Hands-on Activity: Right on Target: Catapult Game

Contributed by: Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

A photo shows a young boy aiming his handmade Ping-Pong ball catapult made from wooden sticks, tape, rubber band and a plastic spoon.
An example student-designed and built catapult.
copyright
Copyright © 2009 College of Engineering, University of Colorado Boulder

Summary

Students experience the engineering design process as they design and build accurate and precise catapults using common materials. They use their catapults to participate in a game in which they launch Ping-Pong balls to attempt to hit various targets.
This engineering curriculum meets Next Generation Science Standards (NGSS).

Engineering Connection

The engineering design process is an important aspect of solving engineering challenges, regardless of their nature. This process refers to the steps of designing, building, testing and redesigning a product or system through many iterations in order to achieve solutions that adequately meet the objectives. Whether designing a rocket to take us to the moon, an artificial leg for a runner, or the coolest new toy for kids, engineers follow the steps of the engineering design process.

Pre-Req Knowledge

A familiarty with with catapults, including the math and science behind them, as presented in the associated lesson, Launch into Learning: Catapults!

Learning Objectives

After this activity, students should be able to:

  • Employ the engineering design process to create a solution to a given problem.
  • Design and build catapults using materials found at home.
  • Explain the meaning of projectile motion, accuracy and precision.

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Launch into Learning: Catapults!

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Educational Standards

Each TeachEngineering lesson or activity is correlated to one or more K-12 science, technology, engineering or math (STEM) educational standards.

All 100,000+ K-12 STEM standards covered in TeachEngineering are collected, maintained and packaged by the Achievement Standards Network (ASN), a project of D2L (www.achievementstandards.org).

In the ASN, standards are hierarchically structured: first by source; e.g., by state; within source by type; e.g., science or mathematics; within type by subtype, then by grade, etc.

  • Define a simple design problem reflecting a need or a want that includes specified criteria for success and constraints on materials, time, or cost. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Generate and compare multiple possible solutions to a problem based on how well each is likely to meet the criteria and constraints of the problem. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Plan and carry out fair tests in which variables are controlled and failure points are considered to identify aspects of a model or prototype that can be improved. (Grades 3 - 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • Represent real world and mathematical problems by graphing points in the first quadrant of the coordinate plane, and interpret coordinate values of points in the context of the situation. (Grade 5) Details... View more aligned curriculum... Do you agree with this alignment?
  • New products and systems can be developed to solve problems or to help do things that could not be done without the help of technology. (Grades 6 - 8) Details... View more aligned curriculum... Do you agree with this alignment?
  • Identify and predict how the direction or speed of an object may change due to an outside force (Grade 2) Details... View more aligned curriculum... Do you agree with this alignment?
  • Predict and evaluate the movement of an object by examining the forces applied to it (Grade 8) Details... View more aligned curriculum... Do you agree with this alignment?
Suggest an alignment not listed above

Materials List

Each group needs:

  • 3 sheets of paper (for brainstorming)
  • markers
  • cardboard base (6 x 6 inches)
  • ~48 inches of masking tape
  • plastic spoon
  • 3 rubber bands
  • 8 Popsicle sticks
  • 4 straws
  • 1 Ping-Pong ball

To share with the entire class:

  • targets made of cardboard or foam core board (10 points, 50 points, 100 points and 200 points)

Introduction/Motivation

Today, we are going to use our engineering skills to design catapults for a game! Did you know that many toy companies employ engineers to design toys? We will be working and having fun just like those engineers!

Diagram of words and arrows: Identify problem > brainstorm > design > build-test & evaluate-redesign (cyclical) > share solution.
The steps of the engineering design process.
copyright
Copyright © 2009 College of Engineering, University of Colorado Boulder

Now that we've learned all about catapults from our lesson, we are going to put that knowledge to work. Using some everyday materials, we will create catapults that can launch Ping-Pong balls in a precise and accurate way. We talked about precision and accuracy in the lesson. Let's see what you remember. If your catapult launches Ping-Pong balls so that they all land in the same place but do not hit the target at all, is that an example of accuracy or precision? (Answer: Precision.) If all your Ping-Pong balls hit the target, but in different places on the target, is that an example of accuracy or precision? (Answer: Accuracy.) What if all your Ping-Pong balls hit the target in the same place? (Answer: That demonstrates accuracy and precision!) Now that we've reviewed those terms, we still need to figure out how to design a catapult that is both accurate and precise. Let's start by walking through the process engineers use to go about solving problems like this.

