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The Case of the Powerful Pulleys

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Sci Files video containing the following ten segments. NASA Sci Files segment describing how belaying tools and techniques provide a safe means of vertical ascent. NASA Sci Files segment explaining how pulleys make lifiting easier, and how NASA uses

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Hi, I'm Danny Trejo, and I play Uncle Machete in the blockbuster movies Spy Kids and Spy 00:00:00
Kids 2. 00:00:20
As super spies, the Spy Kids have to use all kinds of exciting gizmos and gadgets to help 00:00:21
save the world. 00:00:26
But the real excitement begins in the classroom, as you learn how those gizmos and gadgets 00:00:27
really work. 00:00:32
So you won't want to miss the next big adventure, as the Treehouse Detectives use science, math 00:00:33
and technology to reveal the secrets of simple machines, in order to help Jacob back in the 00:00:38
treehouse. 00:00:44
You can see it all in this episode of Nassau Sci-Files, The Case of the Powerful Pulleys. 00:00:45
Nassau Sci-Files 00:00:57
Nassau Sci-Files 00:01:28
Don't forget to answer the following questions. 00:01:40
What is energy? 00:01:43
What does it mean to do work? 00:01:46
What are simple machines? 00:01:49
When you see this icon, the answer is near. 00:01:52
Nassau Sci-Files 00:01:57
Check this out. 00:02:10
Jacob, watch out! 00:02:12
Jacob? 00:02:18
Jacob? 00:02:19
You got gaffed! 00:02:21
Nassau Sci-Files 00:02:22
The doctor says I'll have to wear this cast for six to eight weeks. 00:02:26
I'm sure it's tough being around in a cast. 00:02:30
Yeah, I guess you have to take it nice and easy. 00:02:33
Well, getting around is still okay. 00:02:37
I really miss being in the treehouse. 00:02:39
You are not climbing up into the treehouse. 00:02:41
He's right, Jacob. 00:02:44
Climbing into the treehouse would be a bad idea. 00:02:45
I'm not going to climb into the treehouse. 00:02:47
But you guys don't know what it's like being stuck in this cast. 00:02:49
The treehouse is like my second home. 00:02:52
Maybe we can figure out a way to get you back into the treehouse without climbing the ladder. 00:02:54
You might be on to something, Bianca. 00:02:58
Stop joking, you guys. 00:03:00
You're getting my hopes up. 00:03:01
We're not joking. 00:03:03
After all, we are the treehouse detectives. 00:03:04
It might take a little while, but we can solve the problem. 00:03:06
I can't wait to get back into the treehouse. 00:03:08
Don't worry, Jacob. 00:03:10
I'm sure we'll have you back in the treehouse in no time at all. 00:03:11
This problem may be tougher than we thought. 00:03:15
Let's brainstorm. 00:03:17
Maybe we could use a rope to pull Jacob up. 00:03:19
Or maybe a trampoline. 00:03:21
A trampoline? That's silly. 00:03:23
Remember, there's no criticism when you brainstorm. 00:03:25
What about lowering the treehouse? 00:03:27
Or we could carry him up. 00:03:29
How much does Jacob weigh? 00:03:31
Probably about 90 pounds. 00:03:33
Well, that's not too much. 00:03:35
You must try my idea of lifting him with a rope. 00:03:37
Let's give it a try. 00:03:39
Can we do this later this afternoon? 00:03:40
Bianca and I are going to Sandy Bottom Nature Park 00:03:42
with my sister's Girl Scout troop. 00:03:44
Dr. D is doing some physics experiments. 00:03:46
Sure. See you this afternoon. 00:03:48
Bye. 00:03:50
It takes energy to do work. 00:03:53
Energy comes in a variety of forms. 00:03:55
The powder in this funnel has potential energy. 00:03:57
It's changed into heat energy when I blow it through this flame. 00:03:59
If I do work and use my energy to stretch this flame, 00:04:07
the energy is stored as elastic potential energy. 00:04:10
And when I let go, 00:04:13
the energy is changed into energy of motion, 00:04:15
or kinetic energy. 00:04:17
Finally, 00:04:19
Flexiglas did the work to stop the tomato. 00:04:21
It takes a lot of work to lift this 25-kilogram anvil. 00:04:24
I have to overcome the pull of gravity. 00:04:27
The anvil now has a lot of gravitational potential energy. 00:04:29
This poor cantaloupe will be smashed. 00:04:32
When I release it, 00:04:35
This poor cantaloupe will be smashed. 00:04:37
When I release the energy by letting go. 00:04:39
Hi, Dr. D. 00:04:48
That was a great show. 00:04:49
I really liked the experiments. 00:04:51
Thanks. 00:04:53
By the way, are you working on any projects? 00:04:54
Well, Jacob has broken his foot, 00:04:56
so we're trying to figure out a way to get him back into the treehouse. 00:04:58
We think we can lift him with a rope, 00:05:02
if we all work together. 00:05:04
Let's talk a little bit about work. 00:05:05
First you have to have a force, a push or a pull. 00:05:07
The force alone is not enough. 00:05:10
To do work, the force must be applied through a distance. 00:05:12
Here, hold onto this anvil for me. 00:05:15
Sure, but why? 00:05:18
Getting tired yet? 00:05:26
You bet. 00:05:27
Because you haven't moved the anvil, 00:05:28
you haven't done any work. 00:05:30
Doing work and getting tired are not necessarily the same thing. 00:05:32
Can we put this thing down? 00:05:36
Of course. 00:05:38
Now, with the slingshot, 00:05:39
I did work when I pulled on the strap 00:05:41
and moved it back about one meter. 00:05:43
When I let go of the strap, 00:05:45
the slingshot did work on the tomato 00:05:46
when it pushed it forward and sped it up. 00:05:48
I love the slack. 00:05:50
Now, with the 25-kilogram anvil, 00:05:52
I had to supply a force of about 55 pounds, 00:05:54
going against gravity as I picked it up. 00:05:57
The higher I lifted the anvil, 00:05:59
the more work I did 00:06:01
and the more gravitational energy the anvil had. 00:06:02
Then the anvil must have had a lot of energy 00:06:05
because it sure crushed the cantaloupe. 00:06:08
But Jacob is heavier than 55 pounds. 00:06:10
Does that mean it would take more work to lift him? 00:06:12
Yes, that's right. 00:06:14
Since work is equal to force times distance, 00:06:15
increasing either the force or the distance will require more work. 00:06:18
You said it took energy to do work. 00:06:21
So where did the energy come from to lift the anvil? 00:06:23
The energy came from the corn flakes I had for breakfast this morning. 00:06:26
Corn got its energy from the sun. 00:06:29
It's going to take a lot of energy to lift Jacob into the treehouse. 00:06:31
I think it's going to take all our energy to do the job. 00:06:34
Thanks, Dr. D. 00:06:37
You're welcome. 00:06:38
Bye. 00:06:39
Bye-bye. 00:06:40
Wow, exactly 3.5 meters. 00:06:43
It's harder than I thought. 00:06:46
My dad had some rope that we can use to lift Jacob. 00:06:48
Great, let's lower it down. 00:06:51
Maybe we could attach it to the test dummy down below. 00:06:52
KCNN is coming on. 00:06:55
Good morning, everyone. 00:06:56
I'm Ted Toombs. 00:06:58
Our top story, Kids Science News Network is getting a facelift. 00:06:59
The next time you see me, I'll be in the new and improved KSNN studio. 00:07:03
Okay, let's get him out of here. 00:07:07
Hey, stop that. 00:07:09
Cut it out. 00:07:11
Put me down. 00:07:12
I'm with Patio Furniture, the studio construction supervisor. 00:07:14
Patty, what can you tell us about the redesign? 00:07:18
We're taking out all the old stuff and replacing it with new stuff, I am. 00:07:23
We're going totally techno here. 00:07:26
We'll have the digital interactive weather board over there, the remote satellite. 00:07:28
Hey, you're not touching with that new skunk. 00:07:32
Sport super slow motion system over here, and the new. 00:07:34
Careful with that dynamite. 00:07:37
Hyper speed wire service feeds in that form. 00:07:39
Well, things are certainly changing around here. 00:07:42
