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Force and Distance

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Subido el 28 de mayo de 2007 por EducaMadrid

1794 visualizaciones

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

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Hi guys. Hi Dr. D. What have you been doing? Just went for a bike ride to get a 00:00:00
little exercise. How's your project coming? We're excited about using pulleys 00:00:04
to lift Jacob into the treehouse, but we ended up with a lot of excess rope. Are 00:00:08
we doing something wrong? I figured you'd have some questions about pulleys, so I 00:00:12
set up a model over here. Let's try it out. 00:00:17
I have four kilograms or about nine pounds attached to this pulley system. Go 00:00:23
ahead and pull on the string. That's really easy. Why don't you lift the weight, 00:00:28
which we call the load one meter. We'll call this the load distance. 00:00:35
Wait a minute, Anthony. Where did all this string come from? I don't know. What's 00:00:41
wrong? Nothing's wrong. Let me explain. Simple machines allow you to multiply 00:00:58
your force. In this case, you can lift an object eight times as heavy as your 00:01:03
force. Right. We learned from the Cyphos Kids Club that you count the number of 00:01:07
strings supporting the load. I count eight strings, and that's why we can 00:01:11
multiply our force eight times. Very good, but there is a trade-off. What do you 00:01:17
mean? Remember that work is equal to force times distance. Okay. With simple 00:01:21
machines like pulleys, you can multiply your force, but not the work. So in this 00:01:28
case, you've multiplied your force eight times, but how much string did you have 00:01:33
to pull in? We'll call this your distance. 00:01:37
Eight meters. That means our distance is eight times the load distance. Does it 00:01:46
always work that way? Yes, it does. If you multiply your force, the trade-off is that 00:01:51
your distance will always be greater than the load distance. Take a lever, for 00:01:57
example. 00:02:02
Why don't I stand over here, and have you try to lift me up by pushing over there. 00:02:11
Try it with just one hand. Okay. 00:02:17
I can't believe I just did that. That was easy. Well, if your force is five 00:02:22
times further from the fulcrum, or rotational point, than the load, you will 00:02:33
multiply your force by five times. But your distance, how far you push down, will 00:02:38
also be five times greater than the load distance, how far I move up. 00:02:43
This is really cool. So if simple machines don't allow us to do less work, 00:02:51
or need less energy, why do we use them? I guess it's because they make the work 00:02:58
easier. Excellent. We still need to make our work easier. Right now, we've 00:03:03
multiplied our force three times by using three pulleys, but that isn't 00:03:07
enough to easily lift the load of 120 pounds. But if we add more pulleys to 00:03:10
multiply the force even more, that means that we have to pull in a lot more rope. 00:03:15
Wow. Maybe we need to use a different kind of simple machine. Don't scrap your 00:03:18
pulley idea. You might want to consider combining other simple machines with 00:03:22
your pulley system. You mean like use a lever with our pulley system? That's a 00:03:26
possibility. Another one is a wheel and axle. Take my bike, for example. This could 00:03:30
also be called a crank and axle. This wheel with the chain attached is the 00:03:37
axle. It's attached to this crank with the pedal. To find out how this machine 00:03:41
multiplies the force, all we have to do is divide the radius of the crank by the 00:03:46
radius of the axle. R.D., would you make the measurements, please? 00:03:51
The crank is 16 centimeters and the axle is 8 centimeters, so that means the 00:03:56
machine multiplies the force by two. That's great. Another possibility you may 00:04:08
want to explore is gears. I'm going to visit my grandparents in San Diego. We're 00:04:15
planning on going to Legoland. I bet there are a lot of gears in Legoland. 00:04:19
I'll send them an email and see if I can speak with someone about gears. Great. 00:04:22
Bye, Dr. D. Thanks. 00:04:26
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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:
1794
Fecha:
28 de mayo de 2007 - 15:32
Visibilidad:
Público
Enlace Relacionado:
NASAs center for distance learning
Duración:
04′ 29″
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:
27.07 MBytes

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