Whenever engineers are faced with a challenge, similar to the one we've just discussed, they use a tool called the engineering design process to help them come up with good solutions. The first step in this process is to identify the problem or challenge. (Write the steps on the classroom board, as each is introduced and explained.) For us, that's easy—we need to develop a machine that can launch Ping-Pong balls in an accurate and precise way. The next step is to brainstorm ideas. You can brainstorm in many ways, but a common method is to draw and discuss ideas as a team. After brainstorming, the best one or two ideas are chosen and formed into an initial design. These designs are drawn on paper, with all individual parts clearly labeled and a list of necessary materials. Once this design is complete, materials are gathered and prototype construction begins. Usually, it is during the construction of this first "prototype" design when unforeseen problems with the design are discovered. Even engineers who have been designing for 20 or 30 years go through this process. So do not expect your catapult to work perfectly the first time! The point is to learn from your mistakes, make changes to the design, and perform lots of tests. After many tests and adjustments, the catapult will eventually work.

The engineering design process involves a loop of building, testing and redesigning many, many times. (Show this with a diagram on the board.) Each new design idea is called a design iteration. For your launching machine, this could be an entirely new design or something as small as a new way to hold the Ping-Pong ball in the spoon. Usually, engineers go through many iterations before they have a design that works well. During this activity, we will design, build and test until we develop machines that complete the challenge objectives!

Vocabulary/Definitions

accuracy: The degree of closeness of a measured or calculated quantity to its actual (true) value. In this activity, accuracy is the ability to hit the target with the Ping-Pong ball.

catapult: A toy/machine that launches a projectile.

precision: The degree to which further measurements or calculations show the same or similar results. In this activity, precision is the ability to hit the same location multiple times with the Ping-Pong ball.

triangle: A polygon with three sides.

Procedure

Before the Activity

  • Set up a table with four targets: 10 points 50 points, 100 points and 200 points. Make simple targets using cardboard or foamcore board. The targets will be used for the game at the end of the activity. Place targets with lower point values closer to the launching area.
  • Gather materials and make copies of the Catapult Design Worksheet, one per student.

With the Students

  1. Review the following information with students:

After completing our launching machines, or catapults, we are going to play a game in which we aim and fire our catapults, trying to hit different targets.Hitting the targets earns you different amounts of points: 10, 50, 100 and 200. We want our catapults to be both accurate and precise in order to hit the maximum number of targets. In addition to making accurate and precise catapults, we also want to make sure that our catapults shoot the Ping-Pong balls far enough to hit the targets. After launching, the balls follow what engineers call "projectile motion." When launching a projectile, a 45º angle causes the object to travel the farthest distance. Keep this fact in mind when you are designing your catapult's launching mechanism.

To propel the Ping-Pong ball long distances, significant forces will be applied to the structure of your catapult in many different directions. Let's review what we learned about force. If the launching part of your catapult is held with a lot of force, your projectile (the Ping-Pong ball) will also be launched with a lot of force. If your Ping-Pong ball is not making it to the target, should you increase the force on the launcher or decrease it? (Answer: Increase.) What if you launch your Ping-Pong ball and it goes way past all the targets? Should you increase or decrease the force on the launcher for the next trial? (Answer: Decrease.)

To make sure that your structure can withstand all of these varying forces, consider using lots of triangles in the frame of your catapult. A triangle is the strongest geometric shape because its sides cannot move unless their lengths change. This means that if you make a triangle using Popsicle sticks, one of the Popsicle sticks would have to break in order for the shape to change. On the flip side, a square or a rectangle can easily compress and change shape into a diamond or other type of quadrilateral without any of the sides changing length. These shifting shapes could lead to a lot of stress on the joints and might cause your catapult to collapse as you try to launch a Ping-Pong ball.