Be sure to join Patty and the KSNN news crew to learn more about our jobs 00:07:46
and why we love them at the upcoming Career Day. 00:07:51
Until next time, I'm I Am Listening for KSNN. 00:07:55
The new studio should be awesome. 00:07:59
You bet. 00:08:01
Is anyone going to Career Day? 00:08:02
Actually, I'm working on a presentation for Career Day. 00:08:03
Aren't you a little young to be thinking about a career? 00:08:06
You're never too young to do research. 00:08:08
That's true. 00:08:10
My mom works for SWE. 00:08:11
I've always been interested in engineering. 00:08:12
What's SWE? 00:08:14
SWE stands for the Society of Women Engineers. 00:08:15
I don't know what I want to be when I grow up, but it's important to know what's out there. 00:08:18
You're right. Maybe we can help you with your presentation. 00:08:22
Don't forget, we have an engineering problem of our own. 00:08:25
That's true. 00:08:28
I've been thinking about our hypothesis. 00:08:29
We could use a rope to pull Jacob back into the tree house. 00:08:31
Well, I better go attach rope to our test dummy. 00:08:33
We were wondering what all the sandbags were doing at the bottom of the tree. 00:08:36
They look heavy. Are you sure you can lift them? 00:08:40
It weighs about 90 pounds, which is almost 41 kilograms. 00:08:42
If we can lift it, Jacob should be no problem. 00:08:45
Okay. We're all set down below. 00:08:47
Well, let's get started. 00:08:49
Are you ready to pull? 00:08:50
Yep. On the count of three. 00:08:52
One, two, three. 00:08:53
Can you two give us a hand? 00:08:58
Thanks. 00:09:01
Wow. It's still hard to pull. 00:09:04
Are you sure this is only 41 kilograms? 00:09:07
This isn't working. 00:09:09
Okay. Let's lower him down. 00:09:12
That didn't work like I thought it would. 00:09:17
We need a new hypothesis. 00:09:19
You're right. We didn't think through the problem very carefully. 00:09:21
I guess we jumped to conclusions too quickly. 00:09:24
We can do this. We just need to get organized and get back to the basics. 00:09:26
The problem board. 00:09:30
Okay. What do we know? 00:09:32
We know we need to get Jacob into the tree house. 00:09:34
And that it's too hard to pull him up with a rope. 00:09:38
Dr. D told us that work requires force applied over a distance. 00:09:41
And that takes energy. 00:09:45
So, what do we need to know? 00:09:47
We need to know an easier way to get Jacob up into the tree house. 00:09:49
Right. There must be a machine that could help. 00:09:52
Like an elevator or a crane. 00:09:54
An elevator sounds great. 00:09:56
I'm not sure what the power source is, but they are made to lift people. 00:09:58
Maybe we could build a small elevator in the tree house. 00:10:01
If we found a way to power the elevator, we could easily lift Jacob. 00:10:04
I think we need to learn more about elevators. 00:10:07
I'll check the internet. 00:10:09
I'll see if I have something in my book bag. 00:10:11
Yes. And check it out. 00:10:17
Elisha Graves Otis invented the elevator in 1853. 00:10:19
After developing a safety device for a lift platform. 00:10:22
I didn't know elevators were that old. 00:10:25
Guys, Otis Elevator has a website. 00:10:27
I wonder if it's the same Otis. 00:10:30
I bet it is. 00:10:32
It says here that they design and install elevators all around the world. 00:10:33
I'll email them and see if they can help. 00:10:37
While you're on the internet, print out an extra get up and go sheet. 00:10:39
You can go to the NASA Sci-Files website to do research and print out your own get up and go sheet. 00:10:42
Hello. We're the tree house detectives and we need to learn more about elevators. 00:10:58
Well, you've come to the right place. 00:11:02
I'm Edith DeFrancesco, Vice President of Product Development here at Otis Elevator Company. 00:11:04
Wow. That sounds interesting. 00:11:08
Do you actually build elevators? 00:11:10
Here at the test tower, we test elevators for safety and efficiency. 00:11:12
And I don't personally build elevators. 00:11:15
Although as a mechanical engineer, I've worked on elevator designs. 00:11:17
You're an engineer? I'm doing a report on engineers for career day. 00:11:20
Great. I'll show you where we design and test our elevators. 00:11:24
We have lots of engineers working on elevator design. 00:11:26
This is our test tower. 00:11:33
After we design the elevators, we bring them here to test them to see how they will work when they're installed. 00:11:35
How do elevators work? 00:11:39
Elevators are driven by electric motors. 00:11:41
And on the motor shaft is a pulley called a shiv. 00:11:43
Over the shiv hang steel cables. 00:11:46
It's basically a box on a rope. 00:11:49
On one end of the cable is the elevator car which carries the people. 00:11:51
And on the other end is the counterweight. 00:11:55
What's a counterweight? 00:11:57
A counterweight is a steel frame full of weights. 00:11:58
And it balances the weight of the elevator car and the people in it. 00:12:01
So that it takes less force to move the elevator. 00:12:04
How does it reduce the amount of force needed? 00:12:07
Think of it like a balance scale. 00:12:09
The force needed to turn the shiv is related to the difference between the weight of the car with the people in it and the weight of the counterweight. 00:12:11
The closer those two are in weight, the more balanced the system is and the easier it is to turn the shiv. 00:12:17
How does an elevator go up and down? 00:12:23
Well, when the motor turns, the shiv rotates. 00:12:26
The cables stay on the shiv in these grooves. 00:12:29
And with the friction between the cables and the shiv, the cables move with the shiv when it rotates, making the elevator go up and down. 00:12:31
It sounds like friction is a good thing to have in an elevator. 00:12:37
Yes, we call it traction and it's very important. 00:12:40
We don't need a very big elevator for our treehouse. 00:12:43
Do elevators come in different sizes? 00:12:46
Yes, they can be as small as a dumbwaiter, about a half a meter by a half a meter. 00:12:48
How big can an elevator be? 00:12:52
Some elevators are as big as a truck. 00:12:54
They're used to carry freight containers at seaports. 00:12:56
But a typical commercial elevator is about a meter by two meters and carries 10 or 12 people. 00:12:58
Designing an elevator seems like a lot of work. 00:13:03
It sounds like a lot of fun. 00:13:05
It has its ups and downs. 00:13:07
Thanks, Mrs. DeFrancesco. We've learned a lot about elevators. 00:13:09
You're welcome. And if you have any more questions, just give me a call. 00:13:12
Bye. 00:13:15
Bye. 00:13:16
Bye. 00:13:17
Wow, I never knew elevators were so cool. 00:13:18
If we're going to build an elevator, we'll need an electric motor, a shove, a shaft, a counterweight, and an elevator car. 00:13:21
Boy, building an elevator sounds expensive. 00:13:27
Not to mention complex. There has to be an easier way to get Jacob up into the treehouse. 00:13:30
What about a ramp? 00:13:35
What, like a bike ramp? 00:13:37
Like that one over there. 00:13:39
Oh, hey, I just got an email from Bianca and Anthony. 00:13:45
They said that they spoke to an engineer about elevators. 00:13:48
That would be great for Bianca's career day presentation. 00:13:51
They also said that an elevator would be too expensive for the treehouse. 00:13:54
And we might want to think about a ramp instead. 00:13:59
What kind of ramp? 00:14:01
You know, ramps that make buildings more accessible to wheelchairs. 00:14:02
Investigate use of ramp. 00:14:06
I have a friend who uses a wheelchair. Maybe he can tell us about what it's like to use ramps. 00:14:10
Let's dial him up. 00:14:16
Hi, our friend Jacob just broke his foot. 00:14:17
And he is learning a little bit about what it is like to be disabled. 00:14:20
