded from the NASA Connect website. 00:00:23
In it, you'll find great math-based, hands-on activities and information on our instructional 00:00:26
technology components. 00:00:32
On this episode of NASA Connect, we're visiting NASA Marshall Space Flight Center in Huntsville, 00:00:34
Alabama. 00:00:39
There, we'll meet NASA scientists and engineers who are exploring the challenges of building 00:00:40
the next generation of reusable spacecraft. 00:00:45
My friends here are going to help me figure out what it takes to get into orbit. 00:00:49
How can we do that? 00:00:52
By learning how NASA is getting spacecraft into orbit more safely and less expensively. 00:00:53
Can't we just keep doing it the way we always have? 00:00:58
Well, you know, things change, and we need to change in order to continue our journey 00:01:00
of exploration. 00:01:06
Just think, we went from the Wright brothers' first flight in 1903 to landing on the moon 00:01:07
in 1969. 00:01:14
As you can see, people have been dreaming of flight for ages. 00:01:16
One of those dreamers was American Robert Goddard, an early experimenter with rockets. 00:01:20
His work continues to inspire generations of scientists. 00:01:26
These rockets are the results of Goddard's and other pioneers' imagination and hard work. 00:01:31
Now it's your turn. 00:01:37
You are the next generation of space explorers. 00:01:39
Whoa, that's way cool. 00:01:42
I know, it really is, Zach. 00:01:43
And you know, just as the early space programs of NASA like Mercury, Gemini, and Apollo led 00:01:45
us to the shuttle, the shuttle leads us to the next generation of spacecraft. 00:01:50
What's that? 00:01:55
That's what this show is all about, Seema. 00:01:56
All right, okay, I'm pumped, but how do we get these heavy rockets off the ground? 00:01:58
You know, Zach, that's a really good question, and what do we mean by the word heavy? 00:02:02
Well, what we call heavy is just a way of measuring gravity. 00:02:06
Gravity is a force of attraction between objects. 00:02:10
Everything in the universe is attracted to everything else. 00:02:13
Sometimes it's powerful, but sometimes it's weak. 00:02:17
The amount of attraction really depends on the mass of the objects. 00:02:19
Mass? 00:02:23
James, what do you want me to say? 00:02:24
Hey, Zach, pick Cassie and I up one, too. 00:02:27
Mass is not the same as weight. 00:02:30
Think about how astronauts become nearly weightless in space. 00:02:32
When they are on the moon, they weigh only one-sixth of their weight on Earth. 00:02:36
For example, a man who weighs 180 pounds on Earth would weigh 30 pounds on the moon. 00:02:40
They didn't shrink, did they? 00:02:46
Their mass is the same, so what causes their weight to change? 00:02:48
Gravity. 00:02:51
The force of attraction between objects. 00:02:52
On Earth, we feel gravity because of Earth's mass. 00:02:55
Weight is just how we measure gravity's pull on things. 00:02:59
In space, gravity is less because we are further away from the Earth's mass. 00:03:02
The further away from a large mass like our Earth, the less gravity, and therefore, the 00:03:07
less weight. 00:03:12
What does this have to do with building a spacecraft? 00:03:13
Everything, Zach. 00:03:16
The mass of a spacecraft determines its weight, and the more a spacecraft weighs, the more 00:03:17
force is needed to reach orbit. 00:03:21
Force? 00:03:23
I thought we were talking about gravity. 00:03:24
Hmm, okay, I think we need to talk about some basics here. 00:03:26
Lucky for us, 17th century English scientist Sir Isaac Newton explained the relationship 00:03:29
of mass to gravity. 00:03:35
He said we need force to overcome gravity. 00:03:36
Newton described this relationship as a series of laws. 00:03:41
Newton helped our understanding of gravity with his first law. 00:03:44
What Newton said is easy to understand. 00:03:47
An object at rest will stay at rest unless a force moves it. 00:03:50
With a spacecraft, we need to come up with the force to move it. 00:03:54
So we need to keep the weight, I mean, mass, low, right? 00:03:58
Correct. 00:04:01
Keeping the mass low will mean less weight at launch. 00:04:02
