 In this session we're going to build some pulley systems to create mechanical advantage to move, or in this case lift this load. So, let's look at some of the components. Up the top we're going to use this rail as our anchor. Down the bottom is our load. We're going to also refer to this load as the output. We've got a rope that's going to weave in between the load and the anchor. Now we call each of these sections a rope apart. And eventually that rope ends up in someone's hand, so we're going to call this the haul. We're also going to refer to this as the input. So if this is the input, that's the output. Now you see we've got two pulleys in our system. We've got what we call a stationary pulley and a traveling pulley. So let's see what this looks like on paper. So we usually draw a box for our load. Some people draw a triangle, it really doesn't matter. We have a rope that comes up, goes through a pulley. That pulley is attached to an anchor. The rope runs back down through our traveling pulley and runs up to our haul. So our load, our anchor, our haul, our stationary pulley, our traveling pulley. Now what we have here is a simple pulley system. In a simple pulley system, all traveling pulleys move at the same speed and in the same direction as the load. Now we want to establish what the mechanical advantages of our simple pulley system. Now mechanical advantage is a ratio of output to input. So if you remember that's our output, that's our input. We want to work out what the ratio is between those two. So if we suspend the load, we'll see that the load is being supported by three parts of rope, either directly or through the traveling pulley. Which means that the hauler is holding one third of the load. In other words, the input is one third of the output. So if we said that another way, the output is three times the input. So in this case we have what we call a three to one simple pulley system. So let's look now at the direction of the haul. If we haul directly into a traveling pulley, we need a haul in the direction of travel straight up. If we haul out to the side, our load is going to go off track and at some stage we're going to lose all of our mechanical advantage. So to get around that, we can run our haul through a change of direction pulley. So when we haul into a change of direction pulley, it gives us more options for the direction of the haul. But the question is, does that change our mechanical advantage? Do we still have a three to one? So if we look at that closely, there's still only three parts of rope that support our load either directly or through the traveling pulley. So we still have a three to one. But the difference is we're hauling through a change of direction. So we call this a three to one CD. Well some people call it a three to one reaved to disadvantage. So let's have a look at this system. First question is it simple? Well, our traveling pulley is moving at the same speed and then the same direction as the load. So it must be simple. What's the mechanical advantage? Well, we have two parts supporting the load. So it must be a two to one simple. So if we add our change of direction pulley, we've still got a simple two to one, but it's a two to one CD. Back to this one, it's still a simple. All traveling pulleys are moving at the same speed and then the same direction as the load. We've got three parts of rope supporting our load, simple three to one. Add our change of direction pulley. Still a simple three to one, but a three to one CD. Next one. All traveling pulleys moving at the same speed and then the same direction as the load. We've got four parts supporting the load, four to one. Add our change of direction pulley. Still a four to one, but now it's a four to one CD. Next one. All traveling pulleys moving at the same speed and then the same direction as the load. Five parts supporting the load, five to one. Add our change of direction pulley. Still five parts supporting the load. Still a five to one, but in this case a five to one CD. So if you look closely at these four systems, the systems with the even mechanical advantage, the rope is terminated at the anchor. The systems with the odd mechanical advantage, the rope is terminated on the load. So we use this as a checker when we've done our mechanical advantage calculation. So in summary, a simple pulley system has all traveling pulleys moving at the same speed and in the same direction as the load. To determine a mechanical advantage on a simple pulley system, we just count the number of parts that support the load either directly or through the traveling pulleys. If the rope that you are hauling terminates on the load, it must give us an odd mechanical advantage. If the rope that you are hauling was terminated on the anchor, it would be an even mechanical advantage. So this information has been useful. Thanks for watching.