Oh, that's too bad, but at least his foot will be well soon. 00:14:23
He really wants to come into the treehouse, but it's not wheelchair accessible. 00:14:27
Have you experienced that? 00:14:31
Yes, a lot of places are not built to accommodate people who are in wheelchairs or have other disabilities. 00:14:33
But today, public places are required by law to be accessible to everyone. 00:14:38
I didn't know that there were laws that require buildings to be accessible to everyone. 00:14:43
What can you do to make buildings accessible to people with disabilities? 00:14:48
Well, a lot of buildings use simple machines, such as a ramp, which is an inclined plane. 00:14:52
Some use elevators, but they are a little more complex. 00:14:58
We need to keep it simple. What is a simple machine? 00:15:01
A simple machine is a device that makes work more convenient by changing the speed, direction, or amount of force. 00:15:04
There are six simple machines. 00:15:11
Inclined plane, levers, wheel and axle, wedge, pulley, and a screw. 00:15:13
We were thinking that a ramp might be the answer to our problem, but we didn't know that they were simple machines. 00:15:19
Are there any requirements for ramps? 00:15:25
If you want to build Jacob a ramp to get into the treehouse, the ramp will need to be built at a 12 to 1 ratio. 00:15:27
That really helps. It gives us a lot to think about. 00:15:35
See you later. 00:15:38
I wonder if there are any other simple machines we need to use to solve our problem. 00:15:39
We need to do more research. 00:15:43
So what's up? How much work will it take to get Jacob into the treehouse? 00:15:48
How will engineering help the treehouse detectives? 00:15:53
Is the ramp the solution to the problem? 00:15:56
Find out next time in The Case of the Powerful Pulleys. 00:15:58
Be sure to answer the following questions during the show. 00:16:03
What is the difference between potential and kinetic energy? 00:16:06
How can pulleys help lift the space shuttle? 00:16:11
How does a pulley make lifting objects easier? 00:16:16
When you see this icon, the answer is near. 00:16:20
Wow, 3.5 meters is much higher than I thought. 00:16:24
Yes, this will be some incline plane. 00:16:27
Let's see. If the incline plane is 3.5 meters high, at a 12 to 1 ratio, that would be... 00:16:30
If the incline plane is 3.5 meters high, at a 12 to 1 ratio, that would be... 00:16:38
With the correct slope, the incline plane would be about here, 42 meters. 00:16:55
It would have to be a really big ramp. 00:17:01
I think ramps are definitely out of the question. 00:17:03
Well, there are other types of simple machines, and we need to know what they are and how they work. 00:17:05
Maybe we could do an internet search on simple machines. 00:17:13
We need to talk to more engineers. 00:17:16
My mom talked to some engineers with her speed group. I'm sure they can help. 00:17:18
Great, let's get to work. 00:17:21
Oh, we just got an email from Dr. D. 00:17:25
It says he wants to meet us at the circus later. 00:17:28
I wonder what he wants. 00:17:32
I'm curious, but it's Dr. D. and the circus. You know that'll be fun. 00:17:34
I bet he can help. I'm sure he knows all about simple machines. 00:17:37
I'll go check on Jacob, and let him know how we're doing. 00:17:41
Look, Dr. D. is balancing up on that big ball. I hope he doesn't fall off. 00:17:49
Hi, Dr. D. It looks like you're having a great time. 00:17:53
Hey, I'm right there! 00:17:57
There's a lot of science here at the circus center. 00:18:05
Science? I never knew that there could be science at a circus. 00:18:08
Sure there is. The circus is a great place to get some ideas to help you solve your problem. 00:18:12
We're particularly interested in simple machines. 00:18:17
Great. Right now they're using a teeter board, which is a lever with a fulcrum or rotational point in the middle. 00:18:20
How does it work? 00:18:26
Well, let's watch this. 00:18:28
That was pretty neat. 00:18:35
I noticed that two men jumped on the board, but only one flew into the air. 00:18:37
Those two men that jumped are called pitchers. The one that flew up in the air is called a flyer. 00:18:41
I should have guessed that one. 00:18:46
After the pitchers jump, they have a lot of potential energy. 00:18:48
It looked like the flyer went at least twice as high as the pitchers. 00:18:51
Exactly. Two men have the same energy as one man twice as high. 00:18:55
Exactly. Two men have the same energy as one man twice as high. 00:18:59
The flyer also helps by pushing off the board. 00:19:03
So the lever didn't create any energy. 00:19:06
That's right. 00:19:08
The lever changes the downward motion of the pitchers to the upward motion of the flyers. 00:19:09
Correct. It's not magic. 00:19:13
The teeter board just lets them transfer energy from the pitchers to the flyer. 00:19:15
How would you like to experience the flying trapeze? 00:19:19
That would be so cool. 00:19:23
Now what does the flying trapeze have to do with energy? 00:19:25
When you are way up there on the platform waiting, you have a lot of potential energy. 00:19:29
Then when you grab the trapeze and swing down, you build up kinetic energy. 00:19:33
And when you swing back again, you lose kinetic energy and pick up potential energy. 00:19:37
Very good. So energy isn't being transferred like on the teeter board. 00:19:41
It's just changing from potential energy to kinetic energy and then back again. 00:19:45
That's why it's the acrobats on the aerial hoop. These guys are really something. 00:19:50
Someone will have to do a lot of work to lift the hoop and the acrobat together. 00:19:55
It looks really easy to pull them up. What are they using with the rope? 00:20:01
It looks like they're using pulleys attached to the rope. 00:20:04
I think this just might be the thing we need to pull Jacob up into the treehouse. 00:20:06
This is great. We're making some real progress. Thanks, Dr. D. 00:20:10
You're welcome. Let's see it by trapeze training. 00:20:13
Let's summarize what we know. 00:20:17
We know that work is force times distance and that it takes energy to do work. 00:20:19
We know that levers change a downward motion to an upward motion. 00:20:22
And that energy changes from potential energy to kinetic energy. 00:20:25
And we also know that pulleys lift large objects more easily. 00:20:28
Okay, so what do we need to know? 00:20:31
We need to know more about pulleys. 00:20:33
I'll bet Nassie uses pulleys. 00:20:35
I'll email my mom and see if she's found any engineers that we can talk to. 00:20:36
And don't forget to email Anthony and tell him what we've learned. 00:20:39
And don't forget to email Anthony and tell him what we've learned. 00:20:43
We're making progress. 00:20:46
That's a great idea. 00:20:47
And we gotta go because we don't want to miss our trapeze class. 00:20:48
Hi, guys. How's the project going? 00:21:06
Great so far. Thanks for your email. 00:21:08
Your mom is friends with Mrs. Jones, an aerospace engineer here at NASA Langley Research Center. 00:21:10
RJ's meeting her at the gantry this afternoon to talk about pulleys. 00:21:14
That's great. 00:21:17
He also said not to worry. 00:21:18
He plans on getting plenty of information for your career day presentation. 00:21:20
Speaking of career day, Kirsten N's coming on. 00:21:23
I'm I Am Listening, live from my dressing room. 00:21:27
During the construction, I'll be filing a series of special reports 00:21:30
about how I personally redesign and overhaul my own dressing room. 00:21:33
And I'm thinking, if this is as easy as it looks, I may just change careers. 00:21:37
This isn't funny anymore. Get me down. 00:21:42
Until next time, I'm I Am Listening for KSNN. 00:21:46
I Am's presentation should be interesting. 00:21:50
How's your report coming, Bianca? 00:21:52
