![]() When the arm springs forward and launches a ping pong ball the angle it leaves the cup is the launch angle. When the arm of the ping pong catapult is pulled back, the arc distance it travels is called the pull back angle. See the Bibliographyįor more information about the catapult kit. The catapult kit also comes with two different balls (ping-pongĪnd Wiffle®) and enables you to adjust the number of rubber bands. Marks let you measure the pull-back angle (how far back the arm is pulled before launch).Īlso, Figure 3 shows a zoomed-in view of how to measure these angles and Figure 4 labels Which the ball travels relative to horizontal at launch, shown in Figure 1) and tick Has two key features: an adjustable pin lets you set the launch angle (the angle in The catapult kit is pictured in Figure 2, with all of its parts labeled. If you would like to understand where Equations 14 and 15 come from.Īpplying These Principles to the Catapult We have also included a Science Buddies reference page, You can look in the Bibliography or any high-school physics textbook for more information on these topics. This equation is specific to the rubber bands in this catapult kit and will not necessarily be true for every nonlinear spring. Conservation of energy states that, assuming losses like friction in a system are negligible, the sum of kinetic energy (or KE) and potential energy (or PE) always stays the same. Note: We are ignoring a small amount of gravitational potential energy for now.Īll types of energy are usually expressed in units of joules (or J). In our case, we are dealing with kinetic energy (the energy an object with mass has according to its velocity) and potential energy (the energy that is stored in the rubber bands of the catapult). But what about the initial velocity of the ball? We cannot measure that directly, so we will use conservation of energy to estimate what it would be. ![]() It is easy to measure the catapult's height with a tape measure, and the catapult in this kit makes it easy to measure the launch angle (more on that later). 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. You have probably seen figures in your physics textbook that show a catapult launching a projectile and then equations that calculate the resulting trajectory.
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