 Hello, welcome to San Francisco Public Library's STEM Challenge Yourself. I am Liberia Joseph. You might remember me from previous challenges as presenter. This week I'm excited to introduce five engineer, physics, and computer programming challenges produced by Yale 2020 interns. For today's challenge, a team of Yale interns produces amazing, fun, engaging, and unique challenge. Are you ready? Teams, take- Episode of STEM Challenge Yourself. My name is Ryan and I will be your host for the day. Today, we will be building a pencil catapult and learning about the science concepts behind it, such as gravity, mass, and energy transfer. Make sure you check out this other video produced by the librarians where they covered force and inertia because we will be building off those concepts. Hi, my name is Colton and the materials you're going to need for this pencil catapult are 12 pencils, some rubber bands, some cardboard, masking tape, and scissors. Let's get started. For this first step, you're going to need three pencils and three rubber bands. Now, put these pencils in a little triangle formation and then overlap the edges a little bit. I'd say just to the end of the metal parts. Then, take these rubber bands and connect the pencils where they intersect or cross over. Now, I'm going to show you how I would connect these. You take the two pencils and one of the rubber bands, put it over the edge of the two pencils, twist it, put it over again, twist it, and then keep doing this until it's nice and tight. Like so. And now, I'm going to do these with the rest and I'll get back to you when I'm done with that. Now that I've built my triangle, you can see that I have two eraser ends pointing down. This is going to give the catapult more stability on its surface. And for our next step, we're going to take three more pencils and three more rubber bands and make the exact same triangle. Alright, the second triangle is built. Now we can move on to our next step. For this step, take one pencil and putting these two side to side, put the pencil on the top part, like so. Like so. Then take two rubber bands and connect the sides. I'll do that right now. As you can see, this catapult isn't very catapult-y. So in this next step, we're going to take two pencils and affix them to the edges here and here. And with rubber bands, of course, I'll get back to you when I'm done. Now for our next step, take a pencil and you can put it right here on one side of either side of the frame. And there's a special way that you can attach this to the frame. You take a rubber band and you put it over the edge, then you go under, then you go over again, under, over, and then loop it over. Like that. I didn't film the time lapse at this part because this is much easier to do with four hands instead of two. My camera person behind the camera helped me with this. Now we're going to set this aside and then take the last two pencils that you have and take some masking tape. Now what you're going to do is you're going to peel off a big old piece of the masking tape, like so, and wrap it around the two pencils. You want to wrap it on both ends and the middle to make it the most stable. This is going to be the thing that holds the launching box that is going to launch, you know, whatever you want to put in there, like coins or something. We've finished this part. Now we're going to put that aside again and take a small, thin piece of cardboard and cut it out to about three inches by three and a half inches. I've already cut it out. I've used a ruler, but you don't have to. So for this step, you're going to take the cardboard and cut little notches into the longer side of the cardboard and then fold those sides into the middle. Then you're going to take these two outer lying sides and fold them up as well and fold the ends in. This is going to eventually make a little tiny cardboard box that you can secure together with tape. All right. Now that we've made our little box, we're going to take this piece with the two pencils and we're going to take this piece that we just made and we're going to take this little box to the end of these pencils here, like so. And now we're going to, this is the launcher. This launcher completely ready. We're going to take this frame that we made earlier and affix this to it. We're going to take a rubber band going carefully over that and under the pencil over again, twist under and then over once more. And there we go. For this next step, we're going to take two rubber bands and tie them in a hitch knot. Now to do this, you put one rubber band through the other and then taking the sides on the inside, pull. All right. Now what I'm going to do with this hitch knot rubber band is I'm going to wrap it around. Oh, it seems like it's not that big. It's not big enough. So I'm going to have to attach another rubber band to it. This is due to the size of my pencils. So don't worry if the two rubber bands don't fit all the way around. You may just need to attach a third. All right. Now that I've added the third rubber band on our little rubber band string, I'm going to thread this rubber band through the frame and then tie it at the end. It's going to be a little bit difficult. You're finished. This is the pencil catapult completed. Now to launch something, say a heavy object like an eraser, you simply put it in the little cardboard box, put your finger down here and all right. But let's try a lighter object like a q-tip. Yeah. Put it in there. Push it down the tiniest bit and wow, that went flying. And now in the spirit of COVID-19, I'm going to launch a little face mask. Now back to you, Ryan. Now that we have built this catapult, let's learn the science behind the reasons why we are able to launch these items with just a simple pull of our fingers. Now, what is energy transfer? Energy transfer is when you use force on something and our energy transfers into the object. The energy we put into it does not disappear because it always goes into something else. We use our energy to push down the pencil and our energy is transferred to the stretching of the rubber band. As the rubber band stretches, there is more tension on it. When we let go, we are transferring the energy from the rubber band into the pencil, which causes the pencil to move and release the coin into the air. What is potential and kinetic energy? Potential energy is stored energy. It is when the object is not moving. In other words, it is the energy that is stored in an object due to its position. For example, potential energy is when the pencil arm is staying still and holding it at the top. Kinetic energy is the energy of an object in motion. In this case, it is when the arm moves to release the object. What is gravity? Gravity is the force that attracts the body toward the center of the earth. The object we launch flies in the shape of an upside-down U due to gravity, which is pointed down. What is mass? Mass is the weight of an object or how heavy an object is. The more the mass, the harder it is to move. If we use a light object, such as a small eraser, to launch on the catapult, it will go further because it does not need a lot of energy or force on it. However, if we use a heavier object, such as a small fruit, and we use the same amount of force to launch it, it will not go as far because it requires more energy to go the same distance. If we want the fruit to move the same distance, we can use more rubber bands to produce more force on the object. Now it's time for you to experiment and explore these concepts yourself. You can explore mass by using coins or a different object to launch and compare the distances they travel. Make sure you are using the same amount of force every time. To explore force, increase the number of rubber bands you are using while launching the same object. Notice how, with more rubber bands or force, the object travels a greater distance. Thank you so much for watching this video. I hope you had a fun time building this catapult and learning with us today. If you want more STEM related experiments, make sure you check out some resources we have provided for you. There are links to the SFPL library's Instagram account and the pom-pom launcher we mentioned earlier. Bye!