So far so good. 00:21:54
I've researched engineering in general, and the engineer at Otis Elevator was very helpful. 00:21:55
In a way, we're engineers for our pulley project. 00:22:00
Right, but we still have a long way to go. 00:22:02
Have you found anything on the Internet about pulleys? 00:22:04
There's lots of information on the NASA website. 00:22:06
It looks like Ms. Enix from Dryden can help us with pulleys. 00:22:08
Let's dial her up. 00:22:11
Hi, I'm Kimberly Enix, an aerospace engineer, 00:22:14
working here at the Propulsion and Performance Branch at NASA Dryden Flight Research Center. 00:22:18
Wow, an aerospace engineer. 00:22:23
What does an aerospace engineer do? 00:22:26
I do flight test research on different types of aircraft. 00:22:28
What do you do? 00:22:31
I do flight test research on different types of planes. 00:22:32
We actually put our experiments on real jet engines, 00:22:35
install the engines in experimental planes, and then we go out and fly them. 00:22:38
That sounds really cool. Add that to the career list. 00:22:42
We're doing a project, and we need to learn more about pulleys. 00:22:46
We saw on the website that NASA uses pulleys to lift the Space Shuttle onto the back of a 747 plane. 00:22:49
How can pulleys help lift the Space Shuttle? 00:22:54
To lift the Space Shuttle, they use the mate-demate device known as the MDD. 00:22:57
The MDD is this large gantry-like steel structure, 00:23:02
where the Space Shuttle receives post-flight servicing 00:23:06
and is prepared for the ferry flight back to NASA Kennedy Space Center. 00:23:10
The MDD has two 100-foot towers that are connected at 80 feet by a horizontal structure. 00:23:14
What does the horizontal structure do? 00:23:21
It controls and guides a large lift beam that attaches to the Space Shuttle to raise or lower it. 00:23:23
There are three large hoists, or pulleys, that are used to raise and lower the lift beam. 00:23:29
Those must be some big pulleys. 00:23:34
Yes, they are. The Shuttle can weigh up to 232,000 pounds, 00:23:37
but each of the three pulleys has a 100,000-pound lift capability. 00:23:42
Operating together, the total lifting capacity of the three pulleys is 300,000 pounds. 00:23:46
But, for safety reasons, we don't exceed 240,000 pounds. 00:23:52
Wow, that's about 120 times. 00:23:57
You're good at math. 00:24:01
There are also two equipment pulleys built into each tower at the 60-foot level. 00:24:03
Each pulley is capable of lifting 10,000 pounds. 00:24:07
Sounds like pulleys can lift a lot of weight and are pretty important at NASA. 00:24:11
What happens to the Space Shuttle once it's lifted? 00:24:15
The Space Shuttle is then placed on special mounts atop the fuselage of the NASA 747 Shuttle Carrier Aircraft. 00:24:18
It is then flown back to the Kennedy Space Center. 00:24:25
The Space Shuttle actually gets a piggyback ride. 00:24:28
About how long does it take? 00:24:31
Depending on the weather, it usually takes one to two days. 00:24:33
Thanks, Ms. Enix. You've been a big help. 00:24:36
You're welcome. Call if you need anything else, and good luck. 00:24:38
Wow, that is so cool. 00:24:42
I can't believe they lift the Shuttle with pulleys. 00:24:44
If the pulleys can lift the Space Shuttle, I'm sure they could lift Jacob. 00:24:47
I took a lot of notes. I'll enter them into the computer so Jacob and the others can check them out. 00:24:50
And with RJ's notes, we should know a lot about pulleys. 00:24:55
Hi, RJ. Bianca's mom said you'd be coming by. How can I help you? 00:25:00
We need to learn more about pulleys. What exactly is a pulley? 00:25:04
Well, a pulley is a simple machine. It's made from a rope and a wheel. 00:25:07
It makes lifting objects easier. 00:25:11
How does it do that? 00:25:13
It changes the direction of the force. 00:25:14
For example, if you're lifting a heavy object off the floor using a pulley mounted to the ceiling, 00:25:16
you can pull down the rope instead of pushing up. 00:25:22
Aren't you using the same amount of force needed to lift an object? 00:25:25
Good question. Yes, you are, but it's easier to pull down than to push up. 00:25:28
So how would I reduce the amount of force needed to lift a heavy object? 00:25:32
If you add a second pulley and you support the load with two ropes, 00:25:36
then you only need half of the force to lift it. 00:25:40
What if you add a third pulley and support the load with three ropes? 00:25:43
If you divide the weight of the object by the number of ropes supporting the load, 00:25:47
then you can determine what kind of force you need to lift the object. 00:25:51
Awesome. So what do you use pulleys for here at NASA Langer Research Center? 00:25:54
As an aerospace engineer and a Level 3 manager of NASA's Aviation Safety Program, 00:25:58
I use pulleys in crashworthiness research. 00:26:03
What's crashworthiness? 00:26:06
Crashworthiness is how well an aircraft protects occupants in a crash. 00:26:08
A team of engineers and I conduct tests and analysis on materials, 00:26:12
on aircraft structures and full-scale aircraft. 00:26:17
Why is that important? 00:26:19
In a real crash, it is very difficult to understand the damage because many things are destroyed. 00:26:21
By conducting controlled crash tests, we can better understand what happens in a real crash, 00:26:25
and then we can develop better designs that will protect the passengers. 00:26:31
You crash real airplanes here? 00:26:35
We sure do, right here at the gantry. 00:26:37
What exactly is the gantry? 00:26:39
The gantry is the Impact Dynamics Research Facility where we perform full-scale crash tests. 00:26:41
It was also used by astronauts during the Apollo missions to practice landing on the moon. 00:26:45
That's cool. How do you crash planes? 00:26:49
A test vehicle is suspended from two swing cables, pulled back and released 00:26:52
to allow the test vehicle to swing into the impact surface below. 00:26:56
The swing cables are pyrotechnically separated from the vehicle just prior to the impact 00:26:59
so that free flight conditions are established. 00:27:03
Airplanes are really heavy. You must need a lot of pulleys. 00:27:06
Actually, we only use one pulley, but it's a pretty big pulley. 00:27:09
How much can you lift? 00:27:12
We currently can only lift up to 30,000 pounds because that's the maximum capacity of the gantry's bridge. 00:27:14
How can you lift 30,000 pounds? 00:27:19
I run steel rope from the lifting device through the pulley and then attach it back to the bridge. 00:27:21
The pulley is attached to the aircraft. This is called double hitching. 00:27:25
30,000 pounds is a lot of weight. 00:27:28
Yes, it is, but we don't need 30,000 pounds of force to lift it. 00:27:30
With one pulley attached to the aircraft, you have two ropes supporting the load. 00:27:33
Then you only need 15,000 pounds of force. 00:27:37
Alfred and Jacob doesn't weigh 30,000 pounds, 00:27:40
so I bet we could use pulleys to lift them with no problem at all. 00:27:43
Thanks, Mrs. Jones. 00:27:46
You're welcome, and good luck. Call if you need anything. 00:27:48
Okay. 00:27:50
So what's up? 00:27:52
How will the treehouse detectives use pulleys to lift Jacob? 00:27:54
Will it be safe? 00:27:57
Is there a better solution? 00:27:59
Stay tuned for the answers in the next exciting chapter of 00:28:01
The Case of the Powerful Pulleys. 00:28:04
Look for the answers to the following questions. 00:28:10
How can we determine how much mass is needed to lift a treehouse detective? 00:28:13
And how much mass is needed to lift a load? 00:28:17
What should the treehouse detectives consider to safely lift Jacob? 00:28:21
What are human factors? 00:28:26
When you see this icon, the answer is near. 00:28:31
And because pulleys reduce the amount of force needed. 00:28:36
