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![]() ![]() We are not finished yet, however - using Equations 8 and 10 requires that we know a few things - the height of the catapult above the ground, the angle at which the ball is launched, and its initial velocity. Now we can use Equations 8 and 10 to plot the motion of a projectile in the (x,y) plane. Projectile motion refers to the method used for calculating the trajectory of a projectile (which can be pretty much any physical object - a rock, a ball, etc.) as it moves through the air. Predicting the trajectory of a ball launched from the catapult requires an understanding of two fundamental physics concepts: projectile motion and conservation of energy. Part of the scientific process involves figuring out what those factors are so you can make better predictions next time. There are many real-world factors that can be difficult to account for in predictions. If the results match, you can conclude that your predictions and the assumptions you used to make them were valid under the circumstances of the test. You can also use physics to predict the trajectory of the ball, and then compare this predicted trajectory to the one you measure from video recordings. Well, it is a lot more fun if you actually get to use a catapult instead of just doing the calculations! In this science project, you will use a catapult to launch ping-pong balls and use a video camera to film their trajectory, or path, as they fly through the air. Record how many make it into the bowl out of 5 attempts.You have probably seen figures in your physics textbook that show a catapult launching a projectile and then equations that calculate the resulting trajectory. Then, from a set distance, students will launch their cotton balls. Teams will have 2 test runs to determine launching distance. The bowl will be in a set location (works well on the floor). Station 1 - Accuracy Cotton balls and a bowl make-up this station. Once students have built their catapults, it is time to launch! These three stations can be adapted to your space, but make sure students record results as they go. Encourage students to think outside the box with the supplies provided! Testing Stations ![]() I demonstrated how to make a simple coke and rubber band catapult and pointed out the main features. I kept it simple by making all supplies available, and I did not have any issues. Once you introduce the various supplies, I found it important to give a couple of examples. You can make all materials available to students or incorporate budgeting by adding a price tag to each supply. I decided to have the following available during the project: To determine a materials list, I researched several ways to build a catapult as well as experimented at home. I really like this PBS resource on using the engineering design process for STEM challenges. ![]() Great resources include: TeachEngineering, Science Behind Catapults, and Pumpkin Chunkin Video. I also encourage reviewing the engineering design process and stressing the importance of testing. Discuss what are the basic features of a catapult. The best way to set-up the activity is to show pictures and videos of various catapult designs. Ensure students have a key design difference between the two such as a different base, launcher, or axle. Working in teams, students brainstorm ideas, select the top two designs, and complete three tests to determine the winning design. I have tried several versions of this challenge with my middle school students, and I believe the most successful activity is to have students build two catapults. Each catapult will undergo three different tests to determine accuracy and power.
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