Simple machines: Pulleys

Hey guys, this video is the second or third installment of the Rube Goldberg video series 2 that will help you prepare for

simple

machines

in your Rube Goldberg project and this video will be on the pulley, it should be pretty short and nice just for Les I remember some quick things that we were looking at some different concepts where remember that work is constant as long as there is no friction, so the input work is equal to the output work which is done right, so if we write the equation. For work, input force times input distance equals output force times output distance, we can see that if you remember the different variables and what they mean, the box you are moving is the output which is known as load, so it's like the The weight of the box that you're moving, the output distance is how high you end up lifting that box off the ground, so you could say that this little distance here, the force The input is, of course, how hard you have to pull or push. and the input distance is about the distance you pull or push, so we'll look at some

pulleys

here and let's move on to the next slide and I'll add a little image so we can start talking about why our

pulleys

are useful and why they are considered

machines

simple

okay so let's take a picture of a pulley so you can see here this guy pulling he's lifting a barrel so now let's label before we know anything about the police let's label some of the things in this picture and I can use different colors, so this will be the output force and let me make it a little bit thicker so we can see it maybe in blue so you can see it better, so that's my output force, that's the weight of the object you're actually lifting and for us to label the output force, the output distance is like this, it's how high you lifted that barrel off the ground into the pool, so we have to label your input force, which would be how strong is pulling here and the entry distance and it's a little strange to think about this, but it's actually how much rope you've gone through if you started from the beginning of the rope, so we have all those regions and if you think about just do a quick little thing with the inclined plane, it's more or less the same, right, if I lift the box on an inclined plane, the box itself is the force output, the distance the box will move is the input distance just over which my Input force, which is the force with which I am pushing the box, will rise a little bit in height.

Oh, okay, distance so you can see some of the similarities, the barrel is the output force, that's the charge, it's the same as the box. The inclination, the entry distance is the distance over which you apply your force, which would be roughly the length of the rope you pass through the pulley. Now let's take a look at this pulley and see what it's actually used for, so let me. move, actually, okay, just look at it here, how hard does it have to shoot right? Actually, in this image, it actually has to pull exactly the same weight as the barrel, so the pulley here isn't actually reducing its input force because remember. that's what simple machines want to do, they want to reduce the input force by properly increasing the input distance and that will keep the work the same, so basically you have to pull a large amount of rope through the pulley, but you will have to pull with less effort in this image that is not happening, the only thing that pulleys are good for here and this is actually one of the uses of a pulley and there are two uses that you need to know, one of the uses is to simply redirect a force , so instead of him having to stand here somewhere on a little platform and pull up, he can lower it like blinds and you can end up redirecting the force to make it more convenient, but that doesn't make his input force be less so look on the next slide how a pulley can actually make something easier to do here's an example image here we have a fixed pulley which is that and then here we have a moving pulley which is this okay and you can see the one on the left is not actually used for anything except redirection force and that is not considered mechanical advantage by numerical means, so it doesn't actually make the input force less in numerical amount, since I'm Saying the paint bucket has ten pounds you would still be pulling with ten pounds, it's just that you're pulling in a different direction, so it makes it more convenient, but it doesn't make it easier, while the pulley system at the right actually makes it easier, which is pretty cool and you can see that if you really analyze the situation, let me put a different color here and you can see that the ceiling or whatever this wooden thing is is actually holding up half of it. of the weight of the paint, the paint cans, so if that's a 10-pound can of paint, this side holds five pounds, you might remember some of our dynamic problems when we had a painting hanging on the wall and so on. was how it worked now, this would be exactly five pounds because a little bit of an angle, but we're not going to consider that, so I have to pull up on this side and I'm only pulling five pounds even though I'm lifting a 10-pound object. pounds, so that's kind of interesting, so let's take Look at it, it's more complicated, the police use this before, you had to pull up and it may not be as convenient, so let's see if we can redirect it again to do the pull list , so here's a pretty crazy image, just look at each one. consecutively and then we will find out how the pulley is actually useful, so the first one on the left end of this pulley you would have to pull it with a hundred Newtons, all it does is redirect the force, however, the next one the way that What I know is that we will count these two support ropes, now look at the pulley at the bottom, this is movable, so the box is attached to the bottom and it is not attached, the Rebbe, the ropes that go through it and the way I would string it. that pulley is, I would actually start by tying a knot and I'll trace it with me.