They're inexpensive, easy to set up, and operate. 00:28:39
You must construct a pulley system. 00:28:42
A pulley system is definitely the way to go. 00:28:45
Okay, so we know we need to use pulleys to lift Jacob up into the treehouse. 00:28:50
But how many do we need? 00:28:54
I checked with the NASA Sci-Files Kids Club from Raleigh, North Carolina. 00:28:56
I'll see if we can talk to them. 00:28:59
Don't forget, we have to design the entire apparatus. 00:29:04
I don't know about an apparatus, but a lift chair and a pulley system should be nice. 00:29:07
Okay, fine. 00:29:11
Seriously, we still need to design and build lift chairs. 00:29:13
And the pulley system. 00:29:16
Right, but we need to test both before we try and lift Jacob. 00:29:18
Guys, the Sci-Files Kids Club. Check it out. 00:29:21
Hi, I'm Katie. I'm Mrs. Nowell's fourth grade class at A.B. Compton Elementary School in Raleigh, North Carolina. 00:29:25
Hi, how may I help you? 00:29:31
Hi, we heard that you were working on an experiment to learn more about pulleys. 00:29:33
That's right. We wanted to find out how pulleys work. 00:29:38
Can you tell us about your experiment? 00:29:41
Sure. First, each group was given 500 gram mass, two double pulleys, a cup, some string, and some pennies. 00:29:43
We hooked the 500 gram mass to the bottom of the pulley system that we constructed. 00:29:53
Their combined mass is called the load. 00:29:58
What did you do with the pennies? 00:30:00
We kept adding pennies to the cup until the load was lifted. 00:30:02
We then placed our cup on a balance to find the total mass that it took to lift the load. 00:30:06
Once we collected our data from two strings, we repeated with three and four strings. 00:30:11
Did each group in the class get the same data? 00:30:17
Not exactly. So we shared our data and took the class average of the total mass that it took to lift the load for each number of strings. 00:30:20
When you analyzed your data, were you able to come to any conclusions? 00:30:29
Yes. After putting the class averages up on the board, it was pretty obvious that the more strings we used, the less mass we needed to lift the load. 00:30:33
How did you calculate how much mass you needed for each string? 00:30:42
We counted the number of strings that supported the load and divided the combined mass by the string count. 00:30:46
We saw right away that there was a problem when we did our first calculation. 00:30:53
What was the problem? 00:30:57
Our mass being lifted was 545 grams. When we had only one string, it should have taken 545 grams to lift it. 00:30:59
Instead, it took an average of 571 grams. 00:31:08
We also found the same thing in each of our other calculations. 00:31:12
Could you have collected your data incorrectly? 00:31:16
That's what we thought at first, or that we had made an error in our arithmetic. 00:31:18
Our teacher gave us a hint. We realized that there was friction in our pulley system. 00:31:23
Friction slows things down and makes it more difficult to lift. 00:31:28
That's why you needed more mass to lift the load. 00:31:33
Right. We concluded that you can find approximately how much mass is needed to lift the load by dividing by the number of strings, but you definitely have to consider friction. 00:31:36
Thanks so much for your help. We won't forget about friction. 00:31:47
You're welcome, and good luck on your project. 00:31:50
I really like that experiment, but another way of looking at it is to say that the pulley multiplies in force. 00:31:54
What? 00:31:59
Look at it this way. If we have a load supported by four strings, the pulleys will allow us to lift something four times heavier than the force we apply. 00:32:00
Oh, I get it. If I apply 10 pounds of force, then I can lift 40 pounds. 00:32:07
Exactly. 00:32:13
Mr. Jones said that we divide the total weight by the number of ropes supporting the load. The kids' club showed us how to do that, too. 00:32:14
So if the total weight is 120 pounds, or 54 kilograms, and we had six ropes supporting the load, then that's about 20 pounds of pulling force, and with friction, maybe a little more. 00:32:21
That would take about six pulleys. 00:32:34
Wow. With my 20 pounds of force, I can lift 120 pounds. I've multiplied my force by six times. 00:32:40
That's our new hypothesis. If we use rope, pulleys, and a lift chair, we can lift Jacob back into the treehouse. 00:32:47
But what if I wanted to lift Jacob by myself? 20 pounds still seems like a lot to me. 00:32:54
Maybe we can multiply our force even more by adding more rope and pulleys. It looks like we have some work to do. 00:33:00
Okay, we're about ready to test. 00:33:18
Wait, wait. We have a three-pulley system. 00:33:20
I wish we'd found six pulleys. Do you think our hypothesis will still work? 00:33:23
It should. With three pulleys, we'll need more force, but I think we can do it. 00:33:27
And the test weight is 120 pounds. 00:33:32
Okay, RJ, I think we're ready. 00:33:35
Ready up here. 00:33:37
Okay, we're ready to go. 00:33:39
Ready up here. 00:33:41
Okay, we're ready to go. 00:33:43
According to my calculations, 120 pounds divided by three supporting ropes equals about 40 pounds of pulling force. 00:33:45
Don't forget friction. 00:33:52
Okay, 45. But we definitely need to pull together. 00:33:54
Okay, everybody ready? One, two, three, pull. 00:33:57
Where's Jacob? 00:34:12
Oops. 00:34:16
Treehouse, we have a problem. We need to do more research. 00:34:18
We need to go to the problem board. 00:34:22
Yeah. 00:34:24
All right, we know that work is a force applied over a distance and that it takes energy to do work. 00:34:27
We also know that a lever can change the direction of a force. 00:34:32
And potential and kinetic energy can change back and forth. 00:34:35
And pulleys reduce the amount of force needed to lift an object. 00:34:38
First, we need to know how to make the lift chair safer. 00:34:41
And we also need to know if there's anything else we can do to use less rope. 00:34:44
Since we don't have any more pulleys, 00:34:48
I think we need to find out if there's another simple machine that we can use to make it easier to lift Jacob. 00:34:50
Until the test dummy fell off, it was difficult to pull. 00:34:54
But now that we know how to do it, we can do it. 00:34:57
We need to make it easier to lift Jacob. 00:35:00
Until the test dummy fell off, it was difficult to pull. 00:35:02
We need to talk to someone about safety. 00:35:05
My mom works with some safety engineers at NASA Langley Research Center. 00:35:07
I'll email her. Maybe she can help us. 00:35:10
I'll go see Dr. D. Maybe he can help us figure out how to use less rope. 00:35:14
We've still got some work to do before we let the real Jacob get anywhere near the treehouse. 00:35:18
Great. My mom wrote back. 00:35:22
Ms. Ryan is a safety engineer, and she's going to meet with us this afternoon. 00:35:24
Great. Let's get up and go. 00:35:28
Hi. We're the treehouse detectives. Are you Ms. Ryan? 00:35:31
Yes. How can I help you today? 00:35:34
We're designing a lift chair and a pulley system 00:35:36
to help get our friend with a broken foot up into the treehouse. 00:35:38
And we want to make sure that it is safe to use. 00:35:40
Well, you've come to the right place. 00:35:42
I am a safety engineer here at NASA Langley Research Center. 00:35:44
What does a safety engineer do? 00:35:47
Well, we do lots of things, 00:35:49
like evaluating projects or jobs to identify potential hazards or risks. 00:35:51
We also develop safety plans and guidelines 00:35:55
that help prevent harmful accidents, incidents, or mishaps. 00:35:58
Wow. That sounds like a cool job. And lots of responsibility. 00:36:01
Yes. And we're doing more than developing rules. 00:36:05
