 Hi everyone, I'm Reuben and I am one of the librarians here at the San Francisco Public Library. For today's STEM challenge, we are making paper airplanes. Now before we get started, do we all know what STEM means? STEM is an acronym which means science, technology, engineering, and math. So what makes paper airplanes a STEM project? Well, it has to do with the principles of flight. So when an airplane is flying a paper airplane, you are observing the interplay of competing forces that keep your airplane in the air and ultimately bring it to the ground. One force is lift. Lift pushes air down so that the airplane rises up. Then there's thrust. So thrust is the force that propels the airplane forward. Then there's drag. So drag is a force that works opposite of thrust and it slows your airplane down. And finally, there's gravity, which is the force that will ultimately bring your paper airplane to the ground. Okay, so now we are going to make an airplane design. Now before you get started, you could, if you wanted to, decorate your paper airplane with some colored pencils. Well, I'm going to clear some space. What we need to make a paper airplane is just one simple blank eight and a half by 11 sheet of paper just like this. Okay, so we're going to start by taking our paper and we are going to fold it right down the middle the long way just like this. Okay, there we go. So now you have a long rectangle and we will open it up. And when you open it up, you will see there's a nice crease right down the center. So from there, you are going to take one corner of your sheet and fold it right to the middle seam. And what that's going to do is it's going to create kind of a triangle as you'll see here. And then you will do the same thing on the other side. So take that corner, bring it to the center, flatten it out so that there's a nice crease. There we go. So now we have what kind of looks like a little house with a point. Let's see. Okay, next you're going to take your next corner just like that and bring it in to the center to your seam again and flatten that out. All right. So now you'll see your triangle looks a little bit longer with a different point. And then do the same thing on the other side. Pull your corner in just like that, the center and flatten it out. Sometimes when you do this, it doesn't come out exactly symmetrically and that's okay. All right. Now you've got this really pointy shape and you're going to take it, you're going to take that pointy shape and you were going to open it just like this against the crease. So you're not folding it in where you creased it but against the crease and fold it flat like that. Okay. So the next thing you are going to take this long side and you were going to line it up against this long side of the paper so that they're lined up increased against each other just like that. And then we're going to flip our paper over and then do the exact same thing. Take that long side, match it up with the long side at the bottom. Now at this point you have another thing you could do if you wanted to. It's not necessary but you could take some tape and tape along the crease to make sure your paper airplane doesn't fall apart. You see how it kind of opens but it's not necessary. You could if you wanted to. I'll put one on just so you can kind of see how that looks. See and now the paper airplane is not opening. And there we go. We've got an airplane that is ready to fly and now that you've built your paper airplane you can take another sheet of paper and you can build another design just like I did here already and you can take your different designs and fly them. And here's part of the challenge is as you fly them compare how they fly differently from each other. Using what you learned about lift and thrust and drag and gravity, which one do you think is going to fly further? You can test that out. Throw them both. See which one goes further. Also knowing what you know about those forces, which one do you think is going to stay in the air the longest? Fly them both and time them. So why does for example this one stay in the air longer than that one? You'll be able to figure that out just by trying different designs. So thanks for joining me today and have some fun flying your airplanes.