The force of gravity on the spacecraft is equal to the force of the launch pad holding 00:04:05
it up, what Newton called balanced forces. 00:04:09
We have to unbalance these forces to move the spacecraft. 00:04:13
How do we do that? 00:04:17
Well, Cassie, Newton explained in his second law that if a force is applied to a body of 00:04:18
mass, the body will move in the direction of the force. 00:04:22
Newton also described in his third law that for every action, there is an equal and opposite 00:04:26
reaction. 00:04:30
The thrust of a rocket motor is the action. 00:04:32
The reaction is the spacecraft leaving the pad. 00:04:35
Thrust measures the power of a rocket engine. 00:04:38
The thrust must be greater than the force of gravity that keeps a rocket on the launch 00:04:41
pad. 00:04:45
For example, if the thrust, T, of a rocket is 75 kilograms and the weight of the rocket, 00:04:46
W, is 50 kilograms, then subtracting 50 from 75 would equal 25 kilograms of upward force, 00:04:53
To get into orbit, you need to keep the upward force greater than the force of gravity. 00:05:03
When you ride an amusement park ride like the Space Shot here at the Space and Rocket 00:05:07
Center, you are overcoming gravity as you rise up. 00:05:14
At the top, you experience free fall or microgravity, just like the astronauts. 00:05:18
You just don't stay in free fall very long because you drop back downward as the downward 00:05:24
force of gravity becomes greater than the upward force. 00:05:29
That was awesome! 00:05:32
The force of gravity is measured in units called Gs. 00:05:34
At sea level, that force equals 1G. 00:05:39
So we need more than 1G of force to move the rocket? 00:05:42
Pretty much, Seema, but, you know, it's not as easy as it sounds. 00:05:46
Let's take the Saturn V rocket of the Apollo program. 00:05:49
Now, how much do you think that rocket weighed at launch? 00:05:51
Remember how fast a spacecraft needs to travel in order to reach orbit. 00:05:55
Yes, 17,500 miles per hour. 00:05:59
Correct! 00:06:02
And that's over 28,000 kilometers per hour. 00:06:03
The Saturn V is taller than the Statue of Liberty and weighed over 6 million pounds 00:06:06
at launch. 00:06:11
The Saturn V's engines had to produce over 7.5 million pounds of thrust to have enough 00:06:12
upward force to overcome the downward force of gravity. 00:06:18
Okay, I get it. 00:06:22
If we keep the weight of the rocket down, we won't need as much engine thrust to move 00:06:24
it. 00:06:27
Right! 00:06:28
You guys are so smart. 00:06:29
You know, engineers deal with this all the time. 00:06:30
They use math to compare the vehicle weight to the thrust of the engines. 00:06:32
Now, this can be written as a ratio, and a ratio is just a simple way of comparing one 00:06:36
thing to another. 00:06:40
In this case, vehicle weight compared to thrust. 00:06:41
So let's talk about the Saturn V. Let's say it weighs a million pounds and it produces 00:06:45
a million pounds of thrust. 00:06:50
The ratio for that would then be 1 to 1 and wouldn't go anywhere. 00:06:52
But the Saturn V's engines created 7.5 million pounds of thrust and the vehicle weighed 6 00:06:55
million pounds. 00:07:00
Yeah, so that's a ratio of 7.5 to 6, or let's see, 5 to 4. 00:07:01
Exactly. 00:07:08
Now you see how important it is to build rockets more lightweight. 00:07:09
A couple of ways NASA scientists and engineers tackle this problem is by using lightweight 00:07:12
materials and designing more efficient engines. 00:07:18
Today, NASA is working on the next generation of reusable spacecraft, or Launch Vehicle 00:07:21
System. 00:07:26
We call it the Space Launch Initiative, or SLI for short. 00:07:27
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Idioma/s:
en
Materias:
Matemáticas
Niveles educativos:
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Autor/es:
NASA LaRC Office of Education
Subido por:
EducaMadrid
Licencia:
Reconocimiento - No comercial - Sin obra derivada
Visualizaciones:
197
Fecha:
28 de mayo de 2007 - 16:52
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
07′ 32″
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:
45.17 MBytes

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