We're actually protecting people, property, and the environment. 00:36:07
And we need to protect Jacob. 00:36:10
What are some things that we should consider? 00:36:12
How much will you be lifting? 00:36:14
About 120 pounds. 00:36:16
You'll need to know if there's a load limit on the ropes, pulleys, or anything else 00:36:18
you will be using in the lifting process. 00:36:21
We hadn't thought of that. 00:36:23
How do you figure out the load limit? 00:36:25
Most of the time it's printed on the packaging of a product. 00:36:27
If not, look for the manufacturer and contact them directly. 00:36:29
We will definitely do that. 00:36:33
Is there a safety catch on your pulley system? 00:36:35
No, I don't think so. 00:36:37
A safety catch or a locking mechanism of some kind are very important 00:36:39
in case the people pulling the rope lose their grip. 00:36:42
It would catch and stop the fall of the chair. 00:36:45
We have a lot to check out and to research. 00:36:47
Also, make sure your equipment is in good working order. 00:36:49
You don't want to use worn or broken equipment. 00:36:52
And don't forget that we have to make sure the tree limb is strong enough 00:36:54
to support Jacob, the lift chair, and the pulley system. 00:36:57
Now you're getting it. 00:37:00
And don't forget about testing your equipment before you lift anyone. 00:37:02
We'll be sure to test everything. 00:37:05
You'll also need to consider human factors. 00:37:07
While you're here at the center, you should talk to Dr. Carla Torello. 00:37:09
She's a human factors engineer. 00:37:13
Great. 00:37:15
I'll give her a call and let her know you're coming. 00:37:16
Thanks. 00:37:18
You're welcome, and good luck with your project. 00:37:19
♪ 00:37:23
Oh, hi, Catherine. 00:37:27
Laura Ryan said you'd be stopping by. 00:37:28
Have a seat. 00:37:30
How may I help you? 00:37:33
Our friend Jacob broke his foot, 00:37:34
and we've designed a lift chair to help him to get into the treehouse. 00:37:36
Ms. Ryan gave us some good suggestions on how to make the chair safer, 00:37:39
but she said that we should also consider the science of human factors. 00:37:42
She said that you could help us with human factors. 00:37:46
I sure can. 00:37:49
Human factors is the design of things, spaces, and processes, 00:37:50
so they fit better with people in terms of how people are designed physically 00:37:53
and how we process information. 00:37:57
Why is it important? 00:37:59
Well, when things or processes or areas are designed 00:38:00
without considering human factors, 00:38:03
they may be really difficult to use, and so they may not be used at all. 00:38:05
So where do you start? 00:38:08
Well, we start with standards and guidelines 00:38:09
that are based on scientific principles. 00:38:11
And, for example, they help us understand how the eye works, 00:38:13
which would help us understand what colors to use in our displays. 00:38:16
Oh, I get it. 00:38:19
Then we use what we know is good for human operators, 00:38:20
and we get real operators involved in the process. 00:38:22
This is called user-centered design. 00:38:25
What are you working on now? 00:38:26
Well, here at NASA Langley Research Center, 00:38:28
we design displays and aiding technologies for airplane cockpits. 00:38:30
We do user-centered design of these concepts by involving real pilots 00:38:33
and testing them in aircraft simulators like this one, the IFD. 00:38:37
What is the IFD? 00:38:40
The IFD is integration flight deck. 00:38:41
The IFD is a copy of the flight deck on the NASA Boeing 757. 00:38:44
We learned that in designing, you have to use the iterative process, 00:38:48
where you test, evaluate, and redesign. 00:38:51
Human factors is sort of like that. 00:38:53
Yes, that's right. 00:38:55
The iterative design process is an important part of user-centered design. 00:38:56
You want to involve users all the way through the process, 00:39:00
from concept formation all the way through to testing in a real environment. 00:39:02
What kind of human factors should we consider for our lift chair? 00:39:06
Well, first you need to define your user population. 00:39:09
Will Jacob be the only one using the chair? 00:39:11
Will other friends use it as well? 00:39:13
We hadn't thought of other users. 00:39:15
It would be nice to have for other people who might need to be lifted. 00:39:17
You need to consider your users' requirements, the design goals, too. 00:39:20
So they may be safety, comfort, usability. 00:39:24
Anything else? 00:39:27
You need to consider the anthropometric characteristics of your users. 00:39:28
Anthropometric? What is that? 00:39:31
Anthropometry is the study of measuring people. 00:39:34
There's static measurements, such as arm length and height, 00:39:36
and then there's functional measurements, such as viewing angle and reach. 00:39:39
Wow, we have a lot to consider. 00:39:43
Thanks, Dr. Lattarella. 00:39:45
Oh, you're welcome. Let me know how your chair works out. 00:39:47
Hi, guys. 00:39:52
Hi, Dr. D. 00:39:53
What have you been doing? 00:39:54
Just went for a bike ride to get a little exercise. 00:39:55
How's your project coming? 00:39:57
We're excited about using pulleys to lift Jacob into the treehouse. 00:39:58
But we ended up with a lot of excess rope. 00:40:01
Are we doing something wrong? 00:40:04
I figured you'd have some questions about pulleys. 00:40:06
So I set up a model over here. Let's try it out. 00:40:08
I have 4 kilograms, or about 9 pounds, attached to this pulley system. 00:40:15
Go ahead and pull on the string. 00:40:19
That's really easy. 00:40:25
Why don't you lift the weight, which we call the load 1 meter. 00:40:26
We'll call this the load distance. 00:40:29
Whoa! 00:40:32
Wait a minute, Anthony. Where did all this string come from? 00:40:45
I don't know. What's wrong? 00:40:48
Nothing's wrong. Let me explain. 00:40:51
Simple machines allow you to multiply your force. 00:40:53
In this case, you can lift an object 8 times as heavy as your force. 00:40:56
Right. We learned from the Sci-Files Kids Club that you count the number of strings supporting the load. 00:41:00
I count 8 strings, and that's why we can multiply our force 8 times. 00:41:07
Very good, but there is a trade-off. 00:41:10
What do you mean? 00:41:12
Remember that work is equal to force times distance. 00:41:13
Okay. 00:41:18
With simple machines like pulleys, you can multiply your force, but not the work. 00:41:19
So in this case, you've multiplied your force 8 times. 00:41:24
But how much string did you have to pull in? 00:41:27
We'll call this your distance. 00:41:32
8 meters. That means our distance is 8 times the load distance. 00:41:38
Does it always work that way? 00:41:42
Yes, it does. 00:41:44
If you multiply your force, the trade-off is that your distance will always be greater than the load distance. 00:41:45
Take a lever, for example. 00:41:52
Why don't I stand over here, and have you try to lift me up by pushing over there. 00:41:58
Try it with just one hand. 00:42:04
Okay. 00:42:06
I can't believe I just did that. That was easy. 00:42:17
Well, if your force is 5 times further from the fulcrum, or over here, 00:42:19
That was easy. 00:42:23
Well, if your force is 5 times further from the fulcrum, or rotational point than the load, 00:42:24
you will multiply your force by 5 times. 00:42:29
But your distance, how far you push down, will also be 5 times greater than the load distance, how far I move up. 00:42:32
This is really cool. 00:42:44
So if simple machines don't allow us to do less work, or need less energy, why do we use them? 00:42:47
I guess it's because they make the work easier. 00:42:53
Excellent. 00:42:55
We still need to make our work easier. 00:42:56
Right now we've multiplied our force 3 times by using 3 pulleys, 00:42:58
