 So my name is Bruce Schaena. Today I'd like to take a look at poolies and how they make work easier for us. They can change the direction of force and if we put a couple of them together they can actually change the amount of force that we apply. So let's take a closer look. Now students start the investigation by looking at a single pulley. We put a weight on here, I pull it down and the weight goes up. If I put the same size weight on the opposite side, they balance. There's no change in force. It's simply changing the direction that it's applied. Now let's try this on a larger scale. To give my students a better feel for how poolies and pulley systems work, we're going to have them live something a little bit heavier. We have this homemade seat that's going to attach to the pulley in the pulley systems and then students can lift each other and actually feel the difference as we change its mechanical advantage. We start this demonstration by tying a rope to the upstairs railing and simply attaching a pulley's and pulley combinations to that rope and allow the students to lift each other for short distances so they can feel how that force and distance change from one system to another. Now as our final investigation, we decided to see how many students would be needed to lift our principal, Mr. Wright, using a pulley and each of the pulley combinations. We'll start with a single pulley and see what happens. I'm not feeling good about this. Okay, so how many students doesn't take to lift Mr. Wright with this one? Okay, we have six. So what's our mechanical advantage here? One. Okay, so whatever he weighs, that's how much force you guys have to apply. Now let's take a look at a pulley system. I have a fixed pulley up here and a movable pulley here. Once again, when I pull down on this rope, the weight goes up, but I have to pull twice as far to get this to go up half the distance. But the advantage is I don't have to pull as hard. This has a mechanical advantage of two, so I only have to pull half as much as what these weigh. In fact, I can demonstrate that by putting one weight on the rope that I pull down and it balances. Now let's go try this and see if that makes any improvement in a larger system. Here's our setup for the first pulley system. So if you can lift them. How many students are we using this time? We have four. Okay, now if he goes up one, if Mr. Wright's going up one meter, how far do you guys have to pull? Two times as far. Okay, good. Now I jumped off, see if I can make you all pull down. Now let's see if we can make it even easier. In this case, I have a double pulley up here, and a double pulley down here. This is a string I pull down on. It goes up, it comes down, it goes up, it comes down, it goes up, attaches to the fixed pulley. Whatever force I apply here is increased four times here. But I have to pull this out four times further. So let's see how much easier it makes it to lift the principal mass. So here's a setup for this next system. Three, four, four. Count them off. What do we got? Four, four. Four, four. Four, four. Okay. Three girls, let's see if we can do it. No, I don't want to do it. I'm not going to do it. I'm not going to do it. I'm not going to do it. I'm not going to do it. I'm not going to do it. I'm not going to do it. Now let's try this one last time. I have a triple pulley and a triple pulley for mechanical advantage of six. It means whatever force I apply here is increased six times here. It also means I'm going to pull this out six times further. So let's see if we can use this mechanical advantage and get a single student to lift our principal. Okay, Count, see if you can lift it. No, we're good. It's okay, it won't be good. It's too much. Hold on. Wait, wait. Wait, wait. You're right at the point. You're awesome. It was like a scary. That was not a joke. Put off the ground. Okay, let's see if the break works. Let's see. Hey, it doesn't work. All the way up to the rear end of the 5050. You have to have that one the way up. The reason why this pulley system and all pulley systems makes it easier to lift is that you're trading force for distance. In this case, each one of those ropes between the pulleys is lifting up with the same amount of force that's being pulled down on that single strand. So the force has increased six times. Now this also means, however many strands there are, that's how many times further you must pull the rope that you're applying the force to. It's absolutely possible. This right had one last question. Would he be able to lift himself? This method even makes it easier. Since he's pulling on that rope himself, he now has seven ropes that are supporting him. So he only has to apply about one-seventh of his body weight. Let's go. Let's go.