 My name is Bryce, and I'm a Yale 2020 intern at the San Francisco Public Library. Today, I'm going to be making a homemade catapult launcher. I'm going to be using cotton balls, but you can always use any light material that you find in your house. Here are the materials that you'll need. Popsicle sticks, around eight, rubber bands, at least five, glue, plastic bottle cap to hold a cotton ball, such as I used a sprite bottle. Cotton ball, if you do not have any available, you can make a small ball by crumbling some paper. A small open area, one square meter will do. It should be a sturdy flat surface, such as a table or a floor. And optional, some markers if you want to decorate your invention. So let's get started. You can pause any time during the video, so that way you can follow along. First, take six craft sticks out of the eight that you have, stack them one on top of the other, security sticks together by wrapping rubber bands around both ends of the stack. You will anchor the launching stick to this stack as as described in the next step. To add this launching stick, take one stick, and you're going to attach it perpendicular to the stack that you just made around the middle, so that way you kind of make like a cross. You can do this with one or two rubber bands that are crossed in an X over the sticks. As shown, if you cross it this way, the sticks will stay nicely perpendicular. If you make them parallel, they won't stay perpendicular, so make sure to put the rubber bands in an X. Next, you are going to add the base by attaching a stick to one end of the launching stick, the stick that you just attached with the rubber band. If it were not for the stack of sticks in between, the launching stick would fall flat on top of the base. But now this launching stick and the base form of V shape lying on its side with a stack of sticks in the middle. So you can see that basically you're making a V with the launching stick and the stick in the bottom, but you're making it perpendicular with the launching stick as well and the stack of sticks that you wrap with a rubber band. Now you're going to put your catapult on the base and you're going to locate the end of the launching stick that sticks up. And you're going to glue the bottle cap there, so that way it forms a small cup to hold the cotton ball as shown. And then you're going to wait until the glue is dry. Alright, so once the glue has been dried and it looks like the bottle cap is kind of like stuck to the stick, now it's time to launch your catapult. So you want to put your catapult in an open area and then you want to put a cotton ball inside of the launching cup, put it on like a flat surface such as a table, which I'm doing, or you can do it on a hard floor. Then you're just going to push the cup down a little bit and let go. Alright, so once you've done that, now try pushing the launching stick more than you did before. Did it go higher and faster? Did it just go higher or did it just go faster? And now we're going to explain the science behind how the cotton ball can fly in the air. When you bend your stick, you load your launching stick up with energy. When you let go, this energy is released and converted to energy of motion. Most of this energy transfers to the cotton ball, which shoots through the air. Pushing the stick down further takes more effort from you. Maybe you felt you needed to exert more force or work harder to bend the stick farther. Bending farther means more energy gets stored in the stick and when you let go, all this stored energy is converted into energy of motion. So the cotton ball flies through the air at a higher speed. In the case of your catapult, the cotton ball probably flew higher and farther. Now here's like a little experiment for you guys to try. Why don't you guys try moving a stack of six sticks and move it closer to the launching cup and try launching the cotton ball now? What kind of results did you get? So if you guys try that, moving the stack of six sticks closer to the launching cup actually makes this launching stick fly farther. This results in a cotton ball aimed more upward than forward. And then if you push your six sticks the other direction, putting them back to where they were originally creates a greater angle between the launching stick and the base. This helps you aim the cotton ball forward. So yeah, thank you guys for listening to my video. Be sure to check out the rest of the STEM Challenge Yourself videos by the SFPO librarians and Yale interns. Hopefully you made an awesome catapult launcher. And I hope you guys play around with it, especially during this quarantine. Bye!