but that isn't enough to easily lift the load of 120 pounds. 00:43:01
But if we add more pulleys to multiply the force even more, that means that we have to pull in a lot more rope. 00:43:05
Wow. Maybe we need to use a different kind of simple machine. 00:43:10
Well, don't scrap your pulley idea. 00:43:13
You might want to consider combining other simple machines with your pulley system. 00:43:15
You mean like use a lever with our pulley system? 00:43:19
That's a possibility. 00:43:21
Another one is a wheel and axle. 00:43:23
Take my bike, for example. 00:43:25
This could also be called a crank and axle. 00:43:29
This wheel with the chain attached is the axle. 00:43:31
It's attached to this crank with the pedal. 00:43:34
To find out how this machine multiplies the force, 00:43:37
all we have to do is divide the radius of the crank by the radius of the axle. 00:43:39
RJ, would you make the measurements, please? 00:43:44
The crank is 16 centimeters and the axle is 8 centimeters, 00:43:55
so that means the machine multiplies the force by 2. 00:43:59
That's great. 00:44:02
Another possibility you may want to explore is gears. 00:44:05
I'm going to visit my grandparents in San Diego. 00:44:08
We're planning on going to Legoland. 00:44:10
I bet there are a lot of gears in Legoland. 00:44:12
I'll send them an email and see if I can speak with someone about gears. 00:44:14
Great. 00:44:17
Bye, Dr. D. 00:44:18
Thanks. 00:44:19
Bye. 00:44:20
So what's up? 00:44:22
Will the Treehouse Detectives be able to make the lift chair safe? 00:44:23
How will human factors change the design of the lift chair? 00:44:26
What other simple machines can the Treehouse Detectives use to help them lift Jacob? 00:44:29
Find out in the conclusion of The Case of the Powerful Pulleys. 00:44:33
Answer these final questions and help solve The Case of the Powerful Pulleys. 00:44:39
How does a gear work? 00:44:44
How does a belay make the lift chair safer? 00:44:47
How does a winch help solve the problem? 00:44:51
Can you see this icon? The answer is near. 00:44:55
The Case of the Powerful Pulleys 00:45:08
Hello, Mrs. Savelle. 00:45:26
Hi. You must be one of the Treehouse Detectives. 00:45:27
I understand you need to learn about gears. 00:45:30
We sure do. What exactly is a gear? 00:45:32
A gear is one of the oldest simple machines invented. 00:45:35
In fact, it's a wheel and an axle but with teeth. 00:45:39
Teeth? What kind of teeth? 00:45:43
I'll use these Lego gears to show you. 00:45:45
That's cool. 00:45:48
Gears work when the teeth of one gear mesh with the teeth of another. 00:45:49
The first gear is called the driver or the primary gear. 00:45:58
Notice when I turn it, the next gear or the follower gear rotates in the opposite direction but at the same rotational speed. 00:46:02
What happens when you put two gears together that aren't the same size? 00:46:12
Let's see. Notice that the follower gear is two times larger and has twice as many teeth as the driving gear. 00:46:15
Give it a try. 00:46:23
The follower only rotates half as much as the driver. 00:46:28
That's right. It has half the rotational speed of the driver. 00:46:31
Changing rotational speed is one of the reasons we use gears. 00:46:35
Another reason is to multiply the force on the axle of the follower gear. 00:46:39
We definitely need more force but how do you use gears to multiply force? 00:46:46
It's simple. If you double the size of the follower gear, the force on the axle is twice what it used to be. 00:46:50
Is it always that easy? 00:46:57
You can actually calculate the increase in force by simply dividing the number of teeth on the follower with the number of teeth on the driver. 00:46:59
So in this case, the follower has 40 teeth and the driver has 24. 00:47:08
40 divided by 24 is about 1.7. That means that the force is multiplied about two times. 00:47:12
That's right. You're really good with numbers. 00:47:19
What if there are three gears? 00:47:22
Let's try it. 00:47:24
Here we have a driver with 8 teeth, a follower with 24 teeth, and another follower with 40 teeth. 00:47:26
It looks like the driver gear goes around five times for every one time that the largest follower gear goes around. 00:47:38
Good observation. To find the force multiplier, you divide the 40 teeth of the follower by the 8 teeth of the driver. 00:47:43
That would be five. But what about the middle gear? 00:47:52
The middle gear doesn't make a difference except for the fact that it changes the direction of rotation. 00:47:55
Let's verify our results to see if the force is really multiplied by five. 00:48:00
I'll place five bricks on this lever arm and place one brick the same distance out on the lever arm on the driver gear. 00:48:05
It balances, so we were correct. 00:48:14
We've multiplied the force by five, but the follower doesn't move very much at all. 00:48:16
It's just like a pulley system. 00:48:20
Whenever you multiply the force, you have to pull in a lot of rope to move the load a short distance. 00:48:22
Right. Whenever you use simple machines, there's always a tradeoff. 00:48:26
Dr. D. said the same thing. 00:48:30
He also said that you could combine simple machines in order to get a greater multiplication of force. 00:48:32
Check out this bicycle, for example. 00:48:37
The crank works as a lever. 00:48:40
We have a gear system. 00:48:42
In this gear system, the teeth don't mesh together directly. 00:48:44
They are connected by a chain. 00:48:48
A bicycle uses a lot of simple machines. 00:48:51
When you have more than one simple machine working together, like on the bicycle, it's called a compound machine. 00:48:53
Here's another example. 00:49:01
This crane is a combination of a crank or lever attached to a gear connected to pulleys. 00:49:03
This is really cool. I'll bet that this helps us solve our problem. 00:49:13
Thanks a lot, Ms. Salvell. 00:49:17
You're welcome. 00:49:18
I think this is our new hypothesis. 00:49:24
If we use rope, pulleys, gears, and a lift chair, then we'll be able to lift Jacob into the treehouse. 00:49:26
Okay, we can secure Jacob or anyone else in the lift chair by using this rope and harness. 00:49:34
Yes, and the handles make it safer, too. 00:49:39
As long as the lift chair can support the heaviest passenger, then we're in good shape. 00:49:41
Right. Now all we have to figure out is how to make the pulley system easy enough for everyone to use. 00:49:45
Let's go and see if Anthony sent us an email. 00:49:49
Anthony said that he learned a lot at Legoland about gears and combining simple machines together. 00:49:54
He said that he remembers seeing a lot of things in his garage. 00:49:59
He thinks it might be a good idea to use gears with our pulley system. 00:50:02
He wants us to check with his dad about using it. 00:50:05
I wonder what has gears in it. 00:50:07
We'll have to check this out. 00:50:09
Oh, Dr. D wrote us an email. 00:50:11
He said that if we're concerned about safety, we should talk to his climber friends. 00:50:13
Great. While you're on the Internet, print out a get-up-and-go sheet. 00:50:16
You can print out your own get-up-and-go sheet by going to the NASA SciFiles website research track. 00:50:20
Hi. Are you Mr. Harding? 00:50:29
Yes, that's right. You must be one of the treehouse detectives. 00:50:31
Dr. D tells me you need to learn more about safety. 00:50:34
That's right. Dr. D mentioned that you rock climb. 00:50:37
We were wondering how you make it safe. 00:50:40
I can show you that right here, but first we need to outfit you with the climbing harness to tie the rope into you. 00:50:42
You aren't going to pull me up, are you? 00:50:48
No, you're going to have to do the climbing yourself. The rope is just simply there to keep you safe. 00:50:50
How does that work? 00:50:55