Now that we've covered the science and engineering principles behind catapult design, it's time to apply these concepts and have some fun!

Photo shows three catapults made from wooden sticks, tape, rubber bands and plastic spoons, mounted to cardboard bases.
Figure 1. Example completed catapults
copyright
Copyright © 2009 College of Engineering, University of Colorado Boulder

  1. Divide the class into groups of two or three students each.
  2. Hand out the worksheets.
  3. Direct students to follow the steps detailed on the worksheet. Guide student groups to brainstorm multiple designs and then choose the best design to draw and label. Do not give the students materials until after they have completed their designs and developed a materials list. Give teams who work well together "teamwork tokens," which give the group one extra shot during the game.
  4. Give students time to build their initial catapult designs.
  5. Have groups test their catapult designs, make adjustments and refine their designs(as per the steps of the engineering design process) until it is time to play the game.
  6. Collect all of the catapults at the front of the classroom.
  7. Permit each team to make three shots at each target. Groups with a "teamwork token" may exchange it for one extra shot during the round of their choice.
  8. Add up the points from each round and announce the winning team.

Attachments

Safety Issues

A rubber band mechanism is used to launch Ping-Pong balls, so watch that students are respectful of one another and use the materials without posing danger to others.

Troubleshooting Tips

Students may need to be guided. As they design and build, reinforce the hints that they were given before they began the activity. Remind them that the launching mechanism shoots the ball the farthest if it releases the ball at a 45° angle, triangles are the strongest geometric shape, and that the catapults need to be both accurate and precise.

Investigating Questions

  • Did your catapult work the way you intended?
  • What could you change to make it better?
  • Does your catapult launch the Ping-Pong ball too far past the target or too far to the right or left?
  • What could you do to fix this?

Assessment

Pre-Activity Assessment

Writing Assignment: Assign students to write short paragraphs that answer the following problem question: You are a mechanical engineer who has been challenged to design a machine that can launch a T-shirt 150 feet. What steps would you follow while trying to come up with a solution (do not describe a solution, describe the process you would use to try to come up with a solution)? Have several students read their ideas to the rest of the class. When you discuss the "engineering design process" during the introduction, compare it to the processes developed by each of the students.

Activity Embedded Assessment

Worksheet: Have students complete the Catapult Design Worksheet. Review their answers to gauge their mastery of the subject matter.

Post-Activity Assessment

Class Discussion: As a class, analyze the characteristics of the winning catapult. What made this catapult more accurate and precise than the others? Do you see any simple ways to improve the performance of the catapult?

Activity Extensions

Adjust the mass of the Ping-Pong ball by taping pennies to it. Record how far the catapult launches different masses. Make graphs of this data by placing the number of pennies on the x-axis, and the distance the catapult launched the ball on the y-axis. What does the graph look like?

Activity Scaling

  • For lower grades, give students more direction in designing and building their catapults. For example, develop a design in advance, then guide the students through the basic construction of the frame of that design, so as to limit student design variables to only the launching mechanism.
  • For upper grades, have students measure the angles at which the catapult releases the Ping-Pong balls and the distances the balls travel during the testing. Adjust the catapult at least twice, each time measuring the angles of release and the distance traveled. In this way, students determine the optimum angle of release to send the Ping-Pong ball the farthest.

Contributors

William Surles; Jake Crosby; Jonathan McNeil; Malinda Schaefer Zarske; Carleigh Samson

Copyright

© 2011 by Regents of the University of Colorado

Supporting Program

Integrated Teaching and Learning Program, College of Engineering, University of Colorado Boulder

Acknowledgements

This digital library content was developed by the Integrated Teaching and Learning Program under National Science Foundation GK-12 grant no. DGE 0338326. However, these contents do not necessarily represent the policies of the National Science Foundation, and you should not assume endorsement by the federal government.

Last modified: July 18, 2017

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