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Gears and Compound Machines

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Subido el 28 de mayo de 2007 por EducaMadrid

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NASA Sci Files segment explaining how simple and compound machines affect the effort necessary to perform tasks involving force.

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Hello, Mrs. Savelle. 00:00:00
Hi, you must be one of the treehouse detectives. I understand you need to learn about gears. 00:00:27
We sure do. What exactly is a gear? 00:00:32
A gear is one of the oldest simple machines invented. In fact, it's a wheel and axle, 00:00:35
but with teeth. 00:00:41
Teeth? What kind of teeth? 00:00:43
I'll use these Lego gears to show you. 00:00:45
That's cool. 00:00:48
Gears work when the teeth of one gear mesh with the teeth of another. 00:00:49
The first gear is called the driver or the primary gear. 00:00:58
Notice when I turn it, the next gear or the follower gear 00:01:02
rotates in the opposite direction, but at the same rotational speed. 00:01:07
What happens when you put two gears together that aren't the same size? 00:01:12
Let's see. Notice that the follower gear is two times larger and has twice as many teeth 00:01:15
as the driving gear. Give it a try. 00:01:22
The follower only rotates half as much as the driver. 00:01:28
That's right. It has half the rotational speed of the driver. 00:01:31
Changing rotational speed is one of the reasons we use gears. 00:01:35
Another reason is to multiply the force on the axle of the follower gear. 00:01:39
We definitely need more force, but how do you use gears to multiply force? 00:01:46
It's simple. If you double the size of the follower gear, 00:01:49
the force on the axle is twice what it used to be. 00:01:54
Is it always that easy? 00:01:57
You can actually calculate the increase in force by simply dividing the number of teeth 00:01:59
on the follower with the number of teeth on the driver. 00:02:04
So in this case, the follower has 40 teeth and the driver has 24. 00:02:08
40 divided by 24 is about 1.7. That means that the force is multiplied about two times. 00:02:12
That's right. You're really good with numbers. 00:02:19
What if there are three gears? 00:02:22
Let's try it. 00:02:23
Here we have a driver with 8 teeth, a follower with 24 teeth, and another follower with 40 teeth. 00:02:26
It looks like the driver gear goes around five times for every one time that the largest 00:02:34
follower gear goes around. 00:02:38
Good observation. 00:02:39
To find the force multiplier, you divide the 40 teeth of the follower by the 8 teeth of the driver. 00:02:41
That would be 5. But what about the middle gear? 00:02:48
The middle gear doesn't make a difference, except for the fact that it changes the direction of rotation. 00:02:51
Let's verify our results to see if the force is really multiplied by 5. 00:02:56
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. 00:03:00
It balances, so we were correct. 00:03:09
We've multiplied the force by 5, but the follower doesn't move very much at all. 00:03:12
It's just like a pulley system. 00:03:15
Whenever you multiply the force, you have to pull in a lot of rope to move the load a short distance. 00:03:17
Right. Whenever you use simple machines, there's always a trade-off. 00:03:21
Dr. D said the same thing. 00:03:25
He also said that you could combine simple machines in order to get a greater multiplication of force. 00:03:27
Check out this bicycle, for example. 00:03:32
The crank works as a lever. 00:03:35
We have a gear system. 00:03:37
In this gear system, the teeth don't mesh together directly. 00:03:39
They are connected by a chain. 00:03:42
A bicycle uses a lot of simple machines. 00:03:44
When you have more than one simple machine working together, 00:03:47
like on the bicycle, it's called a compound machine. 00:03:51
Here's another example. 00:03:54
This crane is a combination of a crank or lever attached to a gear connected to pulleys. 00:03:56
This is really cool. 00:04:06
I'll bet that this helps us solve our problem. 00:04:08
Thanks a lot, Ms. Sauvel. 00:04:10
You're welcome. 00:04:12
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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:
721
Fecha:
28 de mayo de 2007 - 15:32
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
04′ 20″
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:
26.12 MBytes

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