It's called belaying. 00:50:56
I tie one end of the rope into your harness, and then it goes through the eye bolt at the top, and then down to me, the belayer. 00:50:57
It passes through this belay device called an ATC or figure eight. 00:51:05
If you slip and begin to fall, I simply pull on the rope like this, and the friction with the ATC stops the rope. 00:51:09
Are you sure this is going to work? 00:51:15
Let me show you. 00:51:17
Climb up a few feet and then let go. 00:51:19
Okay. 00:51:27
Wow. It stopped me right away. 00:51:33
I told you it would. 00:51:35
Another important safety feature is the type of rope we're using. 00:51:36
It's called a dynamic rope because it has stretch to it. 00:51:39
That way you don't stop too suddenly. 00:51:42
You want to try some rappelling? 00:51:47
What's that? 00:51:49
Let me have my son demonstrate. 00:51:50
Okay. 00:51:53
It looks like he used the same device that you used to belay me. 00:52:04
That's right. I have a belay attached to him to keep him safe. 00:52:07
I'll bet we could use the belay principle as a safety device for a lift chair. 00:52:10
Boy, Jacob sure is heavy. 00:52:23
Simple machines sure help. 00:52:26
I'm glad we don't have to live all this way to look. 00:52:28
Hey, here comes Dr. D. 00:52:30
I'll take off the dummy while you can lower the chair. 00:52:33
Okay. 00:52:35
This looks impressive. How did you put it all together? 00:52:52
Well, the obvious answer was pulleys, but that was just the beginning. 00:52:55
We could only find three pulleys, so the best that we could do was multiply the force three times. 00:52:59
Jacob is way too heavy for that. 00:53:03
Hey, I'm not that heavy. 00:53:05
But we learned that we could combine simple machines, like gears, with the pulleys to multiply the force even more. 00:53:08
There was also a safety concern. 00:53:13
We learned how to use the rock climbing technique of belaying to help keep Jacob safe. 00:53:15
And the winch we found not only had gears, but also a wheel and axle to help make the work easier. 00:53:19
It also had a built-in safety device. 00:53:23
I think it's called a ratchet. 00:53:25
Yes, it is. 00:53:27
A ratchet keeps the handle from spinning wildly or turning backwards if you accidentally let go. 00:53:28
We also learned that simple machines don't reduce the energy needed. 00:53:33
They just make work easier. 00:53:36
Instead of using a very big force for the distance of 3.5 meters up into the treehouse, 00:53:38
we can use a very small force on the crank. 00:53:43
That means that we'll have to turn the crank a lot of times. 00:53:45
Right, and we can all use the system by ourselves to lift up any one of us. 00:53:48
Right, we know the force needed is small, but do we ever figure it out exactly? 00:53:52
No. 00:53:56
Dr. D., can you help us with that? 00:53:57
Sure. 00:53:59
How much do the pulleys multiply the force? 00:54:00
The load is supported by three ropes, so the force is multiplied three times. 00:54:02
Good. 00:54:06
How about the gears on your winch? 00:54:07
We learned at Legoland that we need to count the number of teeth on both gears. 00:54:09
The big gear on our winch has 41 teeth, and the little gear has 10 teeth. 00:54:13
So the gears alone multiply our force about four times. 00:54:17
We've learned a lot about simple machines. 00:54:20
There's also a crank on the winch. 00:54:22
It's got a radius about five times longer than the spool. 00:54:24
That multiplies the force five times. 00:54:27
Right, just like the bicycle crank. 00:54:29
The spool also gathers the excess rope. 00:54:31
And because we use gears and a wheel and axle along with our pulleys, 00:54:33
we didn't have to pull in as much rope. 00:54:36
We multiplied the force three times for the pulleys, four times for the gears, 00:54:38
and five times for the wheel and axle. 00:54:41
But how do those go together? 00:54:43
All you have to do is multiply the three numbers together. 00:54:45
That's easy. Let's see. 00:54:48
Three times four is 12, and 12 times five is 60. 00:54:50
So our compound machine multiplies our force 60 times. 00:54:54
Since two times 60 is equal to 120, 00:54:57
that means that we'll only need about two pounds of force to lift 120 pounds. 00:55:00
So is it true that your force will actually be multiplied 60 times? 00:55:05
Isn't that what the math says? 00:55:08
You can always trust math. 00:55:10
Wait a minute. When we were measuring the force on our spring scale, 00:55:12
when we were testing the pulley system, it read five pounds, not two. 00:55:15
I don't get it. 00:55:19
Well, don't forget what you learned from the Sci-Files Kids Club. 00:55:20
Yes, there's always some friction. 00:55:22
Don't forget about the tradeoff. 00:55:24
Right. If our force is multiplied by 60 times, 00:55:26
then the distance will be 60 times more. 00:55:29
Wow, 60 times 3.5 meters up to the treehouse. 00:55:31
That's about 210 meters. 00:55:35
That's a lot of cranking. 00:55:37
Yes, but it's certainly easier than just pulling him in. 00:55:39
And it's safer, too. 00:55:42
Yeah, but it takes a lot longer. 00:55:43
Let's try it out. We have tested it. 00:55:45
We know it'll be easy and safe. Let's do it. 00:55:47
Let's not move too fast. 00:55:50
Remember, I already have one broken foot. 00:55:51
I don't want another. 00:55:54
Don't worry. We'll take good care of you. 00:55:55
Let us know when you're ready. 00:56:10
Okay. I'm ready down here. 00:56:12
Wow, you guys did it. 00:56:39
I can't believe I'm back in the treehouse. 00:56:41
Simple machines are simply amazing. 00:56:43
Good work, everyone. 00:56:45
It worked perfectly, Dr. D. 00:56:55
Thanks for your help. 00:56:57
You're welcome, kids. 00:56:58
You left the excellent work. See ya. 00:57:00
Bye, Dr. D. 00:57:02
Another successful project. 00:57:04
And this time you guys didn't need my help. 00:57:06
I am ToonBot 3000. 00:57:10
Welcome to the news, news, news. 00:57:12
Top Story, Career Day. 00:57:15
We go live to I Am List, List, Listening. 00:57:18
Thanks, uh, ToonBot. 00:57:22
Well, folks, I discovered that I am no expert on renovations or construction. 00:57:25
And I will not be changing careers. 00:57:30
If you want to talk to some real experts and learn about some great career fields, 00:57:33
come down to Career Day tomorrow. 00:57:38
Back to you, ToonBot. 00:57:40
Bang, bang, bang, bang, bang, bang, bang, bang. 00:57:43
Hi, folks. One last little renovation to take care of. 00:57:48
I'm Ted Toon with KSNN. 00:57:53
That's right. You're doing a presentation tomorrow. How's it coming? 00:57:56
Well, thanks to the treehouse detectives, NASA engineers, and SWE, 00:57:59
I think it's going to turn out great. 00:58:03
This pulley system and lift chair makes you a first-class treehouse engineer. 00:58:05
We're all engineers. 00:58:09
You guys are the best. One question, though. 00:58:11
Does this pulley system work as well going down? 00:58:13
Uh-oh. We didn't think about getting you back down. 00:58:16
Dr. D! 00:58:20
Guys? 00:58:27
Guys? 00:58:29
Guys? 00:58:31
Guys? 00:58:33
Guys? 00:58:35
The NASA Science Files is made possible through the generous support of 00:58:46
Busch Gardens, SeaWorld, and NASA Langley Research Center's 00:58:50
Aerospace Vehicle System Technology Office. 00:58:53
Captioning provided by NEC Foundation of America. 00:58:56
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Autor/es:
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Licencia:
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Fecha:
28 de mayo de 2007 - 15:32
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Enlace Relacionado:
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Duración:
59′ 01″
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.
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