I'm going to use this green color. You would start by tying a knot right here. We have wound the rope around this pulley. again around that pulley and I'm going to pull it down like this, if you think about it before the way the last image was on the last slide, you would have had what I'm about to plot in yellow. You had this and you would be pulling up, but we redirected it one more time so we could pull, so here you are going to pull with whatever force is on this outside string, so that would be the one for all of this and this one is 50 Newtons and this one has 15 and you're pulling on that one that still has 50 Newtons, so now you only have to exert 50 Newtons of force, which is great, let's do the next one, here it even does it.

Even better, even more useful, but he agrees again to trace the rope, so now I have a moving pulley on the bottom and I have a double pulley on the top and you can get those where this pulley here is actually mounted correctly. next to that one so it takes up less space, but basically if we're going to trace, we're going to trace from here this is the rope that goes around that, so it's attached, it's fixed, it's attached right there, this one rotates around that pulley, this rope goes through here, we pass it like a yo-yo and then around the top one and I'm pulling it down like this, let's count how many support ropes we have, we have one that will take part of the weight that is going to take some of the weight and that's the way you're pulling right now, it's redirected, so each one of them would be how much do you think if this was about 100 divided by two, which is 50 each? one is one hundred divided by three, which will equal about 33 Newtons each and that is the force you would have to pull with 33 Newtons.

The last rope is the one you are pulling and is redirected downwards in a similar manner. Let's make the following stroke. that one uses this blue one now you see it flips over to hold it here now we have to watch twice the bottom one is mobile, the top ones are fixed on the ceiling, trace the rope that goes around the inside and then goes around the outside and I'm pulling towards down like this, so let's count one, two, three four, so I'm pulling this one outside, one right here, this one outside, that means I'm pulling the, you guessed it, twenty-five Newtons, so if I have more police here more loops of rope I have to make much less effort the last one we could even do it without tracing the rope although you can trace it starts in the middle goes to the second goes to the outside those of us who have one one two three four five six are pulling the one it's way out right here that's redirected so you take a hundred and divide it by six and that's what you're pulling with to make it easier for the stalkers so here's a little trick let's go to the new slide actually , we can do it on this slide.

I'll move the image up a little bit. I'll use them as an example to find the mechanical advantage or I guess I should say the ideal mechanical advantage is that you could calculate the inward distance over the outward distance and get it that way by measuring how much rope you passed over how the skin was raised, but there is An easier way, all you have to do is say that the ima is the number. of loops or support ropes, they are not separate ropes, that's why I say loops, so on this first pulley here it would be one two, that's how much you're pulling now or how many are holding it, so the mechanical advantage is two , so it makes sense and well, we can't take advantage is the number that you would multiply your input force by, okay, and that would mean it was read/write.

I'm pulling with 50 Newtons multiplied by 2, which means I can lift a hundred Newtons. box so that you don't count the rope that you are pulling because it is already counted like this one here, just this one that is wound, so in this one I am going to have one, two, three, so the mechanical advantage would be the support number. loops three very well and let's move on, this would be what you see, it actually counts that it is colored mainly one, two, three, four, make a coveted, simply, it is quite easy in that sense, you can actually combine pulleys with others simple. machines like if you have an inclined plane and you have a pulley on top here you have a box, you have a pulley attached to the box and then you make the little loop pattern, you pull and so you really have to pull with a lot less because the inclined planes They help you and the pulleys help you at the same time, so this is a video about pulleys.

I hope it helps you when you complete your worksheet and good luck creating some designs in the next installment.